CVE-2026-3644 Incomplete control character validation in http.cookies

Medium 6.0 Published 16 Mar 2026 Updated 13 Aug 2026

Incomplete control character validation in Python's http.cookies module allows bypassing input checks, potentially leading to header injection or parsing issues.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Over the internet
Victim action needed: Not needed
Fix: Available

What is CVE-2026-3644?

CVE-2026-3644 is a medium-severity vulnerability in Python Python, published on 16 Mar 2026. Any signed-in user can exploit it over the network, with no action from the victim.

Official description

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().

Weakness: CWE-20, CWE-116

Which versions are affected by CVE-2026-3644?

It affects 1 product.

Products include Python Python.

How do I fix CVE-2026-3644?

Apply the vendor's patch.

Is CVE-2026-3644 being exploited?

There is no known exploitation of CVE-2026-3644 in the wild and no public exploit code.

All Python Python vulnerabilities

Sources

Also known as ALPINE-CVE-2026-3644, AZL-109704, AZL-80055, BELL-CVE-2026-3644, DEBIAN-CVE-2026-3644, ECHO-6a47-d40a-2c76 and 10 more.