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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

9.6 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:H

EPSS

• CVE-2026-33471: 0.22% estimated exploitation activity in the next 30 days; percentile 12.28 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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.

Published by the source

22 Apr 2026, 19:13 UTC

Last modified by the source

30 Oct 2026, 15:45 UTC

Source last checked

31 Oct 2026, 06:45 UTC

1. Revision 2 · amended · 31 Oct 2026

   Amended from osv record GHSA-6973-8887-87ff

2. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-6973-8887-87ff

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# Patch Next advisory brief: CVE-2026-33471

Advisory: nimiq-block has skip block quorum bypass via out-of-range BitSet indices & u16 truncation
IDs: CVE-2026-33471, GHSA-6973-8887-87ff
Record: https://patchnext.com/advisories/cve-2026-33471 (revision 2, source checked 31 Oct 2026, 06:45 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.6)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: nimiq-block 1.7.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io nimiq-block: affected < 1.7.2; fixed in 1.7.2

## Suggested inspection (read-only)
- crates.io nimiq-block: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on nimiq-block.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-6973-8887-87ff (GitHub-reviewed advisory GHSA-6973-8887-87ff lists affected ranges: crates.io nimiq-block >=0 <=0.2.0)
- Verified: https://osv.dev/vulnerability/GHSA-6973-8887-87ff (OSV record GHSA-6973-8887-87ff lists affected ranges: crates.io nimiq-block >=0 <1.7.2 (fixed))

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