pyOpenSSL allows TLS connection bypass via unhandled callback exception in set_tlsext_servername_callback
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.
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describes (1)
Related CVEs.
| ID | severity | exploitable | ||
|---|---|---|---|---|
| CVE-2026-27448US | medium5.3 | — | ||
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` ra… | ||||
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references
External citations — patches, advisories, analysis.
- https://github.com/pyca/pyopensslPACKAGE
- https://github.com/pyca/pyopenssl/blob/358cbf29c4e364c59930e53a270116249581eaa3/CHANGELOG.rst#L27WEB
- https://github.com/pyca/pyopenssl/commit/d41a814759a9fb49584ca8ab3f7295de49a85aa0WEB
- https://github.com/pyca/pyopenssl/security/advisories/GHSA-vp96-hxj8-p424WEB
- https://nvd.nist.gov/vuln/detail/CVE-2026-27448ADVISORY
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