A2A Java SDK EUVD-2026-111072

Requires an authenticated, network-reachable client able to submit task operations (PR:L) to an A2A Java server built on DefaultRequestHandler/TaskManager at version 1.2.0.Final or earlier. The specific trigger confirmed by the patch is concurrent, overlapping state-changing requests for the SAME task id - two simultaneous cancels, or a cancel racing a concurrent completion - exploiting the unserialized check-then-act in the cancel/saveTaskEvent path. Limiting factors: exploitation needs valid authenticated access and precise timing to win the race window against a single shared task, and impact is confined to task-state integrity/availability (no confidentiality exposure per VC:N); single-threaded or non-concurrent request patterns will not trigger it.

This is a genuinely moderate issue, not an urgent one, and the signals are largely consistent. The CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:L/UI:N) with a base score of 5.3 indicates a network-reachable flaw requiring low privileges and no user interaction, but with only low integrity and low availability impact (VI:L/VA:L) and explicitly no confidentiality impact (VC:N). The vuln.today decision label is 'this_month' - a routine patch priority, not act_now or emergency. It is NOT on CISA KEV, and no EPSS probability was supplied, so exploitation likelihood cannot be quantified from the input; EPSS absence is a data gap, not a low-risk signal. No SSVC exploitation/automatable/technical-impact decision points were provided beyond the single vuln.today label. The source evidence confirms the mechanism: a check-then-act race in the task state machine (TaskManager.saveTaskEvent and the onCancelTask path) where two concurrent cancels, or a cancel racing a completion, can both observe the pre-transition state and both act, corrupting task state. One notable inconsistency: the 'Information Disclosure' tag conflicts with the authoritative CVSS vector, which sets VC:N (no confidentiality impact) - the fix addresses state-machine integrity under concurrency, not data exposure, so the disclosure framing appears unsupported by the vector and the patch. Overall: a real but low-to-moderate integrity/availability defect in a niche SDK, worth patching on a normal cycle rather than an emergency basis.

An authenticated client of an A2A Java server submits two overlapping requests against the same task - for example two concurrent cancel requests, or a cancel timed against an in-flight completion event. Because the cancel path reads the task, checks it is not terminal, and only then enqueues the state-changing event without serialization, both requests can act on the stale pre-transition state and drive the task into an inconsistent terminal state. No public exploit identified at time of analysis; triggering it reliably requires precise timing of concurrent requests to the same task id.