CVE-2026-33471: Nimiq block Nimiq-block Has Skip Block Quorum Vulnerability

CRITICAL
Advisory Identifier: GHSA-6973-8887-87ff
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CVSS 9.6
CWE-190 CWE-1284 CWE-20 CWE-345
Published
Advisory Summary

CVE-2026-33471 is a CRITICAL (CVSS 9.6) nimiq-block has skip block quorum vulnerability (CWE-190: Integer Overflow or Wraparound) affecting Nimiq block libraries in the crates.io ecosystem. The issue involves nimiq-block has skip block quorum bypass via out-of-range bitset indices & u16 truncation. Remediation is available in the latest vendor maintenance releases.

CVE-2026-33471 at a Glance

CVE Identifier CVE-2026-33471
GHSA Identifier GHSA-6973-8887-87ff
Severity CRITICAL
CVSS v3.1 Base Score 9.6
CWE Classification CWE-190: Integer Overflow or Wraparound
Affected Product Nimiq block
Package Ecosystem crates.io
Published Date
Last Updated

Security Impact

CVSS: 9.6

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:H).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required Low (PR:L)
User Interaction None (UI:N)
Scope Changed (S:C)
Confidentiality None (C:N)
Integrity High (I:H)
Availability High (A:H)

How to Fix CVE-2026-33471

To remediate this vulnerability, upgrade all affected Nimiq block dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

nimiq-block fixed: Latest secure release 
Upgrade nimiq-block to Latest secure release
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for nimiq-block

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-33471, inspect your project dependencies for Nimiq block:

inspect dependencies for nimiq-block

Analyze the terminal output to locate any version of Nimiq block in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than the patched release), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-190: Integer Overflow or Wraparound, where the product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. this occurs when an integer value is incremented to a value that is too large to store in the associated representation. when this occurs, the value may become a very small or negative number. In Nimiq block, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### 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](https://github.com/nimiq/core-rs-albatross/pull/3657) is included as part of [v1.3.0](https://github.com/nimiq/core-rs-albatross/releases/tag/v1.3.0). ### Workarounds No known workarounds.

CVE-2026-33471 Affected Nimiq block Versions

1 component(s)
Product / Package Ecosystem Affected Versions Fixed Version
nimiq-block
 crates.io
≤ 0.2.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/nimiq/core-rs-albatross/security/advisories/GHSA-6973-8887-87ff
NVD — CVE-2026-33471 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-33471
Nimiq block Source Repository REPOSITORY
https://github.com/nimiq/core-rs-albatross/pull/3657
Security Fix Commit FIX COMMIT
https://github.com/nimiq/core-rs-albatross/commit/d02059053181ed8ddad6b59a0adfd661ef5cd823
Nimiq block Source Repository REPOSITORY
https://github.com/nimiq/core-rs-albatross
Nimiq block Release RELEASE
https://github.com/nimiq/core-rs-albatross/releases/tag/v1.3.0

Frequently Asked Questions

What is CVE-2026-33471?
CVE-2026-33471 is a security vulnerability in Nimiq block involving nimiq-block has skip block quorum bypass via out-of-range BitSet indices & u16 truncation under CWE-190: Integer Overflow or Wraparound.
Which Nimiq block versions are affected?
Affected versions include releases prior to current release patches across affected packages: nimiq-block.
What version fixes CVE-2026-33471?
Upgrading to current release patches (or the latest patched release for your respective branch) resolves the vulnerability.
Is nimiq-block affected?
Yes, nimiq-block is affected in releases prior to Latest secure release. Upgrade your dependency to Latest secure release or later.
What is the CVSS score of CVE-2026-33471?
CVE-2026-33471 has a CVSS v3.1 base score of 9.6 (CRITICAL) with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:H.
What CWE is associated with CVE-2026-33471?
CVE-2026-33471 is classified under CWE-190: Integer Overflow or Wraparound (The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.).
How can I check crates.io dependencies for CVE-2026-33471?
Run the dependency tree command: 'inspect dependencies for nimiq-block'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-6973-8887-87ff",
  "modified" : "2026-04-27T16:22:04Z",
  "published" : "2026-04-22T19:13:47Z",
  "aliases" : [ "CVE-2026-33471" ],
  "summary" : "nimiq-block has skip block quorum bypass via out-of-range BitSet indices & u16 truncation",
  "details" : "### Impact\n`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.\n\nThis 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.\n\n### Patches\n[The patch for this vulnerability](https://github.com/nimiq/core-rs-albatross/pull/3657) is included as part of [v1.3.0](https://github.com/nimiq/core-rs-albatross/releases/tag/v1.3.0).\n\n### Workarounds\nNo known workarounds.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:H"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "crates.io",
      "name" : "nimiq-block"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "0.2.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/nimiq/core-rs-albatross/security/advisories/GHSA-6973-8887-87ff"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-33471"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nimiq/core-rs-albatross/pull/3657"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nimiq/core-rs-albatross/commit/d02059053181ed8ddad6b59a0adfd661ef5cd823"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/nimiq/core-rs-albatross"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/nimiq/core-rs-albatross/releases/tag/v1.3.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1284", "CWE-190", "CWE-20", "CWE-345" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-22T19:13:47Z",
    "nvd_published_at" : "2026-04-22T20:16:40Z"
  }
}