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🐍 PyPI
Not in CISA KEV
HIGH severity

CVE-2013-4314 — pyopenssl

HIGHFix: pyca/pyopenssl@6bbf44a

CVE-2013-4314 is a high-severity (CVSS 7.5) Improper Input Validation vulnerability in pyopenssl. A fix is available for pyopenssl — see the affected versions and patch details below.

PyOpenSSL Mishandles NUL Byte In Certificate Subject Alternative Name

Also known asGHSA-6748-36qp-fx6rPYSEC-2013-31
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Nov 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
1.2%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs68th percentile — riskier than 68% of all scored CVEsHighest risk
0.00%0.57%1.13%1.70%0.3%1.2%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected
🐍pyopenssl

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

The X509Extension in pyOpenSSL before 0.13.1 does not properly handle a '\0' character in a domain name in the Subject Alternative Name field of an X.509 certificate, which allows man-in-the-middle attackers to spoof arbitrary SSL servers via a crafted certificate issued by a legitimate Certification Authority.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐍PyPIpyopensslall versions0.13.1pip install --upgrade 'pyopenssl==0.13.1'

Affected Products

2 products · 13 configurations
OS
ubuntu linuxcanonical
4 versions
10.0412.0412.1013.04
Application
pyopenssljean-paul_calderone
≤ 0.13
6 versions
0.70.80.90.100.110.12

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for pyopenssl, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update pyopenssl to 0.13.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2013-4314 is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

The X509Extension in pyOpenSSL before 0.13.1 does not properly handle a '\0' character in a domain name in the Subject Alternative Name field of an X.509 certificate, which allows man-in-the-middle attackers to spoof arbitrary SSL servers via a crafted certificate issued by a legitimate Certification Authority.
O3 Security · Impact-Aware SCA

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CVE-2013-4314: pyopenssl — Fixed in 0.13.1