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The vulnerability resides in the Android synchronous POST request handler of the A2A Java SDK, specifically within the `AndroidA2AHttpClient.createConnection()` and its subsequent synchronous post builder implementation.
Although a prior security fix (GHSA-9rhm) attempted to disable automatic HTTP redirect-following globally across client implementations by setting connection.setInstanceFollowRedirects(false), the synchronous POST builder explicitly overwrites this safe setting with `connection.setInstanceFollowRedirects(followRedirects)` where `followRedirects` defaults to true.
Consequently, when `JSONRPCTransport` and `RestTransport` execute synchronous POST requests using the AuthInterceptor, sensitive authentication credentials configured in allowlisted nonstandard request headers (X-API-Key, API-Key, X-Auth-Token, X-Authentication) are preserved and forwarded across authority boundaries during a cross-authority HTTP 302 redirect.
On Android’s repackaged OkHttp engine, standard `Authorization` headers are stripped during cross-authority redirects, but nonstandard custom authentication headers are retained and leaked to an attacker-controlled or secondary loopback collector endpoint.
An autonomous client needing no human interaction automatically follows the redirect and transmits the full API key or token, leading to unauthorized credential disclosure.
The vulnerability affects version 1.3.0.Final, 1.3.1.Final, and current main, breaking the security model guarantee that automatic redirects are strictly disabled across all client transport mechanisms to prevent accidental secret leakage.
DailyCVE Form:
Platform: A2A Java SDK
Version: v1.3.1.Final
Vulnerability: Credential redirection leakage
Severity: High
date: September 9, 2026
Prediction: Patched fix available
What Undercode Say:
To test and verify the presence of this vulnerability in your local environment, you can execute the Maven test command provided in the regression test suite:
`mvn -pl extras/http-client-android -am -Dtest=AndroidA2AHttpClientRedirectTest -Dsurefire.failIfNoSpecifiedTests=false test`
The underlying code flaw involves the re-assignment of the redirect state in the POST builder:
private boolean followRedirects = true;
public A2AHttpResponse post() throws IOException {
HttpURLConnection connection = createConnection("POST", false);
connection.setInstanceFollowRedirects(followRedirects);
// ...
}
Exploit: (Educational Purposes!)
An attacker sets up a malicious remote A2A agent or compromised server endpoint that responds with an HTTP 302 redirect pointing to an external collector authority when a client performs a synchronous POST request.
When the vulnerable Android client sends a request containing allowlisted authentication headers (X-API-Key, API-Key, X-Auth-Token, X-Authentication), the underlying OkHttp engine automatically follows the redirect while retaining these nonstandard headers.
The confidential API key or token is thus exfiltrated to the attacker’s secondary collector server without requiring any manual user interaction or authorization override.
Protection: from this CVE
To protect against this vulnerability, update the default boolean setting in the synchronous POST builder to disable automatic redirects permanently by default:
- private boolean followRedirects = true; + private boolean followRedirects = false;
Ensuring `followRedirects` is initialized to `false` restores the secure baseline where redirect-following must be explicitly opted into rather than acting as an insecure default, preventing unauthorized credential leakage across domain boundaries.
Impact:
The demonstrated impact is the complete disclosure of confidential API keys or authentication tokens to an unintended external or secondary authority during cross-authority HTTP redirects.
While it does not grant direct code execution or host compromise on its own, it violates core confidentiality boundaries and enables credential harvesting, exposing systems to downstream impersonation risks if the front-door or redirect behavior is compromised in multi-tenant environments.
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Sources:
Reported By: github.com
Extra Source Hub:
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