pyOpenSSL DTLS cookie callback buffer overflow

CRITICAL 9.8CVE-2026-27459 · GHSA-5pwr-322w-8jr4 · PYSEC-2026-2269 · Published 18/03/2026 · updated 10/09/2026

Package	Affected versions	Patched versions
pyopenssl PyPI	`≥ 22.0.0, < 26.0.0`	`26.0.0`
pyopenssl pyopenssl	`≥ 22.0.0, < 26.0.0`	`26.0.0`

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.

NVD description

pyOpenSSL is a Python wrapper around the OpenSSL library. Starting in version 22.0.0 and prior to version 26.0.0, 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. Starting in version 26.0.0, cookie values that are too long are now rejected.

References

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