# CVE-2026-34068: nimiq-transaction: UpdateValidator transactions allows voting key change without proof-of-knowledge

> An attacker could potentially forge quorum justifications by bypassing proof-of-knowledge checks in validator updates, compromising consensus integrity.

- **Severity:** Medium 6.8 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 22 Apr 2026
- **Updated:** 23 Apr 2026
- **Also known as:** GHSA-pf4j-pf3w-95f9

## What is CVE-2026-34068?

CVE-2026-34068 is a medium-severity vulnerability in nimiq-transaction, published on 22 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

nimiq-transaction provides the transaction primitive to be used in Nimiq's Rust implementation. Prior to version 1.3.0, the staking contract accepts `UpdateValidator` transactions that set `new_voting_key=Some(...)` while omitting `new_proof_of_knowledge`. this skips the proof-of-knowledge requirement that is needed to prevent BLS rogue-key attacks when public keys are aggregated. Because tendermint macro block justification verification aggregates validator voting keys and verifies a single aggregated BLS signature against that aggregate public key, a rogue-key voting key in the validator set can allow an attacker to forge a quorum-looking justification while only producing a single signature. While the impact is critical, the exploitability is low: The voting keys are fixed for the epoch, so the attacker would need to know the next epoch validator set (chosen through VRF), which is unlikely. The patch for this vulnerability is included as part of v1.3.0. No known workarounds are available.

Weakness: CWE-347 (Improper Verification of Cryptographic Signature)

## Which versions are affected by CVE-2026-34068?

2 open source packages ship an affected version, including nimiq-transaction. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `nimiq-transaction` | crates.io | All versions to 0.2.0 | None |
| `nimiq-transaction` | crates.io | All versions to 0.2.0 | None |

Products: Nimiq Nimiq Proof-of-Stake.

## How do I fix CVE-2026-34068?

No fix has been published for CVE-2026-34068 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-34068 being exploited?

There is no known exploitation of CVE-2026-34068 in the wild and no public exploit code.

## Other vulnerabilities in nimiq-transaction

- [CVE-2026-33471](https://insights.sbomify.com/CVE-2026-33471/): nimiq-block has skip block quorum bypass via out-of-range BitSet indices & u16 truncation (critical 9.6)
- [CVE-2026-40093](https://insights.sbomify.com/CVE-2026-40093/): nimiq-blockchain is missing a wall-clock upper bound on block timestamps (high 8.1)
- [CVE-2026-34063](https://insights.sbomify.com/CVE-2026-34063/): network-libp2p: Peer can crash the node by opening discovery protocol substream twice (high 7.5)
- [CVE-2026-34065](https://insights.sbomify.com/CVE-2026-34065/): nimiq-primitives: Node crash due to missing interlink validation in election macro block proposals (high 7.5)
- [CVE-2026-32605](https://insights.sbomify.com/CVE-2026-32605/): Nimiq: Remote crash via off-by-one signer bounds check in proposal buffer (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-34068 and fix it if it is affected.

What it is: CVE-2026-34068 is a medium-severity vulnerability in nimiq-transaction, published on 22 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-34068 in the wild and no public exploit code.

Affected packages and fixed versions:
- nimiq-transaction (crates.io): affected all versions up to 0.2.0; no fix listed
- nimiq-transaction (crates.io): affected all versions up to 0.2.0; no fix listed

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-34068/ (Markdown: https://insights.sbomify.com/CVE-2026-34068/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-34068
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-34068
- OSV: https://osv.dev/vulnerability/CVE-2026-34068

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-34068/
Summaries are generated and may contain mistakes; the official description above is the record.