GHSA-6973-8887-87ff
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](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.
Are you affected?
Enter the version of the package you're using.
Affected packages
0No fixed version published yet for nimiq-block. Pin to a known-safe version or switch to an alternative.
References
- https://github.com/nimiq/core-rs-albatross/security/advisories/GHSA-6973-8887-87ff[WEB]
- https://nvd.nist.gov/vuln/detail/CVE-2026-33471[ADVISORY]
- https://github.com/nimiq/core-rs-albatross/pull/3657[WEB]
- https://github.com/nimiq/core-rs-albatross/commit/d02059053181ed8ddad6b59a0adfd661ef5cd823[WEB]
- https://github.com/nimiq/core-rs-albatross[PACKAGE]
- https://github.com/nimiq/core-rs-albatross/releases/tag/v1.3.0[WEB]