A2A Java SDK has a fail-open default task authorization

Draft text for GHSA-qw47-mcm5-934w. The body below drops into the GitHub advisory description field; the metadata block maps to the form fields. Set the patched version at release; publish when the fix ships._

• Ecosystem: Maven
• Affected package: org.a2aproject.sdk:a2a-java-sdk-server-common (task store / authorization)
• Affected versions: <= 1.2.0.Final (and 1.2.1.Final-SNAPSHOT on main prior to the fix)
• Patched version: (the release that carries the fix, e.g. 1.2.1.Final)
• CWE: CWE-1188 (Insecure Default Initialization), CWE-862 (Missing Authorization)
• Severity: High
• CVSS v3.1: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N (7.5, High)

Details

The default task store performs no authorization on task reads. InMemoryTaskStore's no-arg constructor sets authorizationProvider = null, and InMemoryTaskStore.get(String taskId) is a bare map lookup with no authorization check regardless of provider:

public InMemoryTaskStore() {
    this.authorizationProvider = null;   // default wiring
}

@Override
public @Nullable Task get(String taskId) {
    return tasks.get(taskId);            // no owner / caller check
}

Authorization is enforced only when the application both supplies a TaskAuthorizationProvider and routes requests through AuthorizationRequestHandlerDecorator (via CDI), which checks ownership before delegating. A server that uses the default store, or wires DefaultRequestHandler.builder().build() manually, or integrates through a non-CDI stack (e.g. Spring), never reaches that check. The safe posture is therefore opt-in and the shipped default is the unsafe one. A caller can read a task created by another caller simply by knowing or guessing its id.

Summary

With the SDK's default configuration, task reads are not authorized: any caller can retrieve a task (including its status, context, message history, and artifacts) created by another caller, by supplying the task id.

PoC

Using only the real production classes wired the default way (no mocks):

1. Construct the default store: InMemoryTaskStore store = new InMemoryTaskStore(); (no-arg constructor, so no authorization provider).
2. As one caller, save a task: store.save(victimTask, false); with id victim-task-42.
3. As a second, unrelated caller with no auth context, read it back: store.get("victim-task-42").

The second caller receives the first caller's task in full, with no authorization check:

unauthenticated get(victim-task-42) returned task owned by nobody-checked: victim-task-42 / ctx=victim-ctx

Verified on main (commit 72d220c, JDK 21) and reproduces unchanged on 1.2.0.Final.

Impact

Task data crosses caller boundaries with no authorization. In any multi-caller deployment built on the default wiring, one caller can enumerate and read another caller's tasks, including task status, context id, the message history, and any artifacts the task carries, which for agent workloads is frequently sensitive input and generated content. Because the insecure behaviour is the default rather than a misconfiguration, it is easy to ship unintentionally, and in the default/reference deployment the transport endpoints are served without authentication enforced, so the read is reachable by an unauthenticated caller (PR:N). CVSS is scored against the default configuration as shipped.

Remediation

Fail closed by default: deny task reads when no authorization provider is configured, rather than treating a missing provider as allow-all, and apply the authorization check in the store's get path (not only in list and the CDI decorator) so it holds regardless of how the handler is wired. If the current permissive default is retained for single-user/testing scenarios, emit a prominent startup warning when the server comes up with no authorization provider so it cannot be shipped by accident.

Workarounds

Until a fixed release, configure a TaskAuthorizationProvider and ensure requests are routed through the authorization decorator (CDI wiring), rather than relying on the default no-arg store or a manually built handler.

References

• CWE-1188: Insecure Default Initialization of Resource: https://cwe.mitre.org/data/definitions/1188.html
• CWE-862: Missing Authorization: https://cwe.mitre.org/data/definitions/862.html