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.