# CVE-2026-46540: Nimiq light-blockchain: Light blockchain rebranch issue


- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 9 Jun 2026
- **Updated:** 10 Jun 2026
- **Also known as:** GHSA-m3pg-qc2q-mg8c

## What is CVE-2026-46540?

CVE-2026-46540 is a medium-severity vulnerability in nimiq core-rs-albatross, published on 9 Jun 2026. 

### Official description

Nimiq is a Rust implementation of the Nimiq Proof-of-Stake protocol based on the Albatross consensus algorithm. Prior to version 1.4.0, when LightBlockchain::rebranch() adopts a fork chain whose tip is a macro block (checkpoint or election), it only updates self.head but fails to update self.macro_head, self.election_head, self.current_validators, or store the election header in the chain_store. This is in direct contrast with the full Blockchain::rebranch() at blockchain/src/blockchain/push.rs:504-518, which correctly updates all macro/election state when the new head is a macro block. After a rebranch to a macro block, the stale macro_head causes subsequent macro blocks pushed via push() to be verified against the wrong predecessor via verify_macro_successor(&this.macro_head). If the rebranch target was an election block, the stale current_validators causes every subsequent block to fail verify_validators(), completely stalling the light client's chain progression. This issue has been patched in version 1.4.0.

Weakness: CWE-841 (Improper Enforcement of Behavioral Workflow)

## Which versions are affected by CVE-2026-46540?


## How do I fix CVE-2026-46540?

No fix has been published for CVE-2026-46540 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-46540 being exploited?

There is no known exploitation of CVE-2026-46540 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-46540 and fix it if it is affected.

What it is: CVE-2026-46540 is a medium-severity vulnerability in nimiq core-rs-albatross, published on 9 Jun 2026. 
Exploitation: There is no known exploitation of CVE-2026-46540 in the wild and no public exploit code.

Affected product: nimiq core-rs-albatross. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2026-46540/ (Markdown: https://insights.sbomify.com/CVE-2026-46540/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-46540
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-46540
- OSV: https://osv.dev/vulnerability/CVE-2026-46540

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-46540/
Summaries are generated and may contain mistakes; the official description above is the record.