ANT-2026-9R51NPJC · c-blosc2

heap-buffer-overflow high

Severity Claude high · Security research firm high · Maintainer -

Discovered by Claude Mythos Preview

REPORT

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

ANT-2026-9R51NPJC: Heap buffer overflow in NDLZ8 triple-match decompression due to unchecked row index

Heap buffer overflow in the NDLZ8 triple-match decompression path caused by an unchecked row index.

Target

Project: c-blosc2
Discovery: static analysis — not yet dynamically reproduced

Technical Details

During NDLZ8 decompression, the triple-match code path uses a row index without validating it against buffer bounds, resulting in out-of-bounds heap access.

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-2026-9R51NPJC.

Reference: ANT-2026-9R51NPJC
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: high

TIMELINE

Dates from discovery through public reveal.

2026-03-27 Sent to maintainer
2026-03-27 Patch released
2026-03-29 Reported to tracker
2026-05-09 Maintainer acknowledged
2026-08-17 Publicly revealed

PROVENANCE

SHA-3-512 hash:

90f1ff0a499f1395647c64f99a887b3ed3590bd3ea85d32bcc8c587c5ee7fb77cee7f783acf956258d1c497f47c8b9beb261a3eb00329bc73939cb4f7b8c6e40

Committed 2026-04-09 11:49 PT

Revealed 2026-08-17 13:02 PT

Verify (download preimage.json)

Show preimage JSON

{
  "ant_id": "ANT-2026-9R51NPJC",
  "bug_class": "Heap Buffer Overflow",
  "claude_severity": "high",
  "commit_sha": null,
  "created_at": "2026-03-29T20:42:40+00:00",
  "description": "Heap buffer overflow in the NDLZ8 triple-match decompression path caused by an unchecked row index.",
  "discovered_at": null,
  "location": null,
  "poc_sha256": null,
  "preimage_version": 1,
  "project": "c-blosc2",
  "reproduction": null,
  "technical_details": "During NDLZ8 decompression, the triple-match code path uses a row index without validating it against buffer bounds, resulting in out-of-bounds heap access.",
  "title": "Heap buffer overflow in NDLZ8 triple-match decompression due to unchecked row index",
  "vendor_severity": "high"
}