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.

Affected: Go: github.com/tendermint/tendermint

### 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…