CVE-2020-15091 is a medium-severity (CVSS 6.5) CWE-347 vulnerability in github.com/tendermint/tendermint. 2 public exploit references exist, so weaponization risk is real. A fix is available for github.com/tendermint/tendermint — see the affected versions and patch details below.
Denial of Service in TenderMint
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2020-15091 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,156 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
github.com/tendermint/tendermintReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
Description
Denial of Service
Tendermint 0.33.0 and above allow block proposers to include signatures for the wrong block. This may happen naturally if you start a network, have it run for some time and restart it without changing the chainID. (It is a misconfiguration to reuse chainIDs.) Correct block proposers will accidentally include signatures for the wrong block if they see these signatures, and then commits won't validate, making all proposed blocks invalid. A malicious validator (even with a minimal amount of stake) can use this vulnerability to completely halt the network.
Tendermint 0.33.6 checks all the signatures are for the block with +2/3 majority before creating a commit.
False Witness
Tendermint 0.33.1 and above are no longer fully verifying commit signatures during block execution - they stop after +2/3. This means proposers can propose blocks that contain valid +2/3 signatures and then the rest of the signatures can be whatever they want. They can claim that all the other validators signed just by including a CommitSig with arbitrary signature data. While this doesn't seem to impact safety of Tendermint per se, it means that Commits may contain a lot of invalid data **.
** This was already true of blocks, since they could include invalid txs filled with garbage, but in that case the application knew that they are invalid and could punish the proposer. But since applications didn't--and don't-- verify commit signatures directly (they trust Tendermint to do that), they won't be able to detect it.
This can impact incentivization logic in the application that depends on the LastCommitInfo sent in BeginBlock, which includes which validators signed. For instance, Gaia incentivizes proposers with a bonus for including more than +2/3 of the signatures. But a proposer can now claim that bonus just by including arbitrary data for the final -1/3 of validators without actually waiting for their signatures. There may be other tricks that can be played because of this.
Tendermint 0.33.6 verifies all the signatures during block execution ***.
*** Please note that the light client does not check nil votes and exits as soon as 2/3+ of the signatures are checked.
Impact
- All nodes
- The network stops due to having a commit with a wrong signature.
Patches
- v0.33.6 andn v0.34.0-dev1.0.20200702134149-480b995a3172
Workarounds
No workarounds.
References
For more information
If you have any questions or comments about this advisory:
- Open an issue in tendermint/tendermint
- Email us at [email protected]
More information can be found here.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/tendermint/tendermint | all versions | 0.33.6go get github.com/tendermint/tendermint@v0.33.6 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
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, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/tendermint/tendermint to 0.33.6 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-15091 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 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2020-15091 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2020-15091. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2020-15091 in your dependencies?
O3 Security finds CVE-2020-15091 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.