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Vulnerability · Published Mar 17, 2026 · Assigned by GitHub_M

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

Low 1.7

In plain English

A low-severity security flaw in pyopenssl from pyca. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 17% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 4.0)1.7Low
Exploit odds (30 days)0.3%top 82.7% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Alpine:v3.23py3-openssl26.1.0-r0ALPINE-CVE-2026-27448
Alpine:v3.24py3-openssl26.1.0-r0ALPINE-CVE-2026-27448
Debian:12pyopensslno fix listedDEBIAN-CVE-2026-27448
Debian:13pyopenssl25.0.0-1+deb13u1DEBIAN-CVE-2026-27448
Debian:14pyopenssl26.0.0-1DEBIAN-CVE-2026-27448
PyPIpyopenssl26.0.0PYSEC-2026-2268
PyPIpyopenssl26.0.0GHSA-vp96-hxj8-p424
Ubuntu:22.04:LTSpyopenssl21.0.0-1ubuntu0.1UBUNTU-CVE-2026-27448
Ubuntu:24.04:LTSpyopenssl23.2.0-1ubuntu0.1UBUNTU-CVE-2026-27448
Ubuntu:25.10pyopenssl25.0.0-1ubuntu0.1UBUNTU-CVE-2026-27448

Affected products (as reported)

VendorProductVersions
pyca pyopenssl >= 0.14.0, < 26.0.0

Weakness: CWE-636 · 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

References