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Vulnerability record · CVE-2026-27448 · published 18 March 2026

CVE-2026-27448: Pyopenssl vulnerability

Pyopenssl · 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.

1.7 CVSS 4.0 Low EPSS 0.39% · top 69.4% CWE-636 · CWE-636
1.7CVSS 4.0 base score
0.39%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
3References
17 Jun 2026Last modified by NVD

Description

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.

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/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/pyca/pyopenssl/blob/358cbf29c4e364c59930e53a270116249581eaa3/CHANGELOG.rst#L27 Release Notes
https://github.com/pyca/pyopenssl/commit/d41a814759a9fb49584ca8ab3f7295de49a85aa0 Patch
https://github.com/pyca/pyopenssl/security/advisories/GHSA-vp96-hxj8-p424 Vendor Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

8.1CVE-2018-1000807Pyopenssl use after free vulnerabilityPython Cryptographic Authority pyopenssl version prior to version 17.5.0 contains a CWE-416: Use After Free vulnerability in X509 object handling tha…EPSS 4.1%7.2CVE-2026-27459Pyopenssl classic buffer overflow vulnerabilitypyOpenSSL is a Python wrapper around the OpenSSL library. Starting in version 22.0.0 and prior to version 26.0.0, if a user provided callback to `set…EPSS 0.88%

Source: NIST National Vulnerability Database (record CVE-2026-27448), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.