CVE-2026-111762: 
Java vulnerability analysis and mitigation

CVE-2026-111762 is a credential disclosure vulnerability in the A2A Java SDK (the official Java SDK for the Agent2Agent Protocol) where push notification bearer tokens and authentication credentials are logged in cleartext when protobuf deserialization fails. It affects the Maven package org.a2aproject.sdk:a2a-java-sdk-transport-rest in all versions prior to 1.3.0.Final (specifically confirmed in 1.2.0.Final). The vulnerability was published by the National Vulnerability Database on October 20, 2026, and was originally reported and disclosed via GitHub Security Advisory GHSA-x32g-jvvm-4725 on August 28, 2026. It carries a CVSS v4.0 base score of 5.7 (Medium) (Github Advisory, Feedly).

The root cause is classified as CWE-532 (Insertion of Sensitive Information into Log File). In RestHandler.java (line 676/682), the parseRequestBody method catches InvalidProtocolBufferException thrown by JsonFormat.parser().merge() and logs the entire raw JSON request body at SEVERE level. This method is invoked by createTaskPushNotificationConfiguration when clients POST to /v1/tenants/{tenant}/tasks/{taskId}/pushNotificationConfigs, a body that may contain the token (bearer token) and authentication.credentials (OAuth token) fields. Any valid JSON body that fails protobuf deserialization — such as one containing an unknown field under strict parsing or a schema mismatch — triggers the vulnerable log statement, writing secrets to server logs in cleartext. The fix replaces the log call with log.log(Level.SEVERE, "Error parsing JSON request body (length={0})", body != null ? body.length() : 0), logging only the body length (Github Advisory, Patch Commit).

Successful exploitation allows any party with access to server logs or a log aggregation system — including operators, insiders, or attackers who have compromised logging infrastructure — to retrieve push notification bearer tokens and OAuth credentials in cleartext. These stolen credentials can then be used to authenticate to the client's push notification endpoints and send forged task status updates, undermining the integrity of the Agent2Agent communication channel. There is no direct availability or system integrity impact on the server itself, but the credential exposure can enable downstream abuse of client webhook endpoints (Github Advisory, Feedly).

There is no public proof-of-concept exploit and no evidence of in-the-wild exploitation at the time of disclosure. The EPSS score is 0.0, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog. Exploitation requires the attacker to already have access to server logs or a log aggregation system, and push notifications must be enabled on the target deployment — conditions that significantly limit the attack surface (Github Advisory, Feedly).

1. Identify a vulnerable deployment: Confirm the target is running A2A Java SDK versions prior to 1.3.0.Final with push notification capability enabled.
2. Trigger a protobuf deserialization failure: As a client (with low-privilege access to submit push notification configurations), POST a valid JSON body containing an unknown field to /v1/tenants/{tenant}/tasks/{taskId}/pushNotificationConfigs. Example payload:

{
  "url": "https://client.example.com/webhook",
  "token": "secret-bearer-token",
  "authentication": {"scheme": "Bearer", "credentials": "oauth-access-token"},
  "extraField": "value"
}

The extraField causes JsonFormat.parser().merge() to throw InvalidProtocolBufferException. 3. Credential written to logs: The server logs the entire request body at SEVERE level, including secret-bearer-token and oauth-access-token in cleartext. 4. Access server logs: Retrieve the credentials from server log files, a centralized logging system, or a log aggregation platform (e.g., ELK stack, Splunk) where the attacker has read access. 5. Abuse stolen credentials: Use the extracted bearer token or OAuth credentials to authenticate to the client's push notification webhook endpoint and send forged task status updates (Github Advisory).

• Logs: Server log entries containing Error parsing JSON request body: followed by a full JSON body including fields such as token, authentication, or credentials — indicating the pre-patch log format is in use.
• Logs: SEVERE-level log entries from org.a2aproject.sdk.transport.rest.handler.RestHandler or org.a2aproject.sdk.compat03.transport.rest.handler.RestHandler_v0_3 containing raw JSON request bodies.
• Network: Unexpected or unauthorized POST requests to /v1/tenants/{tenant}/tasks/{taskId}/pushNotificationConfigs endpoints with JSON bodies containing unknown fields (e.g., fields not in the protobuf schema), which may be deliberate attempts to trigger the logging behavior.
• Network: Unusual or unauthorized calls to client push notification webhook endpoints (e.g., unexpected task status update notifications) that may indicate forged requests using stolen credentials (Github Advisory).

The primary remediation is to upgrade the A2A Java SDK to version 1.3.0.Final or later, which replaces the vulnerable log statement with one that logs only the body length (v1.3.0.Final Release, Patch Commit). As interim mitigations, restrict access to server logs and log aggregation systems to only authorized personnel, implement log redaction rules to mask sensitive credential fields, and monitor for unauthorized access to logging infrastructure. Rotating any push notification bearer tokens or OAuth credentials that may have been exposed in logs prior to patching is also strongly recommended (Github Advisory).