# CVE-2026-33471

## Summary

- **CVE ID:** CVE-2026-33471
- **Severity:** CRITICAL
- **CVSS Score:** 9.6 (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:H)
- **CWE:** CWE-20, CWE-190, CWE-345, CWE-1284
- **Published:** Apr 22, 2026
- **Last Modified:** Apr 22, 2026

## Description

nimiq/core-rs-albatross is a Rust implementation of the Nimiq Proof-of-Stake protocol based on the Albatross consensus algorithm. `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.

## Affected Products

- nimiq — core-rs-albatross (< 1.3.0)
- nimiq — nimiq-block (< 1.3.0)

## References

- [CNA](https://github.com/nimiq/core-rs-albatross/security/advisories/GHSA-6973-8887-87ff)
- [CNA](https://github.com/nimiq/core-rs-albatross/commit/d02059053181ed8ddad6b59a0adfd661ef5cd823)
- [CNA](https://github.com/nimiq/core-rs-albatross/releases/tag/v1.3.0)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.22%
- **EPSS Percentile:** 12.2

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-11._