What’s Vulnerable › Vulnerabilities

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

• Severity: medium (CVSS 5.9 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-01-20 · updated 2026-06-17
• Weakness: CWE-74

Description

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

Affected products

• Python: before 3.10.20; from 3.11.0 before 3.11.15; from 3.12.0 before 3.12.13; from 3.13.0 before 3.13.12; from 3.14.0 before 3.14.3; from 3.15.0a1 before 3.15.0a6 — fixed in 3.10.20, 3.11.15, 3.12.13, 3.13.12, 3.14.3, 3.15.0a6

How to fix

Upgrade to a fixed version: Python 3.10.20, 3.11.15, 3.12.13, 3.13.12. Check the vendor advisory for mitigations.

References

• https://github.com/python/cpython/commit/22e4d55285cee52bc4dbe061324e5f30bd4dee58
• https://github.com/python/cpython/commit/23e3c0ae867cca0130e441e776c9955b9027c510
• https://github.com/python/cpython/commit/286e3ac39984fe85a17f4ab39c64d382137aae5f
• https://github.com/python/cpython/commit/2f840249550e082dc351743f474ba56da10478d2
• https://github.com/python/cpython/commit/4802b96a2cde58570c24c13ef3289490980961c5
• https://github.com/python/cpython/commit/66da7bf6fe7b81e3ecc9c0a25bd47d4616c8d1a6
• https://github.com/python/cpython/commit/83ecd18779f286d872f68bfce175651e407d9fff
• https://github.com/python/cpython/commit/8bb044d29310bb05d15086cdaa8bf64867d61a97
• https://github.com/python/cpython/commit/bfba660085767f8c2d582134e9d511a85eda04cf
• https://github.com/python/cpython/commit/c592227ffb48679af9845a45dbb0875d975bb219
• https://github.com/python/cpython/commit/e4846a93ac07a8ae9aa18203af0dd13d6e7a6995
• https://github.com/python/cpython/commit/f7fceed79ca1bceae8dbe5ba5bc8928564da7211

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