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GHSA-hvrp-rf83-w775
No affected components available
Summary
In affected versions, the default request handlers installed by the experimental tasks feature (server.experimental.enable_tasks()) did not check which session created a task before acting on it. On a server with more than one connected client, any client could observe, read results from, and cancel tasks belonging to other clients.
Am I affected?
Only if the developer's application server calls server.experimental.enable_tasks(). If grep -r enable_tasks over their codebase finds nothing, the application is not affected.
Details
When tasks support is enabled on the low-level server, default handlers are registered for tasks/list, tasks/get, tasks/result, and tasks/cancel. These handlers operated on the task identifier alone and kept no record of the session that created each task. Because tasks/list returned every task in the store, a connected client did not need to know any identifiers in advance: it could enumerate all tasks, read any task's status and result via tasks/get and tasks/result, retrieve queued task messages — such as elicitation requests intended for the task's creator, which are removed from the queue on delivery, so the intended recipient never receives them — and cancel any task via tasks/cancel.
Impact
Servers that call server.experimental.enable_tasks() and serve multiple clients are affected: one client can read other clients' task results and elicitation payloads, consume messages meant for them, and cancel their tasks. The feature is experimental and opt-in, so servers that never enable it are unaffected. Servers that registered their own task handlers instead of the defaults are affected only if those handlers have the same omission.
Mitigation
Upgrade to version 1.27.2 or later, in which task IDs generated by run_task() embed an opaque per-session marker and the default handlers restrict each session to its own tasks: requests for another session's task receive "task not found", and tasks/list returns only the requesting session's tasks. Tasks created with explicitly chosen IDs or written directly through a TaskStore remain reachable by ID but are not listed. Alternatively, leave the experimental tasks feature disabled, or register task handlers that validate session ownership.
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker needs basic access or low-level privileges. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a high impact on the confidentiality of the information. There is a low impact on the integrity of the data. There is a low impact on the availability of the system.
Exploitation activity has been observed. Apply available patches or mitigations urgently.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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