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.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | pyopenssl | >= 0.14.0, < 26.0.0 | 26.0.0 |
References
- https://github.com/pyca/pyopenssl/blob/358cbf29c4e364c59930e53a270116249581eaa3/CHANGELOG.rst#L27
- https://github.com/pyca/pyopenssl/security/advisories/GHSA-vp96-hxj8-p424
- https://github.com/pyca/pyopenssl/commit/d41a814759a9fb49584ca8ab3f7295de49a85aa0
- https://nvd.nist.gov/vuln/detail/CVE-2026-27448
- https://github.com/pyca/pyopenssl
- CVSS vector
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U- Weakness (CWE)
CWE-636- Platform
- Python (PyPI)
- Package
pyopenssl- Disclosed
- 16.03.2026
- Updated
- 11.10.2026 15:17
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-2268 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-vp96-hxj8-p424 - CC BY 4.0
Vulnerability history: pyopenssl
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 5
- First → latest
- 09.2013 03.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 4
- Low 1
Disclosures per year
- 2017: 0
- 2018: 2
- 2019: 0
- 2020: 0
- 2021: 0
- 2022: 0
- 2023: 0
- 2024: 0
- 2025: 0
- 2026: 2
earlier: 1
-
pyOpenSSL allows TLS connection bypass via unhandled callback exception in set_tlsext_servername_callback this entry
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