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Fencer Vulns
critical 9.6

CVE-2026-33471 json

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

published 2026-04-22 6 mo ago modified 2026-10-30 10 d ago also GHSA-6973-8887-87ff , EUVD-2026-25054

cvss
9.6
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 12%
public exploits
0
none known

Summary

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.

Patch / fix

  • crates.io nimiq-block 1.7.2
  • nimiq nimiq_proof-of-stake 1.3.0

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
6 mo ago

Exploit prediction

0.22% chance of exploitation in the next 30 days, higher than 12% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 9.6 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:H
GitHub 3.1 9.6 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:H

Affected packages

ecosystem package affected fixed in
crates.io nimiq-block
<1.7.2
1.7.2

Affected products

  • nimiq nimiq-block

Classification

Weakness
  • CWE-20 Improper Input Validation
  • CWE-190 Integer Overflow or Wraparound
  • CWE-345 Insufficient Verification of Data Authenticity
  • CWE-1284 Improper Validation of Specified Quantity in Input

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.