How severe is CVE-2020-15091?

CVE-2020-15091 has a CVSS score of 6.5/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2020-15091?

CVE-2020-15091 affects the following packages: github.com/tendermint/tendermint (Go). Ecosystems affected: Go.

How do I fix CVE-2020-15091?

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.

How do I detect CVE-2020-15091 in my Go dependencies?

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.

How do I mitigate CVE-2020-15091 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2020-15091 actively exploited in the wild?

Yes. There are 2 known exploit references for CVE-2020-15091, including 2 in-the-wild exploitations observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2020-15091?

CVE-2020-15091 has an EPSS (Exploit Prediction Scoring System) score of 0.9%, placing it in the 60th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2020-15091?

CVE-2020-15091 is classified as CWE-347 (CWE-347). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2020-15091 published, and has it been updated?

CVE-2020-15091 was published on July 2, 2020 and was last updated on October 20, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹

🐹 Go

Not in CISA KEV

MEDIUM severity

CVE-2020-15091 — tendermint

MEDIUMFix: tendermint/tendermint@480b995

CVE-2020-15091 is a medium-severity (CVSS 6.5) CWE-347 vulnerability in github.com/tendermint/tendermint. 2 public exploit or proof-of-concept references are indexed, 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

Also known asGHSA-6jqj-f58p-mrw3GO-2021-0090

Published

Jul 2, 2020

Updated

Oct 20, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

2 known

Exploitation data as of Nov 8, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

0.9%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs60th percentile — riskier than 60% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected

🐹github.com/tendermint/tendermint

Real-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

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

https://github.com/tendermint/tendermint/issues/4926

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

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/tendermint/tendermint`	all versions	0.33.6`go get github.com/tendermint/tendermint@v0.33.6`

Affected Products

1 product · 1 configurations

Application

tenderminttendermint

≥ 0.33.0 && < 0.33.6

range

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

TenderMint from version 0.33.0 and before version 0.33.6 allows block pr…

github.comNVDJul 2020

Report on github.com

github.comNVDJul 2020

Detection & mitigation playbook

Open-source dependency

Detect
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
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Frequently Asked Questions

### 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](https://docs.tendermint.com/master/tendermint-core/using-tendermint.html) 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 a