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CVE-2026-0865VulnerabilityPublished Updated

CVE-2026-0865: Python Software Foundation CPython · Injection

Affects Python Software Foundation CPythonSource CVE Database V5

0

Not known to be exploited · CVSS 5.9 Medium · fixed in 3.15.0a6 : update Python Software Foundation CPython when convenient.

Data as of 26 Oct 2026, 06:26 UTC

CVSS 4.0 base score
5.9Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.5% chance of exploitation in 30 days – higher than 46% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 3.15.0a6, 3.14.3, 3.13.12 +3
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

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 20 Jan 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 2026-10-26.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

ProductAffectedFixed in
Python Software FoundationCPythonAffected
  • <3.10.20
  • >=3.11.0 <3.11.15
  • >=3.12.0 <3.12.13
  • >=3.13.0 <3.13.12
  • >=3.14.0 <3.14.3
  • >=3.15.0a1 <3.15.0a6
Fixed in
  • 3.15.0a6
  • 3.14.3
  • 3.13.12
  • 3.12.13
  • 3.11.15
  • 3.10.20
GitHubpython/cpythonpkg:github/python/cpythonOther threatsAffected
  • =0
  • =3.11.0
  • =3.12.0
  • =3.13.0
  • =3.14.0
  • =3.15.0
Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

To mitigate CVE-2026-0865, organizations should promptly upgrade to a CPython version where this vulnerability is patched once available. Until then, implement strict input validation and sanitization on all user-supplied HTTP header names and values to reject or escape newline and other control characters that could enable header injection. Employ web application firewalls (WAFs) with rules designed to detect and block HTTP header injection attempts. Review and harden any custom HTTP header processing code to ensure it does not trust user input blindly. Additionally, limit the privileges of accounts that can send or modify HTTP headers to reduce the risk of exploitation. Monitor logs for suspicious header anomalies indicative of injection attempts. For Python web frameworks or libraries built on CPython, verify that they have incorporated patches or mitigations against this vulnerability. Finally, conduct security testing focused on HTTP header injection to identify and remediate vulnerable endpoints.

Description

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

References

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