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Fencer Vulns
medium 5.3

CVE-2026-27448 json

pyOpenSSL allows TLS connection bypass via unhandled callback exception in set_tlsext_servername_callback

published 2026-03-16 7 mo ago modified 2026-09-10 1 mo ago also EUVD-2026-12675 , GHSA-vp96-hxj8-p424 , PYSEC-2026-2268

cvss
5.3
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 17%
public exploits
0
none known

Summary

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.

Patch / fix

  • pypi pyopenssl 26.0.0
  • pyopenssl pyopenssl 26.0.0
  • pyopenssl Debian 13 25.0.0-1+deb13u1
  • pyopenssl Debian 14 26.0.0-1

debian advisories DEBIAN-CVE-2026-27448

  • pyopenssl Ubuntu 22.04 LTS 21.0.0-1ubuntu0.1
  • pyopenssl Ubuntu 24.04 LTS 23.2.0-1ubuntu0.1
  • pyopenssl Ubuntu 25.10 25.0.0-1ubuntu0.1
  • pyopenssl Ubuntu Pro 16.04 LTS 0.15.1-2ubuntu0.2+esm1
  • pyopenssl Ubuntu Pro 18.04 LTS 17.5.0-1ubuntu1+esm1
  • pyopenssl Ubuntu Pro 20.04 LTS 19.0.0-1ubuntu0.1~esm1

ubuntu advisories UBUNTU-CVE-2026-27448

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • pyOpenSSL hummingbird 1 26.0.0-1.1.hum1
  • python3-pyOpenSSL hummingbird 1 26.0.0-1.1.hum1

red hat advisories RHSA-2026:7224

  • python3-pyOpenSSL SLE Module for Basesystem 15 SP7, SLE Micro 5.5, SLE Micro 5.4 +1 more 21.0.0-150400.22.1
  • venv-salt-minion Multi Linux Manager Tools SLE-Micro-5, Multi Linux Manager Tools SLE-15 3006.0-150002.5.19.1
  • venv-salt-minion Manager Client Tools for RHEL, Liberty and Clones 9-CLIENT-TOOLS 3006.0-1.76.1
  • python-pyOpenSSL SLE Micro 5.2 19.0.0-150300.3.3.1
  • python-pyOpenSSL SLES for SAP 15 SP6, SLES for SAP 15 SP5, SLES for SAP 15 SP4 +10 more 23.2.0-150400.3.13.1
  • python-pyOpenSSL Linux Micro 6.0 24.0.0-2.1
  • python-pyOpenSSL Linux Micro 6.1 24.0.0-slfo.1.1_2.1
  • python-pyOpenSSL SLES for SAP applications 16.0, SLES 16.0 25.0.0-160000.3.1

suse advisories SUSE-SU-2026:3424-1SUSE-RU-2026:2769-1SUSE-EL-9-CLIENT-TOOLS-2026-2255SUSE-SU-2026:1582-1SUSE-SU-2026:1416-1SUSE-SU-2026:1192-1

  • python-pyOpenSSL openSUSE Leap 16.0 25.0.0-160000.3.1
  • python-pyOpenSSL openSUSE Tumbleweed 26.0.0-1.1

opensuse advisories openSUSE-SU-2026:20419-1openSUSE-SU-2026:10392-1

  • py3-openssl Alpine 3.24, Alpine 3.23 26.1.0-r0

alpine advisories ALPINE-CVE-2026-27448

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • pyOpenSSL Azure Linux 3.0 24.2.1-2

azure linux advisories AZL-80031

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-27448 updated cvss 5.4

pyOpenSSL: TLS connection bypass via unhandled callback exception in set_tlsext_servername_callback

  • Red Hat Ansible Automation Platform 2 python-pyOpenSSL, python3x-pyOpenSSL, python3.11-pyOpenSSL, python3.12-pyOpenSSL, automation-controller, ansible-automation-platform-26/hub-rhel9, +10 more Red Hat Ansible Automation Platform Ansible Core 2 ansible-automation-platform/ee-minimal-rhel8, ansible-automation-platform/ee-minimal-rhel9, ansible-automation-platform-tech-preview/ee-minimal-rhel8, ansible-automation-platform-tech-preview/ee-minimal-rhel9 Red Hat Enterprise Linux 8 python3-pyOpenSSL Red Hat OpenShift AI (RHOAI) rhoai/odh-mlflow-rhel9, rhoai/odh-feature-server-rhel9 Red Hat OpenShift Container Platform 4 pyOpenSSL Red Hat OpenStack Platform 17.1 python3-pyOpenSSL
    +5 more products
    Red Hat OpenStack Platform 18.0 pyOpenSSL Red Hat Quay 3 quay/quay-rhel8, quay/quay-rhel9 Red Hat Satellite 6 python-pyOpenSSL, python3-pyOpenSSL, python3.12-pyOpenSSL, satellite/iop-advisor-engine-rhel9, satellite/iop-insights-engine-rhel9 Red Hat Trusted Artifact Signer rhtas/model-transparency-rhel9 Red Hat Update Infrastructure 4 for Cloud Providers python-pyOpenSSL
    affected: workaround, no fix available “Fix deferred”
  • Red Hat Hardened Images pyOpenSSL 26.0.0-1.1.hum1, python3-pyOpenSSL 26.0.0-1.1.hum1
    fixed: vendor fix RHSA-2026:7224
  • Red Hat Enterprise Linux 6 pyOpenSSL Red Hat Enterprise Linux 7 pyOpenSSL
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
7 mo ago

Exploit prediction

0.26% chance of exploitation in the next 30 days, higher than 17% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 4.0 1.7 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
CNA 4.0 1.7 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:X/V:X/RE:X/U:X
NVD 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
OSV 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Affected packages

ecosystem package affected fixed in
pypi pyopenssl
>=0.14.0, <26.0.0
>=0.14, <26.0.0
26.0.0

Affected products

  • pyca pyopenssl

Classification

Weakness

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.