GHSA-f3w5-v9xx-rp8p
Signature verification failure in Tendermint
Blast Radius
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Description
The root cause of this security vulnerability is in the Tendermint specification, and this advisory is a duplicate of https://github.com/tendermint/spec/security/advisories/GHSA-jqfc-687g-59pw.
Impact
Tendermint light clients running versions 0.34.0 to 0.34.8 are unable to detect and punish a new kind of attack. We’re calling this a “forward lunatic attack,” or FLA. The severity of this vulnerability is moderate.
Note that an FLA cannot be successfully executed unless there are already ⅓+ Byzantine validators, and therefore outside of Tendermint’s security model; however, it is important to be able to detect and punish these kinds of attacks in order to incentivize correct behavior.
In an FLA, an attacking validator (with ⅓+ voting power) signs commit messages for arbitrary application state associated with a block height that hasn’t been seen yet, hence the name “forward lunatic attacks.” A malicious validator effectively executes a lunatic attack, but signs messages for a target block that is higher than the current block. This can be dangerous: Typically, misbehavior evidence is only created when there are conflicting blocks at the same height, but by targeting a block height that is far “ahead” of the current chain height, it’s possible that the chain will not produce a (conflicting) block at the target height in time to create evidence.
Prior to Tendermint v0.34.9, the light client could accept a bad header from its primary witness, and would not be able to form evidence of this deception, even if all the secondary witnesses were correct. Because the light client is responsible for verifying cross-chain state for IBC, a successful FLA could result in loss of funds. However, it is important to note that FLAs are only possible outside the Tendermint security model.
All FLAs, attempted and successful, leave traces of provable misbehavior on-chain. A faulty header contains signatures from the faulty validator, and even in unpatched versions of Tendermint Core, networks could use social consensus (off-chain action) to recover the network. The patches introduced in Tendermint Core v0.34.9 handle all evidence automatically and on-chain.
Note that this fix also allows for successful automatic reporting of FLAs, even after a chain halt. By adding a time to FetchBlock, light clients effectively have a backup way to determine if a halted chain should have continued, and it will be able to submit evidence as soon as the chain resumes.
Patches
This problem has been patched in Tendermint Core v0.34.9.
Workarounds
There are no workarounds. All users are recommended to upgrade to Tendermint Core v0.34.9 at their earliest possible convenience.
Credits
Thank you to @MaximilianDiez for originally surfacing this issue, and to @cmwaters, @josef-widder, and @milosevic for creating fixes at both the implementation and specification level.
For more information
If you have any questions or comments about this advisory:
- Open an issue in tendermint/tendermint
- Email us at [email protected]
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/tendermint/tendermint | ≥ 0.34.0&&< 0.34.9 | 0.34.9 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/tendermint/tendermint. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update github.com/tendermint/tendermint to 0.34.9 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-f3w5-v9xx-rp8p is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-f3w5-v9xx-rp8p is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-f3w5-v9xx-rp8p. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-f3w5-v9xx-rp8p in your dependencies?
O3 detects GHSA-f3w5-v9xx-rp8p across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.