CVE-2026-27459

CRITICAL9.8EPSS 0.03%

pyOpenSSL DTLS cookie callback buffer overflow

Published: 3/16/2026Modified: 5/11/2026

Also known as:GHSA-5pwr-322w-8jr4CGA-qv3q-jpxp-cpmx

Description

If a user provided callback to `set_cookie_generate_callback` returned a cookie value greater than 256 bytes, pyOpenSSL would overflow an OpenSSL provided buffer. Cookie values that are too long are now rejected.

Affected packages (2)

Debian/pyopensslfrom 0
PyPI/pyopenssl>= 22.0.0, < 26.0.0

CVSS scores

Source	Version	Severity	Vector
osv	CVSS 4.0	—	CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U
osv	CVSS 3.1	CRITICAL9.8	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

References (6)

ADVISORYhttps://nvd.nist.gov/vuln/detail/CVE-2026-27459
ADVISORYhttps://security-tracker.debian.org/tracker/CVE-2026-27459
PATCHhttps://github.com/pyca/pyopenssl
WEBhttps://github.com/pyca/pyopenssl/blob/358cbf29c4e364c59930e53a270116249581eaa3/CHANGELOG.rst
WEBhttps://github.com/pyca/pyopenssl/commit/57f09bb4bb051d3bc2a1abd36e9525313d5cd408
WEBhttps://github.com/pyca/pyopenssl/security/advisories/GHSA-5pwr-322w-8jr4