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CVE-2026-27448 — pyOpenSSL allows TLS connection bypass via unhandled callback exception in set_tlsext_servername_callback

2026-09-30T18:05:42.813618+00:00

Affected: pyca pyopenssl

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.

GHSA-vp96-hxj8-p424 — pyOpenSSL allows TLS connection bypass via unhandled callback exception in set_tlsext_servername_callback

2026-09-30T18:05:42.813706+00:00

Affected: PyPI: pyopenssl

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.

Unhandled exceptions now result in rejecting the connection.

Credit to **Leury Castillo** for reporting this issue.

PYSEC-2026-2268

2026-09-30T18:05:42.813751+00:00

Affected: PyPI: pyopenssl