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CVE-2026-33471

Nimiq Proof-of-stake integer overflow

9.6 CRITICALEPSS 0.29%
  1. Published22 Apr 2026

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.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredLow
User interactionNone
ScopeChanged
ConfidentialityNone
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:H

Affected products

Nimiq Proof-of-stake< 1.3.0

Remediation

Fixed in
Nimiq Proof-of-stake≥ 1.3.0

References

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Frequently asked

Is CVE-2026-33471 being actively exploited?

CVE-2026-33471 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.29%.

How severe is CVE-2026-33471?

CVE-2026-33471 has a CVSS 3.1 base score of 9.6, rated critical. EPSS estimates a 0.29% probability of exploitation.

Which products are affected by CVE-2026-33471?

Affected products include Nimiq Proof-of-stake.

How do I fix CVE-2026-33471?

Upgrade affected software to a fixed version, for example Nimiq Proof-of-stake 1.3.0 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.