CVE-2020-5303 is a low-severity (CVSS 3.7) CWE-789 vulnerability in github.com/tendermint/tendermint. 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-2020-5303 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 377,636 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/tendermint🐹github.com/tendermint/tendermint🐹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 1
Tendermint 0.33.2 and earlier does not limit the number of P2P connection requests. For each p2p connection, Tendermint allocates XXX bytes. Even though this memory is garbage collected once the connection is terminated (due to duplicate IP or reaching a maximum number of inbound peers), temporary memory spikes can lead to OOM (Out-Of-Memory) exceptions.
Tendermint 0.33.3 (and 0.32.10) limits the total number of P2P incoming connection requests to to p2p.max_num_inbound_peers + len(p2p.unconditional_peer_ids).
Notes:
- Tendermint does not rate limit P2P connection requests per IP (an attacker can saturate all the inbound slots);
- Tendermint does not rate limit HTTP(S) requests. If you expose any RPC endpoints to the public, please make sure to put in place some protection (https://www.nginx.com/blog/rate-limiting-nginx/). We may implement this in the future (https://github.com/tendermint/tendermint/issues/1696).
Denial of Service 2
Tendermint 0.33.2 and earlier does not reclaim activeID of a peer after it's removed in Mempool reactor. This does not happen all the time. It only happens when a connection fails (for any reason) before the Peer is created and added to all reactors. RemovePeer is therefore called before AddPeer, which leads to always growing memory (activeIDs map). The activeIDs map has a maximum size of 65535 and the node will panic if this map reaches the maximum. An attacker can create a lot of connection attempts (exploiting Denial of Service 1), which ultimately will lead to the node panicking.
Tendermint 0.33.3 (and 0.32.10) claims activeID for a peer in InitPeer, which is executed before MConnection is started.
Notes:
InitPeerfunction was added to all reactors to combat a similar issue - https://github.com/tendermint/tendermint/issues/3338;- Denial of Service 2 is independent of Denial of Service 1 and can be executed without it.
Specific Go Packages Affected
github.com/tendermint/tendermint/p2p
Impact
- All full nodes (except for validators who are behind closed networks)
- Node's memory usage increases, then it panics either in the mempool or due to OOM.
Patches
- v0.33.3
- v0.32.10
- v0.31.12
Workarounds
No workarounds.
References
- https://hackerone.com/reports/820317 (not disclosed yet)
- https://github.com/tendermint/tendermint/issues/3338
- https://github.com/tendermint/tendermint/issues/1696
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.
Credits
- fudongbai for discovering and reporting Denial of Service 2
- Ethan Buchman (@ebuchman) for writing a test case for Denial of Service 2 and Tess Rinearson (@tessr) for fixing it
- Anton Kaliaev (@melekes) for fixing Denial of Service 1
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/tendermint/tendermint | ≥ 0.33.0&&< 0.33.3 | 0.33.3go get github.com/tendermint/tendermint@v0.33.3 |
| 🐹Go | github.com/tendermint/tendermint | all versions | 0.31.12go get github.com/tendermint/tendermint@v0.31.12 |
| 🐹Go | github.com/tendermint/tendermint | ≥ 0.32.0&&< 0.32.10 | 0.32.10go get github.com/tendermint/tendermint@v0.32.10 |
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 0.33.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-5303 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-2020-5303 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2020-5303. 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-2020-5303 in your dependencies?
O3 Security finds CVE-2020-5303 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.