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

CVE-2026-33471 → View on GitHub ↗ View on CVE.org ↗ View on NVD ↗

Description

Impact

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. 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.

Patches

The patch for this vulnerability is included as part of v1.3.0.

Workarounds

No known workarounds.

Basic information

Type
reviewed
Severity
critical
Advisory on GitHub
Open advisory ↗
Repository advisory
Open repository advisory ↗
Source code
Browse source ↗
Published (advisory)
2026-04-22 19:13:47 UTC
Updated
2026-04-27 16:22:05 UTC
GitHub reviewed
2026-04-22 19:13:47 UTC
NVD published
2026-04-22 20:16:40 UTC

EPSS Score

Score Percentile
0.03% 8.62%

CVSS Scores

Base score Version Severity Vector
9.6 3.1 —
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.

Identifiers

Type Value
GHSA GHSA-6973-8887-87ff ↗
CVE CVE-2026-33471 ↗

CWEs

CWE id Name
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

Credits

  • 1seal (finder)

Affected packages (1)

Vulnerable version ranges and first patched releases as published by GitHub.

Ecosystem Package Vulnerable range First patched Vulnerable functions
rust nimiq-block <= 0.2.0 — —

References

cvelogic Threat Intelligence