A2A Java SDK send client credentials under server-controlled HTTP header name, enabling leakage via redirect

Overview

A2A Java SDK is the official Java SDK for the Agent2Agent (A2A) Protocol. Prior to 1.3.0.Final, a malicious or compromised remote agent can cause the default JDK-based client to forward a configured API key to a third-party server. When a client application configures credentials through CredentialService, AuthInterceptor.intercept in client/transport/spi/src/main/java/org/a2aproject/sdk/client/transport/spi/interceptors/auth/AuthInterceptor.java uses APIKeySecurityScheme.name() from the remote AgentCard directly as the HTTP header name containing the credential, without checking that the declared location is HEADER. JdkA2AHttpClient uses followRedirects(NORMAL), so an agent-controlled cross-origin redirect forwards the custom credential-bearing header even when the standard Authorization header is stripped. The attack requires configured API key credentials for the agent's security scheme and control of the agent's AgentCard and redirect response, but no additional client privileges. This issue is fixed in version 1.3.0.Final.

Affected

• a2a-java < 1.3.0.Final

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.