CVE-2020-5303 (published 2020-04-10T19:15Z)

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.

Severity: MEDIUM
CVSS v2 base score: 4.3 (AV:N/AC:M/Au:N/C:N/I:N/A:P)
CVSS v3 base score: 3.7, LOW (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L)

Weakness information:
cwe_id: CWE-787
cwe_name: Out-of-bounds Write
description: The product writes data past the end, or before the beginning, of the intended buffer.
extended_description: 
            
            
             
			 
         
         

Fix information:
repo_url: https://github.com/tendermint/tendermint
commit_details: repo_url: https://github.com/tendermint/tendermint
author: Anton Kaliaev
author_date: 2020-04-03 15:37:20+04:00
msg: p2p: limit the number of incoming connections

to p2p.max_num_inbound_peers + len(p2p.unconditional_peer_ids)
repository: repo_url: https://github.com/tendermint/tendermint
repo_name: tendermint/tendermint
description: ⟁ Tendermint Core (BFT Consensus) in Go
repo_language: Go
owner: tendermint
file_changes: filename: node.go
change_type: ModificationType.MODIFY
diff: @@ -471,6 +471,11 @@ func createTransport(
 	}
 
 	p2p.MultiplexTransportConnFilters(connFilters...)(transport)
+
+	// Limit the number of incoming connections.
+	max := config.P2P.MaxNumInboundPeers + len(splitAndTrimEmpty(config.P2P.UnconditionalPeerIDs, ",", " "))
+	p2p.MultiplexTransportMaxIncomingConnections(max)(transport)
+
 	return transport, peerFilters
 }
 

programming_language: Go
filename: transport.go
change_type: ModificationType.MODIFY
diff: @@ -7,6 +7,7 @@ import (
 	"time"
 
 	"github.com/pkg/errors"
+	"golang.org/x/net/netutil"
 
 	"github.com/tendermint/tendermint/crypto"
 	"github.com/tendermint/tendermint/p2p/conn"
@@ -122,11 +123,18 @@ func MultiplexTransportResolver(resolver IPResolver) MultiplexTransportOption {
 	return func(mt *MultiplexTransport) { mt.resolver = resolver }
 }
 
+// MultiplexTransportMaxIncomingConnections sets the maximum number of
+// simultaneous connections (incoming). Default: 0 (unlimited)
+func MultiplexTransportMaxIncomingConnections(n int) MultiplexTransportOption {
+	return func(mt *MultiplexTransport) { mt.maxIncomingConnections = n }
+}
+
 // MultiplexTransport accepts and dials tcp connections and upgrades them to
 // multiplexed peers.
 type MultiplexTransport struct {
-	netAddr  NetAddress
-	listener net.Listener
+	netAddr                NetAddress
+	listener               net.Listener
+	maxIncomingConnections int // see MaxIncomingConnections
 
 	acceptc chan accept
 	closec  chan struct{}
@@ -240,6 +248,10 @@ func (mt *MultiplexTransport) Listen(addr NetAddress) error {
 		return err
 	}
 
+	if mt.maxIncomingConnections > 0 {
+		ln = netutil.LimitListener(ln, mt.maxIncomingConnections)
+	}
+
 	mt.netAddr = addr
 	mt.listener = ln
 

programming_language: Go
filename: transport_test.go
change_type: ModificationType.MODIFY
diff: @@ -5,6 +5,7 @@ import (
 	"math/rand"
 	"net"
 	"reflect"
+	"strings"
 	"testing"
 	"time"
 
@@ -134,6 +135,50 @@ func TestTransportMultiplexConnFilterTimeout(t *testing.T) {
 	}
 }
 
+func TestTransportMultiplexMaxIncomingConnections(t *testing.T) {
+	mt := newMultiplexTransport(
+		emptyNodeInfo(),
+		NodeKey{
+			PrivKey: ed25519.GenPrivKey(),
+		},
+	)
+	id := mt.nodeKey.ID()
+
+	MultiplexTransportMaxIncomingConnections(0)(mt)
+
+	addr, err := NewNetAddressString(IDAddressString(id, "127.0.0.1:0"))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if err := mt.Listen(*addr); err != nil {
+		t.Fatal(err)
+	}
+
+	errc := make(chan error)
+
+	go func() {
+		addr := NewNetAddress(id, mt.listener.Addr())
+
+		_, err := addr.Dial()
+		if err != nil {
+			errc <- err
+			return
+		}
+
+		close(errc)
+	}()
+
+	if err := <-errc; err != nil {
+		t.Errorf("connection failed: %v", err)
+	}
+
+	_, err = mt.Accept(peerConfig{})
+	if err == nil || !strings.Contains(err.Error(), "connection reset by peer") {
+		t.Errorf("expected connection reset by peer error, got %v", err)
+	}
+}
+
 func TestTransportMultiplexAcceptMultiple(t *testing.T) {
 	mt := testSetupMultiplexTransport(t)
 	laddr := NewNetAddress(mt.nodeKey.ID(), mt.listener.Addr())

programming_language: Go