CVE-2021-41173 — go-ethereum

Impact

A vulnerable node is susceptible to crash when processing a maliciously crafted message from a peer, via the snap/1 protocol. The crash can be triggered by sending a malicious snap/1 GetTrieNodes package.

Details

On September 21, 2021, geth-team member Gary Rong (@rjl493456442) found a way to crash the snap request handler . By using this vulnerability, a peer connected on the snap/1 protocol could cause a vulnerable node to crash with a panic.

In the trie.TryGetNode implementation, if the requested path is reached, the associated node will be returned. However the nilness is not checked there.

func (t *Trie) tryGetNode(origNode node, path []byte, pos int) (item []byte, newnode node, resolved int, err error) {
	// If we reached the requested path, return the current node
	if pos >= len(path) {
		// Although we most probably have the original node expanded, encoding
		// that into consensus form can be nasty (needs to cascade down) and
		// time consuming. Instead, just pull the hash up from disk directly.
		var hash hashNode
		if node, ok := origNode.(hashNode); ok {
			hash = node
		} else {
			hash, _ = origNode.cache()
		}

More specifically the origNode can be nil(e.g. the child of fullnode) and system can panic at line hash, _ = origNode.cache().

When investigating this, @holiman tried to find it via fuzzing, which uncovered a second crasher, also related to the snap GetTrieNodes package. If the caller requests a storage trie:

				// Storage slots requested, open the storage trie and retrieve from there
				account, err := snap.Account(common.BytesToHash(pathset[0]))
				loads++ // always account database reads, even for failures
				if account == nil {
					break
				}
				stTrie, err := trie.NewSecure(common.BytesToHash(account.Root), triedb)

The code assumes that snap.Account returns either a non-nil response unless error is also provided. This is however not the case, since snap.Account can return nil, nil.

Patches

--- a/eth/protocols/snap/handler.go
+++ b/eth/protocols/snap/handler.go
@@ -469,7 +469,7 @@ func handleMessage(backend Backend, peer *Peer) error {
 				// Storage slots requested, open the storage trie and retrieve from there
 				account, err := snap.Account(common.BytesToHash(pathset[0]))
 				loads++ // always account database reads, even for failures
-				if err != nil {
+				if err != nil || account == nil {
 					break
 				}
 				stTrie, err := trie.NewSecure(common.BytesToHash(account.Root), triedb)
diff --git a/trie/trie.go b/trie/trie.go
index 7ea7efa835..d0f0d4e2bc 100644
--- a/trie/trie.go
+++ b/trie/trie.go
@@ -174,6 +174,10 @@ func (t *Trie) TryGetNode(path []byte) ([]byte, int, error) {
 }
 
 func (t *Trie) tryGetNode(origNode node, path []byte, pos int) (item []byte, newnode node, resolved int, err error) {
+	// If non-existent path requested, abort
+	if origNode == nil {
+		return nil, nil, 0, nil
+	}
 	// If we reached the requested path, return the current node
 	if pos >= len(path) {
 		// Although we most probably have the original node expanded, encoding
@@ -193,10 +197,6 @@ func (t *Trie) tryGetNode(origNode node, path []byte, pos int) (item []byte, new
 	}
 	// Path still needs to be traversed, descend into children
 	switch n := (origNode).(type) {
-	case nil:
-		// Non-existent path requested, abort
-		return nil, nil, 0, nil
-
 	case valueNode:
 		// Path prematurely ended, abort
 		return nil, nil, 0, nil

The fixes were merged into #23657, with commit f1fd963, and released as part of Geth v1.10.9 on Sept 29, 2021.

Workarounds

Apply the patch above or upgrade to a version which is not vulnerable.

For more information

If you have any questions or comments about this advisory:

• Open an issue in go-ethereum
• Email us at [email protected]