feat: AVE-2026-00074 -- reclaimable dead external anchor (SkillJacking)

[chaksaray]

Summary

• Adds AVE-2026-00074: a skill references an external GitHub owner/repo, package, domain, or cloud subdomain that was live and under its original owner's control when authored, but has since been deleted, renamed, or expired -- making it re-registerable by an attacker with no change to the skill's own committed content.
• Distinct from AVE-2026-00062 (unpinned dependency substitution): 00062's mechanism is the absence of a pin from the moment a reference was declared. Here the reference may have been fully precise and stable when written -- pinning would not have helped, because the vulnerability is a previously-resolved reference whose target identity changed out from under it after publication, not an unresolved one.
• Verified via keyword sweep against the live corpus (no match), field-level comparison of provenance_vector against AVE-2026-00062 (genuinely distinct mechanism), and by reading the actual repo-forensics scanner source, not just its README:
  • Primary source: alexgreensh/repo-forensics scan_dead_anchors.py -- extracts every external anchor a skill points at and probes whether it's confirmed-claimable, live-and-owned, or unverifiable.
  • Independent real-world confirmation: AIR Security's SkillJacking disclosure (2026-07-02) -- 925 skills / ~134,000 agents found on hijackable dependencies, including a confirmed takeover of the seedance2-api skill (11,483 installs) via re-registering its deleted GitHub owner.
• Severity HIGH, AIVSS 7.1 (cvss_base 8.7, aars 5.5 -- dynamic_identity scored at genuine maximum, this class is definitionally trust-anchor confusion).
• mitre_atlas researched and left empty rather than force-fit: ATLAS's own AI-software supply-chain technique (AML.T0010.001) names build/maintainer compromise, namesquatting, and hallucinated package names as its sub-cases -- none name an attacker legitimately re-registering an identity the original owner abandoned. A genuine gap in ATLAS's own taxonomy.

Test plan

• python3 scripts/validate_records.py -- 74/74 records valid
• python3 scripts/check_fixtures.py -- all records have positive + negative fixtures
• pytest tests/ -x -q -- 297 passed
• node scripts/build-records.js -- dist regenerated, frozen v1.1.0 snapshot untouched
• README record count (badge, Stats table, collapsible index) and CHANGELOG updated