ANT-2026-DD4RKCBA · opensc

stack-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-DD4RKCBA: Stack buffer overflow in asn1_encode_p15_object access rules loop due to array index exceeding bounds

The access rules loop in asn1_encode_p15_object allows the array index to exceed bounds, causing a stack buffer overflow.

Target

Project: opensc
Location: asn1_encode_p15_object()
Discovery: static analysis — not yet dynamically reproduced

Technical Details

The loop iterating over access rules in asn1_encode_p15_object does not correctly bound the array index, resulting in writes past the end of a stack-allocated buffer.

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-DD4RKCBA.

Reference: ANT-2026-DD4RKCBA
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. 2026-03-25 Sent to maintainer
  2. 2026-03-29 Reported to tracker
  3. 2026-03-29 Patch released
  4. 2026-05-09 Maintainer acknowledged
  5. 2026-08-17 Publicly revealed
PROVENANCE

SHA-3-512 hash:

51b7525cf6d947bd4ae6bc104f1abfe6e48bafc192b8637d618f4ec408a51a2eda57bcc7aac6aa75df82cca2d785620e665d1722dc865b4d74f9fd9bdad38f65

Committed 2026-04-09 11:50 PT

Revealed 2026-08-17 13:03 PT

Verify (download preimage.json)

Show preimage JSON 
{
  "ant_id": "ANT-2026-DD4RKCBA",
  "bug_class": "Stack Buffer Overflow",
  "claude_severity": "medium",
  "commit_sha": null,
  "created_at": "2026-03-29T20:43:22+00:00",
  "description": "The access rules loop in asn1_encode_p15_object allows the array index to exceed bounds, causing a stack buffer overflow.",
  "discovered_at": null,
  "location": "asn1_encode_p15_object()",
  "poc_sha256": null,
  "preimage_version": 1,
  "project": "OpenSC",
  "reproduction": null,
  "technical_details": "The loop iterating over access rules in asn1_encode_p15_object does not correctly bound the array index, resulting in writes past the end of a stack-allocated buffer.",
  "title": "Stack buffer overflow in asn1_encode_p15_object access rules loop due to array index exceeding bounds",
  "vendor_severity": "medium"
}