CVE-2021-41173: DoS via maliciously crafted p2p message

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.

golang 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: golang // 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

diff --- 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 security@ethereum.org