Merge pull request #4701 from joostjager/fix-lsps5-case-replay

Reject case-varied LSPS5 replay signatures

Author: tnull

lightning-liquidity/src/lsps5/validator.rs

@@ -11,7 +11,6 @@
 
 use super::msgs::LSPS5ClientError;
 
-use crate::alloc::string::ToString;
 use crate::lsps0::ser::LSPSDateTime;
 use crate::lsps5::msgs::WebhookNotification;
 use crate::sync::Mutex;
@@ -91,14 +90,17 @@ impl LSPS5Validator {
 	}
 
 	fn check_for_replay_attack(&self, signature: &str) -> Result<(), LSPS5ClientError> {
+		// zbase32 decoding accepts case aliases, so canonicalize the cache key
+		// to match verification semantics without decoding the signature again.
+		let signature = signature.to_ascii_lowercase();
 		let mut signatures = self.recent_signatures.lock().unwrap();
-		if signatures.contains(&signature.to_string()) {
+		if signatures.contains(&signature) {
 			return Err(LSPS5ClientError::ReplayAttack);
 		}
 		if signatures.len() == MAX_RECENT_SIGNATURES {
 			signatures.pop_back();
 		}
-		signatures.push_front(signature.to_string());
+		signatures.push_front(signature);
 		Ok(())
 	}
 }

lightning-liquidity/tests/lsps5_integration_tests.rs

@@ -988,6 +988,16 @@ fn replay_prevention_test() {
 	assert!(replay_result.is_err(), "Immediate replay attack should be detected");
 	assert_eq!(replay_result.unwrap_err(), LSPS5ClientError::ReplayAttack);
 
+	let case_modified_signature = signature.to_ascii_uppercase();
+	assert_ne!(case_modified_signature, signature);
+	let case_modified_replay_result =
+		validator.validate(service_node_id, &timestamp, &case_modified_signature, &body);
+	assert!(
+		case_modified_replay_result.is_err(),
+		"Immediate replay attack should be detected when the signature case changes"
+	);
+	assert_eq!(case_modified_replay_result.unwrap_err(), LSPS5ClientError::ReplayAttack);
+
 	// Fill up the validator's signature cache to push out the original signature.
 	for i in 0..MAX_RECENT_SIGNATURES {
 		// Advance time, allowing for another notification