CVE-2026-27448: Pyopenssl

Medium severity, CVSS 5.3. EPSS: 0.4% chance of exploitation in the next 30 days.

pyOpenSSL is a Python wrapper around the OpenSSL library. Starting in version 0.14.0 and prior to version 26.0.0, if a user provided callback to `set_tlsext_servername_callback` raised an unhandled exception, this would result in a connection being accepted. If a user was relying on this callback for any security-sensitive behavior, this could allow bypassing it. Starting in version 26.0.0, unhandled exceptions now result in rejecting the connection.

Affected products

• Pyopenssl Pyopenssl: from 0.14, before 26.0.0 (fixed in 26.0.0)

Published 2026-03-18. Last modified 2026-06-17.