ANT-2026-Z477W54M · cisco-talos/clamav

integer-underflow high

CVE-2026-20214 GHSA-86w7-h9x4-hpxv

Severity Claude high · Security research firm high · Maintainer high

Discovered by Claude Mythos Preview

REPORT

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

ANT-2026-Z477W54M: Unsigned integer underflow in FSG unpacker section loop

An unsigned integer underflow occurs in the section-processing loop of the FSG unpacker.

Target

Project: ClamAV
Location: libclamav/pe.c:cli_scanpe (FSG v1.31 unpacker handler, ~line 3719; loop boundt <= (uint32_t)sectcnt - 1underflows when sectcnt == 0)
Discovery: static analysis — not yet dynamically reproduced

Reproduction

This finding was identified by static analysis and has not yet been dynamically reproduced. 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-Z477W54M.

Reference: ANT-2026-Z477W54M
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
ADVISORY

https://github.com/Cisco-Talos/clamav/commit/9532b0687a8d6b66bb32c1d0b51ff0430750457b

TIMELINE

Dates from discovery through public reveal.

  1. 2026-03-29 Reported to tracker
  2. 2026-04-09 Sent to maintainer
  3. 2026-05-07 Patch released
  4. 2026-05-07 Maintainer acknowledged
  5. 2026-07-20 Publicly revealed
PROVENANCE

SHA-3-512 hash:

b8d4f660d79e46e525130fe4e10aa0281ee8404f73ca7f2fab23c7a483daff0d3a43e95658d1dcff1c1fc185fa140cf659fca6b1aa652064829afd28bbbd8f35

Committed 2026-04-09 11:49 PT

Revealed 2026-07-20 22:20 PT

Verify (download preimage.json)

Show preimage JSON 
{
  "ant_id": "ANT-2026-Z477W54M",
  "bug_class": "Integer Underflow",
  "claude_severity": "high",
  "commit_sha": null,
  "created_at": "2026-03-29T20:42:42+00:00",
  "description": "An unsigned integer underflow occurs in the section-processing loop of the FSG unpacker.",
  "discovered_at": null,
  "location": null,
  "poc_sha256": null,
  "preimage_version": 1,
  "project": "ClamAV",
  "reproduction": null,
  "technical_details": null,
  "title": "Unsigned integer underflow in FSG unpacker section loop",
  "vendor_severity": "high"
}