Input Validation Issue in Python's Cookie Handling
CVE-2026-3644

6MEDIUM

Key Information:

Vendor

Python Software Foundation

Status
Cpython
Vendor
CVE Published:
16 March 2026

What is CVE-2026-3644?

An incomplete fix for a previous vulnerability has resulted in an input validation issue within Python's handling of cookie data. Specifically, the Morsel.update() method and certain unpickling paths are missing necessary protections, allowing control characters to bypass validation. Additionally, the output validation for BaseCookie.js_output() has not been aligned with the safeguards present in BaseCookie.output(), potentially leading to security risks.

Affected Version(s)

CPython 0 < 3.13.13

CPython 3.14.0 < 3.14.4

CPython 3.15.0a1 < 3.15.0a8

References

https://mail.python.org/archives/list/security-announce@p...
vendor-advisory
https://github.com/python/cpython/commit/57e88c1cf95e1481...
patch
https://github.com/python/cpython/issues/145599
issue-tracking

CVSS V4

Score:
6
Severity:
MEDIUM
Confidentiality:
Low
Integrity:
High
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
Physical
Privileges Required:
Undefined
User Interaction:
None

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Stan Ulbrych
Stan Ulbrych
Victor Stinner
Seth Larson
Vyom Yadav
.