email.utils.parseaddr() and getaddresses(), even in strict=True mode (the default since the CVE-2023-27043 fix), silently drop a comment that is embedded inside a dot-atom and splice the surrounding atoms together:

>>> from email.utils import parseaddr
>>> parseaddr('u(comment)[email protected]', strict=True)
('comment comment', '[email protected]')

The strict parser rejects the same input:

>>> from email.headerregistry import Address
>>> Address(addr_spec='u(comment)[email protected]')
InvalidHeaderDefect: local-part is not dot-atom, quoted-string, or obs-local-part

So a caller that validates or authorizes with parseaddr and then hands the original string to a strict component gets a subject mismatch — the same class as CVE-2019-11340 and the motivation for CVE-2023-27043.

Proposal: in strict mode, fail closed (return ('', '')) when a comment is embedded inside a dot-atom instead of splicing. strict=False would keep the historical lenient behavior. I'm happy to prepare a PR.

Reproduced on CPython 3.14.6.

Linked PRs

• gh-159475: Make parseaddr() reject inline comments in strict mode #159477
• gh-159475: Make parseaddr() reject inline comments in strict mode #159618