ANT-2026-MHV0A2SD · freetype2

heap-buffer-overflow medium

Severity Claude medium · Security research firm medium · Maintainer -

Discovered by Claude Mythos Preview

REPORT

Anthropic's analysis, sealed at approval. Disclosure to the maintainer was performed by Trail of Bits.

ANT-2026-MHV0A2SD: Heap buffer overflow in Type 1 Multi-Master BuildCharArray via struct field corruption bypassing bounds check

Heap buffer overflow in Type 1 Multi-Master BuildCharArray where struct field corruption allows bypassing a bounds check.

Target

Project: freetype2
Location: BuildCharArray (Type 1 Multi-Master)
Discovery: static analysis — not yet dynamically reproduced

Technical Details

A struct field can be corrupted such that the bounds check guarding writes into the BuildCharArray is bypassed, allowing out-of-bounds heap writes during Type 1 Multi-Master font charstring interpretation.

Reproduction

This finding was identified by static analysis and has not yet been dynamically reproduced. The Technical Details section above describes the code path; a trigger input is not included.

[No reproducer or sanitizer output attached — request from security-cvd@anthropic.com if needed.]

Acknowledgement

This vulnerability was discovered by Claude, Anthropic's AI assistant, and triaged by the Anthropic security team in collaboration with Anthropic Research. Please direct questions to security-cvd@anthropic.com and reference ANT-2026-MHV0A2SD.

Reference: ANT-2026-MHV0A2SD
Anthropic CVD Policy: https://www.anthropic.com/coordinated-vulnerability-disclosure

SECURITY RESEARCH FIRM ANALYSIS

Triage and disclosure were performed by Trail of Bits.

Verdict
true positive
Severity
medium
TIMELINE

Dates from discovery through public reveal.

  1. 2026-03-21 Sent to maintainer
  2. 2026-03-22 Patch released
  3. 2026-03-29 Reported to tracker
  4. 2026-05-09 Maintainer acknowledged
  5. 2026-08-17 Publicly revealed
PROVENANCE

SHA-3-512 hash:

9d79a6e25b54371b04cb288170cb834ebc4e1a8a252c47277ce0386742a21844e7b508515d9365e459ac69b784159f4a44d5b9631223abc400c41c3593134ef1

Committed 2026-04-09 11:49 PT

Revealed 2026-08-17 13:02 PT

Verify (download preimage.json)

Show preimage JSON 
{
  "ant_id": "ANT-2026-MHV0A2SD",
  "bug_class": "Heap Buffer Overflow",
  "claude_severity": "medium",
  "commit_sha": null,
  "created_at": "2026-03-29T20:42:49+00:00",
  "description": "Heap buffer overflow in Type 1 Multi-Master BuildCharArray where struct field corruption allows bypassing a bounds check.",
  "discovered_at": null,
  "location": "BuildCharArray (Type 1 Multi-Master)",
  "poc_sha256": null,
  "preimage_version": 1,
  "project": "FreeType2",
  "reproduction": null,
  "technical_details": "A struct field can be corrupted such that the bounds check guarding writes into the BuildCharArray is bypassed, allowing out-of-bounds heap writes during Type 1 Multi-Master font charstring interpretation.",
  "title": "Heap buffer overflow in Type 1 Multi-Master BuildCharArray via struct field corruption bypassing bounds check",
  "vendor_severity": "medium"
}