A2A Java SDK: Push notification credentials logged in cleartext on protobuf parse failure

Impact

Push notification bearer tokens and authentication credentials submitted by clients are written to server log files in cleartext. Any operator, log aggregation system, or attacker with log access can read these secrets and use them to authenticate to the client's push notification endpoints, potentially sending forged task status updates.

Where

transport/rest/src/main/java/org/a2aproject/sdk/transport/rest/handler/RestHandler.java:676 in parseRequestBody

What

The parseRequestBody method logs the entire JSON request body at SEVERE level when JsonFormat.parser().merge() throws InvalidProtocolBufferException. This method is called from createTaskPushNotificationConfiguration (line 377), where the body contains client-supplied push notification bearer tokens (field token) and authentication credentials (field authentication.credentials). These secrets are written to server log files in full.

Exploit Scenario

A client creates a push notification configuration by POSTing to /v1/tenants/{tenant}/tasks/{taskId}/pushNotificationConfigs with a body containing {"url": "https://client.example.com/webhook", "token": "secret-bearer-token", "authentication": {"scheme": "Bearer", "credentials": "oauth-access-token"}, "extraField": "value"}. The extra field causes JsonFormat.parser().merge() to throw InvalidProtocolBufferException. The entire body including secret-bearer-token and oauth-access-token is logged at SEVERE level. An attacker with log access retrieves the cleartext credentials.

Preconditions

• Attacker must have access to server log files (centralized logging, log aggregation, shared infrastructure, or insider access)
• Push notification capability must be enabled
• A request body must fail protobuf deserialization while being valid JSON (unknown fields with strict parsing, schema mismatches)

Fix

Do not log the raw request body. Log only a sanitized summary — body length and content type, not content. Replace the log call with something like: log.log(Level.SEVERE, "Error parsing JSON request body (length={0})", body != null ? body.length() : 0).

Verification

3/3 lens verifiers confirmed.