CVE-2026-3644: Python

High severity, CVSS 7.5. EPSS: 0.5% chance of exploitation in the next 30 days.

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().

Affected products

• Python Python: before 3.13.13 (fixed in 3.13.13); from 3.14.0, before 3.14.4 (fixed in 3.14.4); version 3.15.0 only

Published 2026-03-16. Last modified 2026-08-13.