GHSA-6973-8887-87FF

Vulnerability from github – Published: 2026-04-22 19:13 – Updated: 2026-04-22 19:13
VLAI?
Summary
nimiq-block has skip block quorum bypass via out-of-range BitSet indices & u16 truncation
Details

Impact

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.

This 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.

Patches

The patch for this vulnerability is included as part of v1.3.0.

Workarounds

No known workarounds.

Severity ?
9.6 (Critical)
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:H
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{
  "affected": [
    {
      "package": {
        "ecosystem": "crates.io",
        "name": "nimiq-block"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "last_affected": "0.2.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-33471"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-190",
      "CWE-345",
      "CWE-1284"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-04-22T19:13:47Z",
    "nvd_published_at": null,
    "severity": "CRITICAL"
  },
  "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.",
  "id": "GHSA-6973-8887-87ff",
  "modified": "2026-04-22T19:13:47Z",
  "published": "2026-04-22T19:13:47Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/nimiq/core-rs-albatross/security/advisories/GHSA-6973-8887-87ff"
    },
    {
      "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"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "nimiq-block has skip block quorum bypass via out-of-range BitSet indices \u0026 u16 truncation"
}


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