medium5.3
CVE-2026-27448
pyOpenSSL allows TLS connection bypass via unhandled callback exception in set_tlsext_servername_callback
Impact
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.
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| pip | pyopenssl | >= 0.14.0, < 26.0.0 | 26.0.0 |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Pyopenssl | Pyopenssl | from 0.14 before 26.0.0 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/pyca/pyopenssl/blob/358cbf29c4e364c59930e53a270116249581eaa3/CHANGELOG.rst#L27
- https://github.com/pyca/pyopenssl/commit/d41a814759a9fb49584ca8ab3f7295de49a85aa0
- https://github.com/pyca/pyopenssl/security/advisories/GHSA-vp96-hxj8-p424
- https://github.com/advisories/GHSA-vp96-hxj8-p424
- https://nvd.nist.gov/vuln/detail/CVE-2026-27448