# CVE-2026-33471

> Vulnerability · severity: **CRITICAL** (CVSS 9.6).

## Description

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.

## Key facts

- **CVE ID:** CVE-2026-33471
- **Published:** 2026-04-22
- **CVSS severity:** CRITICAL
- **CVSS base score:** 9.6
- **CWE codes:** CWE-20, CWE-190, CWE-345, CWE-1284

## Affected products

- `nimiq:nimiq_proof-of-stake`

## Primary sources

- NIST NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-33471

## Citation

> AI Analytics. CVE-2026-33471. Retrieved 2026-07-23 from https://api.ai-analytics.org/cve/CVE-2026-33471. Derived from NIST NVD. Licensed CC0.

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