# GHSA-6jrf-4jv4-r9mw: tendermint-rs's Light Client Verifier allows malicious validators to spoof votes from other validators

> Malicious validators can spoof votes to bypass light client verification, allowing acceptance of fraudulent blocks in tendermint-rs.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 9 Apr 2025

## What is GHSA-6jrf-4jv4-r9mw?

GHSA-6jrf-4jv4-r9mw is an authentication bypass vulnerability in tendermint-light-client-verifier, published on 9 Apr 2025. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Name: ISA-2025-003: Malicious validator can spoof votes from other validators 
Component: tendermint-rs
Criticality: High (Catastrophic Impact; Rare Likelihood per [ACMv1.2](https://github.com/interchainio/security/blob/main/resources/CLASSIFICATION_MATRIX.md))
Affected versions: <= v0.40.2
Affected users: Everyone

### Description

tendermint-rs contains a critical vulnerability in its light client implementation due to insecure handling of corrupted validator sets. Because it doesn't check that the validator address is correctly derived from the validator's public key when counting votes, it is possible to spoof votes from other validators. The result is being able to construct the malicious block and cheat the light client. The light client will accept such a block, seemingly signed by 2/3+ majority.

### Patches

The new tendermint-rs release [v0.40.3](https://github.com/informalsystems/tendermint-rs/releases/tag/v0.40.3) fixes this issue.

Unreleased code in the main branch is patched as well.

### Workarounds

There are no known workarounds for this issue.

### Timeline

* March 12, 2025, 13:41pm PST: Issue reported
* March 12, 2025, 03:00am PST: Core team completes validation of issue

This issue was reported by Felix Wilhelm from [Asymmetric Research](https://www.asymmetric.re/).

## Which versions are affected by GHSA-6jrf-4jv4-r9mw?

2 open source packages ship an affected version, including tendermint-light-client-verifier.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `tendermint-light-client-verifier` | crates.io | All versions | 0.40.3 |
| `tendermint-light-client-verifier` | crates.io | All versions | 0.40.3 |

## How do I fix GHSA-6jrf-4jv4-r9mw?

Upgrade tendermint-light-client-verifier to 0.40.3 or later.

## Is GHSA-6jrf-4jv4-r9mw being exploited?

There is no known exploitation of GHSA-6jrf-4jv4-r9mw in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for GHSA-6jrf-4jv4-r9mw and fix it if it is affected.

What it is: GHSA-6jrf-4jv4-r9mw is an authentication bypass vulnerability in tendermint-light-client-verifier, published on 9 Apr 2025. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of GHSA-6jrf-4jv4-r9mw in the wild and no public exploit code.

Affected packages and fixed versions:
- tendermint-light-client-verifier (crates.io): affected all versions; fixed in 0.40.3
- tendermint-light-client-verifier (crates.io): affected all versions; fixed in 0.40.3

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/GHSA-6jrf-4jv4-r9mw/ (Markdown: https://insights.sbomify.com/GHSA-6jrf-4jv4-r9mw/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/GHSA-6jrf-4jv4-r9mw

---
From sbomify Insights: https://insights.sbomify.com/GHSA-6jrf-4jv4-r9mw/
Summaries are generated and may contain mistakes; the official description above is the record.