CVE-2026-27459: pyOpenSSL DTLS cookie callback buffer overflow
If a user provided callback to setcookiegeneratecallback returned a cookie value greater than 256 bytes, pyOpenSSL would overflow an OpenSSL provided buffer.
Cookie values that are too long are now rejected.
Other sources
pyOpenSSL DTLS cookie callback buffer overflow
— Microsoft
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 setcookiegeneratecallback 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.
— NVD
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
pip/pyopensslto a version that resolves this vulnerability.Fixed in 26.0.0 - Upgrade
Upgrade
pyOpenSSLto a version that resolves this vulnerability.Fixed in 26.0.0
Event History
Frequently Asked Questions
What is the severity of CVE-2026-27459?
CVE-2026-27459 has been rated as a medium severity vulnerability due to the potential for a buffer overflow.
How do I fix CVE-2026-27459?
To fix CVE-2026-27459, upgrade pyOpenSSL to version 26.0.0 or later.
What causes the CVE-2026-27459 vulnerability?
CVE-2026-27459 is caused by a user-provided callback that returns a cookie value greater than 256 bytes, leading to buffer overflow.
Which versions of pyOpenSSL are affected by CVE-2026-27459?
Affected versions of pyOpenSSL are those between 22.0.0 and 26.0.0, inclusive.
Is CVE-2026-27459 a remote code execution vulnerability?
CVE-2026-27459 does not lead to remote code execution but may allow denial-of-service through a buffer overflow.