{"id":"GHSA-6973-8887-87ff","summary":"nimiq-block has skip block quorum bypass via out-of-range BitSet indices & u16 truncation","details":"### Impact\n`SkipBlockProof::verify` computes its quorum check using `BitSet.len()`, then iterates `BitSet` indices and casts each `usize` index to `u16` (`slot as u16`) for slot lookup. If an attacker can get a `SkipBlockProof` verified where `MultiSignature.signers` contains out-of-range indices spaced by 65536, these indices inflate `len()` but collide onto the same in-range `u16` slot during aggregation.\n\nThis makes it possible for a malicious validator with far fewer than `2f+1` real signer slots to pass skip block proof verification by multiplying a single BLS signature by the same factor.\n\n### Patches\n[The patch for this vulnerability](https://github.com/nimiq/core-rs-albatross/pull/3657) is included as part of [v1.3.0](https://github.com/nimiq/core-rs-albatross/releases/tag/v1.3.0).\n\n### Workarounds\nNo known workarounds.","aliases":["CVE-2026-33471"],"modified":"2026-05-05T16:02:38.268045Z","published":"2026-04-22T19:13:47Z","database_specific":{"github_reviewed_at":"2026-04-22T19:13:47Z","nvd_published_at":"2026-04-22T20:16:40Z","cwe_ids":["CWE-1284","CWE-190","CWE-20","CWE-345"],"severity":"CRITICAL","github_reviewed":true},"references":[{"type":"WEB","url":"https://github.com/nimiq/core-rs-albatross/security/advisories/GHSA-6973-8887-87ff"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-33471"},{"type":"WEB","url":"https://github.com/nimiq/core-rs-albatross/pull/3657"},{"type":"WEB","url":"https://github.com/nimiq/core-rs-albatross/commit/d02059053181ed8ddad6b59a0adfd661ef5cd823"},{"type":"PACKAGE","url":"https://github.com/nimiq/core-rs-albatross"},{"type":"WEB","url":"https://github.com/nimiq/core-rs-albatross/releases/tag/v1.3.0"}],"affected":[{"package":{"name":"nimiq-block","ecosystem":"crates.io","purl":"pkg:cargo/nimiq-block"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"last_affected":"0.2.0"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/04/GHSA-6973-8887-87ff/GHSA-6973-8887-87ff.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:H"}]}