tendermint-rs's Light Client Verifier allows malicious validators to spoof votes from other validators

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

8.2 · CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N · score source

EPSS

No dated EPSS signal available.

As published by the source; long descriptions are shortened.

Name: ISA-2025-003: Malicious validator can spoof votes from other validators Component: tendermint-rs Criticality: High (Catastrophic Impact; Rare Likelihood per ACMv1.2) 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 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…

Published by the source

9 Apr 2025, 13:01 UTC

Last modified by the source

9 Apr 2025, 13:01 UTC

Source last checked

26 Oct 2026, 15:38 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-6jrf-4jv4-r9mw

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# Patch Next advisory brief: GHSA-6jrf-4jv4-r9mw

Advisory: tendermint-rs's Light Client Verifier allows malicious validators to spoof votes from other validators
IDs: GHSA-6jrf-4jv4-r9mw
Record: https://patchnext.com/advisories/ghsa-6jrf-4jv4-r9mw (revision 1, source checked 26 Oct 2026, 15:38 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: tendermint-light-client-verifier 0.40.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io tendermint-light-client-verifier: affected < 0.40.3; fixed in 0.40.3

## Suggested inspection (read-only)
- crates.io tendermint-light-client-verifier: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on tendermint-light-client-verifier.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-6jrf-4jv4-r9mw (GitHub-reviewed advisory GHSA-6jrf-4jv4-r9mw lists affected ranges: crates.io tendermint-light-client-verifier >=0 <0.40.3)

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