critical · 9.6 Patched

nimiq-block has skip block quorum bypass via out-of-range BitSet indices & u16 truncation

CVE-2026-33471 · GHSA-6973-8887-87ff · published 22 Apr 2026

How serious is it

  • Severity: critical, CVSS score 9.6 out of 10.
  • No exploit prediction (EPSS) score yet.
  • Not on the CISA list of exploited vulnerabilities.
  • No public exploit in Exploit-DB.

Is your app affected by CVE-2026-33471?

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Who is affected

  • nimiq-block (crates.io) < 1.3.0

How to check

  1. Run cargo tree -i nimiq-block in your project to see the installed version, including copies pulled in by other packages.
  2. Or paste your lockfile into the checker: it lists every package with a known vulnerability, this one included.

How to fix

Copies a prompt for Claude Code, Cursor or Codex: it checks your lockfiles for this and upgrades it.
  1. Upgrade nimiq-block to 1.7.2 or later, commit the lockfile and redeploy.
  2. If a vulnerable version was live, check your logs and rotate the secrets that server could read.

The advisory

### 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](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). ### Workarounds No known workarounds.

Check your whole app

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References

Merged from GitHub Advisory Database, OSV. Last updated 31 Oct 2026. All vulnerabilities · RSS · JSON

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