How severe is CVE-2026-33471?

CVE-2026-33471 has a CVSS 3.x base score of 9.6, rated critical severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability high.

Is CVE-2026-33471 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (12th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-33471?

CVE-2026-33471 affects Nimiq Nimiq Proof-of-stake. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-33471?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

Does CVE-2026-33471 have an EU (EUVD) identifier?

Yes. CVE-2026-33471 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-25054.

When was CVE-2026-33471 published?

CVE-2026-33471 was published on 2026-04-22 and last updated on 2026-06-17.

CVE-2026-33471

CVE-2026-33471 is a critical-severity vulnerability in Nimiq Nimiq Proof-of-stake with a CVSS 3.x base score of 9.6. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-20.

Key facts

Severity: Critical (CVSS 3.x base score 9.6)
EPSS exploit prediction: 0% (12th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-25054
Weakness: CWE-20
Affected product: Nimiq Nimiq Proof-of-stake
Published: 2026-04-22
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2026-33471?: 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.
How severe is CVE-2026-33471?: CVE-2026-33471 has a CVSS 3.x base score of 9.6, rated critical severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is none, integrity high, and availability high.
Is CVE-2026-33471 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (12th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-33471?: CVE-2026-33471 affects Nimiq Nimiq Proof-of-stake. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-33471?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
Does CVE-2026-33471 have an EU (EUVD) identifier?: Yes. CVE-2026-33471 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-25054.
When was CVE-2026-33471 published?: CVE-2026-33471 was published on 2026-04-22 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:nimiq:nimiq_proof-of-stake:*:*:*:*:*:rust:*:*

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