ANT-2026-8FZYKRTH · libreoffice

heap-buffer-overflow medium

CVE-2026-6039

Severity Claude high · Security research firm high · Maintainer medium

Discovered by Claude Mythos Preview

REPORT

Anthropic's analysis, sealed at approval. Disclosure to the maintainer was performed by Ada Logics.

ANT-2026-8FZYKRTH: Heap buffer overflow in DXF LWPOLYLINE import via integer truncation from sal_Int32 to sal_uInt16

Integer truncation from sal_Int32 to sal_uInt16 during DXF LWPOLYLINE import causes a heap buffer overflow.

Target

Project: libreoffice
Location: vcl/source/filter/idxf/dxf2mtf.cxx:DXF2GDIMetaFile::DrawLWPolyLineEntity
Discovery: static analysis — not yet dynamically reproduced

Technical Details

A 32-bit value (sal_Int32) is truncated to 16 bits (sal_uInt16) when handling an LWPOLYLINE entity in the DXF importer; the truncated value leads to an undersized buffer and a subsequent out-of-bounds heap write.

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-2026-8FZYKRTH.

Reference: ANT-2026-8FZYKRTH
Anthropic CVD Policy: https://www.anthropic.com/coordinated-vulnerability-disclosure

SECURITY RESEARCH FIRM ANALYSIS

Triage and disclosure were performed by Ada Logics.

Verdict: true positive
Severity: high

TIMELINE

Dates from discovery through public reveal.

2026-03-29 Reported to tracker
2026-04-09 Sent to maintainer
2026-04-29 Patch released
2026-05-09 Maintainer acknowledged
2026-08-17 Publicly revealed

PROVENANCE

SHA-3-512 hash:

a287adfa390e0cfcb2b267c2e1ff26b4a8e73b07532dafeed696cb0231a0d164d594559df99d67b8a195d5cd0549220922038fc2f119d3c5596945ae93fa5b44

Committed 2026-04-09 11:50 PT

Revealed 2026-08-17 14:12 PT

Verify (download preimage.json)

Show preimage JSON

{
  "ant_id": "ANT-2026-8FZYKRTH",
  "bug_class": "Heap Buffer Overflow",
  "claude_severity": "high",
  "commit_sha": null,
  "created_at": "2026-03-29T20:43:11+00:00",
  "description": "Integer truncation from sal_Int32 to sal_uInt16 during DXF LWPOLYLINE import causes a heap buffer overflow.",
  "discovered_at": null,
  "location": null,
  "poc_sha256": null,
  "preimage_version": 1,
  "project": "LibreOffice",
  "reproduction": null,
  "technical_details": "A 32-bit value (sal_Int32) is truncated to 16 bits (sal_uInt16) when handling an LWPOLYLINE entity in the DXF importer; the truncated value leads to an undersized buffer and a subsequent out-of-bounds heap write.",
  "title": "Heap buffer overflow in DXF LWPOLYLINE import via integer truncation from sal_Int32 to sal_uInt16",
  "vendor_severity": "high"
}