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The A2A Java SDK vulnerability, tracked under CVE-2026-111762, involves a critical information disclosure weakness in the HTTP REST transport layer.
Specifically, the system fails to safely sanitize inbound JSON request bodies when an error occurs during Protocol Buffer deserialization within RestHandler.java.
When clients interact with push notification configuration endpoints, they transmit sensitive data including push bearer tokens and third-party authentication credentials.
If a request body contains malformed structures, unexpected JSON properties, or schema mismatches, `JsonFormat.parser().merge()` triggers an InvalidProtocolBufferException.
Rather than dropping or redacting the payload, the exception handling routine logs the full, unredacted raw request body at the `SEVERE` log level.
Because log files are routinely aggregated, stored in central search systems, or accessed by monitoring services, sensitive tokens are permanently written to disk in plain text.
Any internal user, system administrator, log management platform, or malicious insider with standard log read privileges can extract these plain text secrets.
With these compromised bearer tokens and OAuth credentials, an attacker can impersonate legitimate endpoints and issue forged task status updates.
The root cause lies in printing the raw request payload instead of recording sanitized operational metadata such as HTTP status codes or body length.
Remediation requires removing raw body logging entirely and sanitizing error responses across all REST transport handlers.
DailyCVE Form:
Platform: A2A Java SDK
Version: Before 1.3.0.Final
Vulnerability: Information Exposure Log
Severity: Medium
date: Oct 20 2026
Prediction: Patch Already Released
What Undercode Say:
Analytics
An analysis of the source code reveals that error handling in `RestHandler.java` prioritizes verbose diagnostic context over secret confidentiality. When processing requests via createTaskPushNotificationConfiguration, incoming JSON payloads are merged directly into Protobuf message instances. The presence of extra fields triggers strict parser validation exceptions, driving execution directly into a catch block that logs the entire payload string at Level.SEVERE. Automated static code analysis tools often flag raw payload logging in error handlers as high-risk CWE-532 patterns. Systems integrated with SIEM or centralized logging infrastructure automatically store these secrets in indexed storage, multiplying the attack surface. Upgrading to version 1.3.0.Final or higher replaces raw string output with length metrics, completely mitigating cleartext exposure.
Exploit: (Educational Purposes!)
Triggering raw JSON logging exposure with an extra unexpected field
curl -X POST "https://vulnerable-a2a-server.com/v1/tenants/demo-tenant/tasks/task-101/pushNotificationConfigs" \
-H "Content-Type: application/json" \
-d '{
"url": "https://client.example.com/webhook",
"token": "secret-bearer-token-12345",
"authentication": {
"scheme": "Bearer",
"credentials": "oauth-access-token-998877"
},
"extraField": "invalid_trigger"
}'
// Vulnerable snippet in RestHandler.java
private void parseRequestBody(String body, Message.Builder builder) {
try {
JsonFormat.parser().merge(body, builder);
} catch (InvalidProtocolBufferException e) {
// Vulnerable: Raw request body containing sensitive tokens is written directly to logs
log.log(Level.SEVERE, "Failed to parse JSON request body: " + body, e);
}
}
Protection:
// Remediated code pattern
private void parseRequestBody(String body, Message.Builder builder) {
try {
JsonFormat.parser().merge(body, builder);
} catch (InvalidProtocolBufferException e) {
// Secure: Log only payload metadata instead of cleartext contents
log.log(Level.SEVERE, "Error parsing JSON request body (length={0})", body != null ? body.length() : 0);
}
}
Impact:
Cleartext leakage of push notification bearer tokens and OAuth credentials into application server logs. Unauthorized actors with log access can reuse credentials to authenticate against client webhooks and submit forged task status updates.
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Sources:
Reported By: github.com
Extra Source Hub:
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