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GeezerVison is showing github.com — [3.7] gh-95778: CVE-2020-10735: Prevent DoS by very large int() by gpshead · Pull Request #96504 · python/cpython

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@gpshead

@gpshead gpshead commented Sep 2, 2022 •
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Integer to and from text conversions via CPython's bignum int type is not safe against denial of service attacks due to malicious input. Very large input strings with hundred thousands of digits can consume several CPU seconds.

This PR comes fresh from a pile of work done in our private PSRT security response team repo.

This backports #96499 aka 511ca94

  • Issue: CVE-2020-10735: Prevent DoS by large int<->str conversions #95778

Signed-off-by: Christian Heimes [Red Hat] [email protected]
Tons-of-polishing-up-by: Gregory P. Smith [Google] [email protected]
Reviews via the private PSRT repo via many others (see the NEWS entry in the PR).

I wrote up a one pager for the release managers.

Additional review is wise on this 3.7 PR as the backport was more complicated due to internal Python config and startup code cleanup in 3.8 and onwards.

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gpshead and others added 13 commits September 1, 2022 17:42
@gpshead
Backport CVE-2020-10735 to 3.7 from 3.8.
ca77774
This is based off of psrt/CVE-2020-10735-3.8backport branch at cd54fc3.
@gpshead
Add What's New entry.
f145128
@tiran @gpshead
Hack: Force CI run
00a5114
@gpshead
revert 1dae140b610a465b4d3e6fb2109ec13da6093e6d CI hack
7eaad20
@gpshead
Backport ctypes test_macholib fix from b29d0a5.
635e292
This is required for the 3.7 tree to pass on modern macOS.
@gpshead
annotate test_bad_password @requires_zlib.
a2956f3
I don't know why, but macOS in 3.7 CI is failing to build the zlib
module these days so it's exposing this test that didn't have the
proper `@requires_zlib` annotation.

Getting it to build with zlib and other things that are now wrongly
"missing" in the 3.7 CI setup would be nice, but probably involves
invasive backporting of parts of
python@b29d0a5
by a macOS domain expert.

Not worth it.
@gpshead
disable MachOTest.test_find unless macOS 11+ support is backported.
95645b6
This test also appears to require changes to
Lib/ctypes/macholib/dyld.py to work in the existing macOS CI config.
I'm just skipping it, backporting that would be a feature.
Not going to happen in 3.7.

There may be a way to configure macOS CI to use an older macOS and
toolchain instead as an alternate option.  Someone else can figure
that out if so.  This branch only lives for another 9 months per
https://peps.python.org/pep-0537/
@gpshead
Move the whatsnew 3.7.14 text per review.
2cc321e
Thanks Ned!
@gpshead
LOL at my typo
bc83515
@gpshead
Make the doctest actually run & fix it.
76c9c2b
@gpshead
remove a line that prevents doctest error reporting.
e7bc47e
the 3.8 branch got rid of this line already.  it blocks seeing the
actual error while testing a doc build!
@gpshead
Fix the docs build.
0ef7ec0
@gpshead
Update the ABI dump with the new private symbols.
ad13c50
@gpshead gpshead assigned gpshead and ned-deily Sep 2, 2022
@bedevere-bot bedevere-bot added the awaiting core review label Sep 2, 2022
gpshead and others added 3 commits September 1, 2022 21:43
@gpshead
Merge branch '3.7' into CVE-2020-10735-3.7backport
2788f3f
@gpshead
Rename the news file to appease the Bedevere bot.
ca92fd2
@gpshead
Merge branch 'CVE-2020-10735-3.7backport' of github.com:gpshead/cpyth…
67905b2
…on into CVE-2020-10735-3.7backport
@gpshead gpshead assigned zooba Sep 2, 2022
@gpshead gpshead added DO-NOT-MERGE release-blocker type-security A security issue and removed type-security A security issue labels Sep 2, 2022
@gpshead
gpshead requested a review from zooba September 2, 2022 05:38
@gpshead gpshead unassigned zooba Sep 2, 2022
@zooba

zooba commented Sep 2, 2022

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Kinda looks like the Windows issue is the Yield macro conflicting with something from the OS:

 ast.c
C:\Program Files (x86)\Windows Kits\10\Include\10.0.22000.0\um\winbase.h(103): warning C4005: 'Yield': macro redefinition [D:\a\cpython\cpython\PCbuild\pythoncore.vcxproj]
  D:\a\cpython\cpython\Include\Python-ast.h(558): note: see previous definition of 'Yield'
..\Python\ast.c(2706): warning C4002: too many actual parameters for macro 'Yield' [D:\a\cpython\cpython\PCbuild\pythoncore.vcxproj]
..\Python\ast.c(2706): warning C4033: 'ast_for_expr' must return a value [D:\a\cpython\cpython\PCbuild\pythoncore.vcxproj]

Then we see further down that python.exe crashes when run:

  python.vcxproj -> D:\a\cpython\cpython\PCbuild\win32\python.exe
  python.vcxproj -> D:\a\cpython\cpython\PCbuild\win32\python.pdb (Full PDB)
D:\a\cpython\cpython\PCbuild\python.vcxproj(90,5): warning MSB3073: The command "setlocal
D:\a\cpython\cpython\PCbuild\python.vcxproj(90,5): warning MSB3073: set PYTHONPATH=D:\a\cpython\cpython\Lib
D:\a\cpython\cpython\PCbuild\python.vcxproj(90,5): warning MSB3073: "D:\a\cpython\cpython\PCbuild\win32\python.exe" "D:\a\cpython\cpython\PC\validate_ucrtbase.py" ucrtbase" exited with code -1073741819.
D:\a\cpython\cpython\PCbuild\python.vcxproj(90,5): warning MSB4181: The "Exec" task returned false but did not log an error.

Not sure why pythoninfo doesn't display the exit code, but that would likely also show -1073741819.

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zooba
zooba reviewed Sep 2, 2022
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Comment thread Python/ast.c Resolved

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gpshead added 2 commits September 2, 2022 16:12
@gpshead
hexadecimal spelling =)
db48ddc
@gpshead
Work around Windows Yield macro vs Python-ast.h
38ec6a9
mdickinson and others added 2 commits September 4, 2022 09:50
@mdickinson @gpshead
pythongh-95778: Correctly pre-check for int-to-str conversion (python…
39837b6
…#96537)

Converting a large enough `int` to a decimal string raises `ValueError` as expected. However, the raise comes _after_ the quadratic-time base-conversion algorithm has run to completion. For effective DOS prevention, we need some kind of check before entering the quadratic-time loop. Oops! =)

The quick fix: essentially we catch _most_ values that exceed the threshold up front. Those that slip through will still be on the small side (read: sufficiently fast), and will get caught by the existing check so that the limit remains exact.

The justification for the current check. The C code check is:
```c
max_str_digits / (3 * PyLong_SHIFT) <= (size_a - 11) / 10
```

In GitHub markdown math-speak, writing $M$ for `max_str_digits`, $L$ for `PyLong_SHIFT` and $s$ for `size_a`, that check is:
$$\left\lfloor\frac{M}{3L}\right\rfloor \le \left\lfloor\frac{s - 11}{10}\right\rfloor$$

From this it follows that
$$\frac{M}{3L} < \frac{s-1}{10}$$
hence that
$$\frac{L(s-1)}{M} > \frac{10}{3} > \log_2(10).$$
So
$$2^{L(s-1)} > 10^M.$$
But our input integer $a$ satisfies $|a| \ge 2^{L(s-1)}$, so $|a|$ is larger than $10^M$. This shows that we don't accidentally capture anything _below_ the intended limit in the check.

<!-- gh-issue-number: pythongh-95778 -->
* Issue: pythongh-95778
<!-- /gh-issue-number -->

Co-authored-by: Gregory P. Smith [Google LLC] <[email protected]>
@gpshead
backport cherry pick fix: lookup max from the right place.
7f911c1
@gpshead gpshead removed the DO-NOT-MERGE label Sep 4, 2022
@ambv ambv added the 🔨 test-with-buildbots Test PR w/ buildbots; report in status section label Sep 5, 2022
@bedevere-bot

bedevere-bot commented Sep 5, 2022

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🤖 New build scheduled with the buildbot fleet by @ambv for commit 7f911c1 🤖

If you want to schedule another build, you need to add the ":hammer: test-with-buildbots" label again.

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@bedevere-bot bedevere-bot removed the 🔨 test-with-buildbots Test PR w/ buildbots; report in status section label Sep 5, 2022
@ambv

ambv commented Sep 5, 2022

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"12 successful checks" is a little thin, no? test-with-buildbots on 3.8 runs 80 checks. Let's run those here, too, as the 3.8 backport's got some legitimate failures.

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@ambv

ambv commented Sep 5, 2022

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In fact, it looks like the latest test-with-buildbots run on this PR from 3 days ago on 38ec6a9 did indeed have the same ASAN and USAN failures.

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@gpshead

gpshead commented Sep 5, 2022

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"as the 3.8 backport's got some legitimate failures."

I don't believe it does. There is no history of success for those ASAN and USAN builds on the 3.8 and 3.7 branches.

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ypankovych
ypankovych approved these changes Sep 5, 2022
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@ambv

ambv commented Sep 5, 2022

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We looked into this. 3.7 and 3.8 are typically not running address and undefined behavior sanitizers on buildbots. The label-driven trigger on PRs is overly broad and runs configurations that aren't used by us for the oldest branches in regular testing. At least 3.8 fails ASAN and UBSAN without GH-96503 applied as well. I'll leave it to @ned-deily to land this to his branch but I'm landing 3.8.

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@ambv

ambv commented Sep 5, 2022

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@ypankovych, don't leave unsolicited approving reviews without comments, those are not actionable for us.

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@ypankovych

ypankovych commented Sep 5, 2022

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@ambv sorry, that was more of a stamp

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@ambv

ambv commented Sep 5, 2022

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I get it, @ypankovych, your intentions were good. But we get many random stamps on open PRs and when they don't even have a comment saying why that person is confident the PR is good, we can't really do anything with that.

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@ned-deily
ned-deily merged commit 15ec1af into python:3.7 Sep 6, 2022
@bedevere-bot bedevere-bot removed the awaiting core review label Sep 6, 2022
@vstinner vstinner mentioned this pull request Sep 15, 2022
00387: CVE-2020-10735: Prevent DoS by very large int() fedora-python/cpython#51
Merged
stratakis pushed a commit to stratakis/cpython that referenced this pull request Mar 11, 2024
@vstinner @stratakis
00387: CVE-2020-10735: Prevent DoS by very large int()
3eea2df
pythongh-95778: CVE-2020-10735: Prevent DoS by very large int() (pythonGH-96504)

Converting between `int` and `str` in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now
raises a `ValueError` if the number of digits in string form is above a
limit to avoid potential denial of service attacks due to the algorithmic
complexity. This is a mitigation for CVE-2020-10735
(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735).

This new limit can be configured or disabled by environment variable, command
line flag, or :mod:`sys` APIs. See the `Integer String Conversion Length
Limitation` documentation.  The default limit is 4300
digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback
from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

Notes on the backport to Python 3.6:

* Use "Python 3.6.15-13" version in the documentation, whereas this
  version will never be released
* Only add _Py_global_config_int_max_str_digits global variable:
  Python 3.6 doesn't have PyConfig API (PEP 597) nor _PyRuntime.
* sys.flags.int_max_str_digits cannot be -1 on Python 3.6: it is
  set to the default limit. Adapt test_int_max_str_digits() for that.
* Declare _PY_LONG_DEFAULT_MAX_STR_DIGITS and
  _PY_LONG_MAX_STR_DIGITS_THRESHOLD macros in longobject.h but only
  if the Py_BUILD_CORE macro is defined.
* Declare _Py_global_config_int_max_str_digits in pydebug.h.

(cherry picked from commit 511ca94)

pythongh-95778: Mention sys.set_int_max_str_digits() in error message (python#96874)

When ValueError is raised if an integer is larger than the limit,
mention sys.set_int_max_str_digits() in the error message.

(cherry picked from commit e841ffc)

pythongh-96848: Fix -X int_max_str_digits option parsing (python#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with
no value (invalid) when the PYTHONINTMAXSTRDIGITS environment
variable is set to a valid limit.

(cherry picked from commit 4135166)
stratakis pushed a commit to stratakis/cpython that referenced this pull request Mar 11, 2024
@vstinner @stratakis
00387: CVE-2020-10735: Prevent DoS by very large int()
b1d1a7c
pythongh-95778: CVE-2020-10735: Prevent DoS by very large int() (pythonGH-96504)

Converting between `int` and `str` in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now
raises a `ValueError` if the number of digits in string form is above a
limit to avoid potential denial of service attacks due to the algorithmic
complexity. This is a mitigation for CVE-2020-10735
(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735).

This new limit can be configured or disabled by environment variable, command
line flag, or :mod:`sys` APIs. See the `Integer String Conversion Length
Limitation` documentation.  The default limit is 4300
digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback
from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

Notes on the backport to Python 3.6:

* Use "Python 3.6.15-13" version in the documentation, whereas this
  version will never be released
* Only add _Py_global_config_int_max_str_digits global variable:
  Python 3.6 doesn't have PyConfig API (PEP 597) nor _PyRuntime.
* sys.flags.int_max_str_digits cannot be -1 on Python 3.6: it is
  set to the default limit. Adapt test_int_max_str_digits() for that.
* Declare _PY_LONG_DEFAULT_MAX_STR_DIGITS and
  _PY_LONG_MAX_STR_DIGITS_THRESHOLD macros in longobject.h but only
  if the Py_BUILD_CORE macro is defined.
* Declare _Py_global_config_int_max_str_digits in pydebug.h.

(cherry picked from commit 511ca94)

pythongh-95778: Mention sys.set_int_max_str_digits() in error message (python#96874)

When ValueError is raised if an integer is larger than the limit,
mention sys.set_int_max_str_digits() in the error message.

(cherry picked from commit e841ffc)

pythongh-96848: Fix -X int_max_str_digits option parsing (python#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with
no value (invalid) when the PYTHONINTMAXSTRDIGITS environment
variable is set to a valid limit.

(cherry picked from commit 4135166)
stratakis pushed a commit to stratakis/cpython that referenced this pull request Mar 20, 2024
@vstinner @stratakis
00387: CVE-2020-10735: Prevent DoS by very large int()
859b6a4
pythongh-95778: CVE-2020-10735: Prevent DoS by very large int() (pythonGH-96504)

Converting between `int` and `str` in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now
raises a `ValueError` if the number of digits in string form is above a
limit to avoid potential denial of service attacks due to the algorithmic
complexity. This is a mitigation for CVE-2020-10735
(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735).

This new limit can be configured or disabled by environment variable, command
line flag, or :mod:`sys` APIs. See the `Integer String Conversion Length
Limitation` documentation.  The default limit is 4300
digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback
from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

Notes on the backport to Python 3.6:

* Use "Python 3.6.15-13" version in the documentation, whereas this
  version will never be released
* Only add _Py_global_config_int_max_str_digits global variable:
  Python 3.6 doesn't have PyConfig API (PEP 597) nor _PyRuntime.
* sys.flags.int_max_str_digits cannot be -1 on Python 3.6: it is
  set to the default limit. Adapt test_int_max_str_digits() for that.
* Declare _PY_LONG_DEFAULT_MAX_STR_DIGITS and
  _PY_LONG_MAX_STR_DIGITS_THRESHOLD macros in longobject.h but only
  if the Py_BUILD_CORE macro is defined.
* Declare _Py_global_config_int_max_str_digits in pydebug.h.

(cherry picked from commit 511ca94)

pythongh-95778: Mention sys.set_int_max_str_digits() in error message (python#96874)

When ValueError is raised if an integer is larger than the limit,
mention sys.set_int_max_str_digits() in the error message.

(cherry picked from commit e841ffc)

pythongh-96848: Fix -X int_max_str_digits option parsing (python#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with
no value (invalid) when the PYTHONINTMAXSTRDIGITS environment
variable is set to a valid limit.

(cherry picked from commit 4135166)
stratakis pushed a commit to stratakis/cpython that referenced this pull request Mar 20, 2024
@vstinner @stratakis
00387: CVE-2020-10735: Prevent DoS by very large int()
cb8add6
pythongh-95778: CVE-2020-10735: Prevent DoS by very large int() (pythonGH-96504)

Converting between `int` and `str` in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now
raises a `ValueError` if the number of digits in string form is above a
limit to avoid potential denial of service attacks due to the algorithmic
complexity. This is a mitigation for CVE-2020-10735
(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735).

This new limit can be configured or disabled by environment variable, command
line flag, or :mod:`sys` APIs. See the `Integer String Conversion Length
Limitation` documentation.  The default limit is 4300
digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback
from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

Notes on the backport to Python 3.6:

* Use "Python 3.6.15-13" version in the documentation, whereas this
  version will never be released
* Only add _Py_global_config_int_max_str_digits global variable:
  Python 3.6 doesn't have PyConfig API (PEP 597) nor _PyRuntime.
* sys.flags.int_max_str_digits cannot be -1 on Python 3.6: it is
  set to the default limit. Adapt test_int_max_str_digits() for that.
* Declare _PY_LONG_DEFAULT_MAX_STR_DIGITS and
  _PY_LONG_MAX_STR_DIGITS_THRESHOLD macros in longobject.h but only
  if the Py_BUILD_CORE macro is defined.
* Declare _Py_global_config_int_max_str_digits in pydebug.h.

(cherry picked from commit 511ca94)

pythongh-95778: Mention sys.set_int_max_str_digits() in error message (python#96874)

When ValueError is raised if an integer is larger than the limit,
mention sys.set_int_max_str_digits() in the error message.

(cherry picked from commit e841ffc)

pythongh-96848: Fix -X int_max_str_digits option parsing (python#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with
no value (invalid) when the PYTHONINTMAXSTRDIGITS environment
variable is set to a valid limit.

(cherry picked from commit 4135166)
stratakis pushed a commit to stratakis/cpython that referenced this pull request Mar 20, 2024
@vstinner @stratakis
00387: CVE-2020-10735: Prevent DoS by very large int()
758fc4a
pythongh-95778: CVE-2020-10735: Prevent DoS by very large int() (pythonGH-96504)

Converting between `int` and `str` in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now
raises a `ValueError` if the number of digits in string form is above a
limit to avoid potential denial of service attacks due to the algorithmic
complexity. This is a mitigation for CVE-2020-10735
(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735).

This new limit can be configured or disabled by environment variable, command
line flag, or :mod:`sys` APIs. See the `Integer String Conversion Length
Limitation` documentation.  The default limit is 4300
digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback
from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

Notes on the backport to Python 3.6:

* Use "Python 3.6.15-13" version in the documentation, whereas this
  version will never be released
* Only add _Py_global_config_int_max_str_digits global variable:
  Python 3.6 doesn't have PyConfig API (PEP 597) nor _PyRuntime.
* sys.flags.int_max_str_digits cannot be -1 on Python 3.6: it is
  set to the default limit. Adapt test_int_max_str_digits() for that.
* Declare _PY_LONG_DEFAULT_MAX_STR_DIGITS and
  _PY_LONG_MAX_STR_DIGITS_THRESHOLD macros in longobject.h but only
  if the Py_BUILD_CORE macro is defined.
* Declare _Py_global_config_int_max_str_digits in pydebug.h.

(cherry picked from commit 511ca94)

pythongh-95778: Mention sys.set_int_max_str_digits() in error message (python#96874)

When ValueError is raised if an integer is larger than the limit,
mention sys.set_int_max_str_digits() in the error message.

(cherry picked from commit e841ffc)

pythongh-96848: Fix -X int_max_str_digits option parsing (python#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with
no value (invalid) when the PYTHONINTMAXSTRDIGITS environment
variable is set to a valid limit.

(cherry picked from commit 4135166)
stratakis pushed a commit to stratakis/cpython that referenced this pull request Mar 20, 2024
@vstinner @stratakis
00387: CVE-2020-10735: Prevent DoS by very large int()
c91ac07
pythongh-95778: CVE-2020-10735: Prevent DoS by very large int() (pythonGH-96504)

Converting between `int` and `str` in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now
raises a `ValueError` if the number of digits in string form is above a
limit to avoid potential denial of service attacks due to the algorithmic
complexity. This is a mitigation for CVE-2020-10735
(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735).

This new limit can be configured or disabled by environment variable, command
line flag, or :mod:`sys` APIs. See the `Integer String Conversion Length
Limitation` documentation.  The default limit is 4300
digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback
from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

Notes on the backport to Python 3.6:

* Use "Python 3.6.15-13" version in the documentation, whereas this
  version will never be released
* Only add _Py_global_config_int_max_str_digits global variable:
  Python 3.6 doesn't have PyConfig API (PEP 597) nor _PyRuntime.
* sys.flags.int_max_str_digits cannot be -1 on Python 3.6: it is
  set to the default limit. Adapt test_int_max_str_digits() for that.
* Declare _PY_LONG_DEFAULT_MAX_STR_DIGITS and
  _PY_LONG_MAX_STR_DIGITS_THRESHOLD macros in longobject.h but only
  if the Py_BUILD_CORE macro is defined.
* Declare _Py_global_config_int_max_str_digits in pydebug.h.

(cherry picked from commit 511ca94)

pythongh-95778: Mention sys.set_int_max_str_digits() in error message (python#96874)

When ValueError is raised if an integer is larger than the limit,
mention sys.set_int_max_str_digits() in the error message.

(cherry picked from commit e841ffc)

pythongh-96848: Fix -X int_max_str_digits option parsing (python#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with
no value (invalid) when the PYTHONINTMAXSTRDIGITS environment
variable is set to a valid limit.

(cherry picked from commit 4135166)
stratakis pushed a commit to stratakis/cpython that referenced this pull request Mar 25, 2024
@vstinner @stratakis
00387: CVE-2020-10735: Prevent DoS by very large int()
761bd73
pythongh-95778: CVE-2020-10735: Prevent DoS by very large int() (pythonGH-96504)

Converting between `int` and `str` in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now
raises a `ValueError` if the number of digits in string form is above a
limit to avoid potential denial of service attacks due to the algorithmic
complexity. This is a mitigation for CVE-2020-10735
(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735).

This new limit can be configured or disabled by environment variable, command
line flag, or :mod:`sys` APIs. See the `Integer String Conversion Length
Limitation` documentation.  The default limit is 4300
digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback
from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

Notes on the backport to Python 3.6:

* Use "Python 3.6.15-13" version in the documentation, whereas this
  version will never be released
* Only add _Py_global_config_int_max_str_digits global variable:
  Python 3.6 doesn't have PyConfig API (PEP 597) nor _PyRuntime.
* sys.flags.int_max_str_digits cannot be -1 on Python 3.6: it is
  set to the default limit. Adapt test_int_max_str_digits() for that.
* Declare _PY_LONG_DEFAULT_MAX_STR_DIGITS and
  _PY_LONG_MAX_STR_DIGITS_THRESHOLD macros in longobject.h but only
  if the Py_BUILD_CORE macro is defined.
* Declare _Py_global_config_int_max_str_digits in pydebug.h.

(cherry picked from commit 511ca94)

pythongh-95778: Mention sys.set_int_max_str_digits() in error message (python#96874)

When ValueError is raised if an integer is larger than the limit,
mention sys.set_int_max_str_digits() in the error message.

(cherry picked from commit e841ffc)

pythongh-96848: Fix -X int_max_str_digits option parsing (python#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with
no value (invalid) when the PYTHONINTMAXSTRDIGITS environment
variable is set to a valid limit.

(cherry picked from commit 4135166)
hroncok pushed a commit to fedora-python/cpython that referenced this pull request Mar 26, 2024
@vstinner @hroncok
00387: CVE-2020-10735: Prevent DoS by very large int()
31235df
pythongh-95778: CVE-2020-10735: Prevent DoS by very large int() (pythonGH-96504)

Converting between `int` and `str` in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now
raises a `ValueError` if the number of digits in string form is above a
limit to avoid potential denial of service attacks due to the algorithmic
complexity. This is a mitigation for CVE-2020-10735
(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735).

This new limit can be configured or disabled by environment variable, command
line flag, or :mod:`sys` APIs. See the `Integer String Conversion Length
Limitation` documentation.  The default limit is 4300
digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback
from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

Notes on the backport to Python 3.6:

* Use "Python 3.6.15-13" version in the documentation, whereas this
  version will never be released
* Only add _Py_global_config_int_max_str_digits global variable:
  Python 3.6 doesn't have PyConfig API (PEP 597) nor _PyRuntime.
* sys.flags.int_max_str_digits cannot be -1 on Python 3.6: it is
  set to the default limit. Adapt test_int_max_str_digits() for that.
* Declare _PY_LONG_DEFAULT_MAX_STR_DIGITS and
  _PY_LONG_MAX_STR_DIGITS_THRESHOLD macros in longobject.h but only
  if the Py_BUILD_CORE macro is defined.
* Declare _Py_global_config_int_max_str_digits in pydebug.h.

(cherry picked from commit 511ca94)

pythongh-95778: Mention sys.set_int_max_str_digits() in error message (python#96874)

When ValueError is raised if an integer is larger than the limit,
mention sys.set_int_max_str_digits() in the error message.

(cherry picked from commit e841ffc)

pythongh-96848: Fix -X int_max_str_digits option parsing (python#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with
no value (invalid) when the PYTHONINTMAXSTRDIGITS environment
variable is set to a valid limit.

(cherry picked from commit 4135166)
mcepl pushed a commit to openSUSE-Python/cpython that referenced this pull request Apr 2, 2024
@vstinner @mcepl
00387: CVE-2020-10735: Prevent DoS by very large int()
b030834
pythongh-95778: CVE-2020-10735: Prevent DoS by very large int() (pythonGH-96504)

Converting between `int` and `str` in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now
raises a `ValueError` if the number of digits in string form is above a
limit to avoid potential denial of service attacks due to the algorithmic
complexity. This is a mitigation for CVE-2020-10735
(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735).

This new limit can be configured or disabled by environment variable, command
line flag, or :mod:`sys` APIs. See the `Integer String Conversion Length
Limitation` documentation.  The default limit is 4300
digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback
from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

Notes on the backport to Python 3.6:

* Use "Python 3.6.15-13" version in the documentation, whereas this
  version will never be released
* Only add _Py_global_config_int_max_str_digits global variable:
  Python 3.6 doesn't have PyConfig API (PEP 597) nor _PyRuntime.
* sys.flags.int_max_str_digits cannot be -1 on Python 3.6: it is
  set to the default limit. Adapt test_int_max_str_digits() for that.
* Declare _PY_LONG_DEFAULT_MAX_STR_DIGITS and
  _PY_LONG_MAX_STR_DIGITS_THRESHOLD macros in longobject.h but only
  if the Py_BUILD_CORE macro is defined.
* Declare _Py_global_config_int_max_str_digits in pydebug.h.

(cherry picked from commit 511ca94)

pythongh-95778: Mention sys.set_int_max_str_digits() in error message (python#96874)

When ValueError is raised if an integer is larger than the limit,
mention sys.set_int_max_str_digits() in the error message.

(cherry picked from commit e841ffc)

pythongh-96848: Fix -X int_max_str_digits option parsing (python#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with
no value (invalid) when the PYTHONINTMAXSTRDIGITS environment
variable is set to a valid limit.

(cherry picked from commit 4135166)
hrnciar pushed a commit to fedora-python/cpython that referenced this pull request Apr 23, 2025
@vstinner @hrnciar
00387: CVE-2020-10735: Prevent DoS by very large int()
3181653
pythongh-95778: CVE-2020-10735: Prevent DoS by very large int() (pythonGH-96504)

Converting between `int` and `str` in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now
raises a `ValueError` if the number of digits in string form is above a
limit to avoid potential denial of service attacks due to the algorithmic
complexity. This is a mitigation for CVE-2020-10735
(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735).

This new limit can be configured or disabled by environment variable, command
line flag, or :mod:`sys` APIs. See the `Integer String Conversion Length
Limitation` documentation.  The default limit is 4300
digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback
from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

Notes on the backport to Python 3.6:

* Use "Python 3.6.15-13" version in the documentation, whereas this
  version will never be released
* Only add _Py_global_config_int_max_str_digits global variable:
  Python 3.6 doesn't have PyConfig API (PEP 597) nor _PyRuntime.
* sys.flags.int_max_str_digits cannot be -1 on Python 3.6: it is
  set to the default limit. Adapt test_int_max_str_digits() for that.
* Declare _PY_LONG_DEFAULT_MAX_STR_DIGITS and
  _PY_LONG_MAX_STR_DIGITS_THRESHOLD macros in longobject.h but only
  if the Py_BUILD_CORE macro is defined.
* Declare _Py_global_config_int_max_str_digits in pydebug.h.

(cherry picked from commit 511ca94)

pythongh-95778: Mention sys.set_int_max_str_digits() in error message (python#96874)

When ValueError is raised if an integer is larger than the limit,
mention sys.set_int_max_str_digits() in the error message.

(cherry picked from commit e841ffc)

pythongh-96848: Fix -X int_max_str_digits option parsing (python#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with
no value (invalid) when the PYTHONINTMAXSTRDIGITS environment
variable is set to a valid limit.

(cherry picked from commit 4135166)
hroncok pushed a commit to fedora-python/cpython that referenced this pull request Jul 4, 2025
@vstinner @hroncok
00387: CVE-2020-10735: Prevent DoS by very large int()
e9711a4
pythongh-95778: CVE-2020-10735: Prevent DoS by very large int() (pythonGH-96504)

Converting between `int` and `str` in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now
raises a `ValueError` if the number of digits in string form is above a
limit to avoid potential denial of service attacks due to the algorithmic
complexity. This is a mitigation for CVE-2020-10735
(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735).

This new limit can be configured or disabled by environment variable, command
line flag, or :mod:`sys` APIs. See the `Integer String Conversion Length
Limitation` documentation.  The default limit is 4300
digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback
from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

Notes on the backport to Python 3.6:

* Use "Python 3.6.15-13" version in the documentation, whereas this
  version will never be released
* Only add _Py_global_config_int_max_str_digits global variable:
  Python 3.6 doesn't have PyConfig API (PEP 597) nor _PyRuntime.
* sys.flags.int_max_str_digits cannot be -1 on Python 3.6: it is
  set to the default limit. Adapt test_int_max_str_digits() for that.
* Declare _PY_LONG_DEFAULT_MAX_STR_DIGITS and
  _PY_LONG_MAX_STR_DIGITS_THRESHOLD macros in longobject.h but only
  if the Py_BUILD_CORE macro is defined.
* Declare _Py_global_config_int_max_str_digits in pydebug.h.

(cherry picked from commit 511ca94)

pythongh-95778: Mention sys.set_int_max_str_digits() in error message (python#96874)

When ValueError is raised if an integer is larger than the limit,
mention sys.set_int_max_str_digits() in the error message.

(cherry picked from commit e841ffc)

pythongh-96848: Fix -X int_max_str_digits option parsing (python#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with
no value (invalid) when the PYTHONINTMAXSTRDIGITS environment
variable is set to a valid limit.

(cherry picked from commit 4135166)
frenzymadness pushed a commit to fedora-python/cpython that referenced this pull request Aug 12, 2025
@vstinner @frenzymadness
00387: CVE-2020-10735: Prevent DoS by very large int()
8ca7e29
pythongh-95778: CVE-2020-10735: Prevent DoS by very large int() (pythonGH-96504)

Converting between `int` and `str` in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now
raises a `ValueError` if the number of digits in string form is above a
limit to avoid potential denial of service attacks due to the algorithmic
complexity. This is a mitigation for CVE-2020-10735
(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735).

This new limit can be configured or disabled by environment variable, command
line flag, or :mod:`sys` APIs. See the `Integer String Conversion Length
Limitation` documentation.  The default limit is 4300
digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback
from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

Notes on the backport to Python 3.6:

* Use "Python 3.6.15-13" version in the documentation, whereas this
  version will never be released
* Only add _Py_global_config_int_max_str_digits global variable:
  Python 3.6 doesn't have PyConfig API (PEP 597) nor _PyRuntime.
* sys.flags.int_max_str_digits cannot be -1 on Python 3.6: it is
  set to the default limit. Adapt test_int_max_str_digits() for that.
* Declare _PY_LONG_DEFAULT_MAX_STR_DIGITS and
  _PY_LONG_MAX_STR_DIGITS_THRESHOLD macros in longobject.h but only
  if the Py_BUILD_CORE macro is defined.
* Declare _Py_global_config_int_max_str_digits in pydebug.h.

(cherry picked from commit 511ca94)

pythongh-95778: Mention sys.set_int_max_str_digits() in error message (python#96874)

When ValueError is raised if an integer is larger than the limit,
mention sys.set_int_max_str_digits() in the error message.

(cherry picked from commit e841ffc)

pythongh-96848: Fix -X int_max_str_digits option parsing (python#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with
no value (invalid) when the PYTHONINTMAXSTRDIGITS environment
variable is set to a valid limit.

(cherry picked from commit 4135166)
hroncok pushed a commit to fedora-python/cpython that referenced this pull request Feb 3, 2026
@vstinner @hroncok
00387: CVE-2020-10735: Prevent DoS by very large int()
ad716c2
pythongh-95778: CVE-2020-10735: Prevent DoS by very large int() (pythonGH-96504)

Converting between `int` and `str` in bases other than 2
(binary), 4, 8 (octal), 16 (hexadecimal), or 32 such as base 10 (decimal) now
raises a `ValueError` if the number of digits in string form is above a
limit to avoid potential denial of service attacks due to the algorithmic
complexity. This is a mitigation for CVE-2020-10735
(https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10735).

This new limit can be configured or disabled by environment variable, command
line flag, or :mod:`sys` APIs. See the `Integer String Conversion Length
Limitation` documentation.  The default limit is 4300
digits in string form.

Patch by Gregory P. Smith [Google] and Christian Heimes [Red Hat] with feedback
from Victor Stinner, Thomas Wouters, Steve Dower, Ned Deily, and Mark Dickinson.

Notes on the backport to Python 3.6:

* Use "Python 3.6.15-13" version in the documentation, whereas this
  version will never be released
* Only add _Py_global_config_int_max_str_digits global variable:
  Python 3.6 doesn't have PyConfig API (PEP 597) nor _PyRuntime.
* sys.flags.int_max_str_digits cannot be -1 on Python 3.6: it is
  set to the default limit. Adapt test_int_max_str_digits() for that.
* Declare _PY_LONG_DEFAULT_MAX_STR_DIGITS and
  _PY_LONG_MAX_STR_DIGITS_THRESHOLD macros in longobject.h but only
  if the Py_BUILD_CORE macro is defined.
* Declare _Py_global_config_int_max_str_digits in pydebug.h.

(cherry picked from commit 511ca94)

pythongh-95778: Mention sys.set_int_max_str_digits() in error message (python#96874)

When ValueError is raised if an integer is larger than the limit,
mention sys.set_int_max_str_digits() in the error message.

(cherry picked from commit e841ffc)

pythongh-96848: Fix -X int_max_str_digits option parsing (python#96988)

Fix command line parsing: reject "-X int_max_str_digits" option with
no value (invalid) when the PYTHONINTMAXSTRDIGITS environment
variable is set to a valid limit.

(cherry picked from commit 4135166)
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