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

nimiq-block contains block primitives to be used in Nimiq's Rust implementation. `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. Prior to version 1.3.0, 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. The patch for this vulnerability is included as part of v1.3.0. No known workarounds are available.

Source published

22 Apr 2026 19:13:04 UTC

Source modified

23 Apr 2026 14:15:20 UTC

Observed here

23 Oct 2026 15:48:27 UTC

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CVSS 3.1 · 9.6 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:H