CVE-2026-46538: Microsoft UFO Cross-Device Task Result Injection (CVSS 5.9)

Technical summary

The vulnerability stems from insufficient validation in the constellation client's task completion handling. When a task is dispatched to a target device, the constellation stores a pending Future object indexed by session_id and internally tracks the expected device_id. However, the message completion path (TASK_END handler) only validates the session_id without cross-referencing the originating device against the stored device_id binding. This allows any authenticated peer device to forge a TASK_END message with a matching session_id and have its result data accepted and injected into the victim device's pending Future. The flaw affects CWE-294 (authentication bypass) and CWE-345 (insufficient verification of data authenticity), enabling authenticated cross-device result injection.

Business impact

Organizations relying on Microsoft UFO for orchestrating distributed automation tasks face a risk of task result manipulation. An internal threat actor or compromised peer device could alter task outcomes, leading to incorrect automation decisions, data corruption, or divergent state across the automation fabric. In supply-chain or multi-tenant scenarios, this could enable lateral privilege escalation or data exfiltration by injecting malicious results into privileged automation workflows. The impact is amplified in environments where UFO coordinates critical operations without downstream validation of results.

Affected systems

Microsoft UFO open-source framework version 3.0.1-4-ge2626659 is affected. The vulnerability requires an authenticated peer device within the constellation network, indicating impact is limited to deployments where multiple devices are coordinated through a shared constellation service. Users of earlier or later versions should verify their specific build against the affected commit hash and consult the Microsoft UFO project repository for patched releases.

Exploitability

Exploitation requires an authenticated peer device already connected to the constellation network, making the attack vector network-based but gated by authentication (CVSS PR:L). The attack has medium complexity due to the need to predict or observe the session_id of a target task and synchronize the forged TASK_END message timing. However, once these preconditions are met, injection is reliable and does not require user interaction. The threat is most acute in multi-tenant or loosely-federated constellation deployments where many peers have authentication credentials.

Remediation

The fix requires modification of the TASK_END message handler to validate that the device sending the completion message matches the device_id stored when the task was originally dispatched. This should be enforced as a mandatory check before accepting the result and resolving the pending Future. Additionally, consider implementing message signing or cryptographic binding of task responses to originating devices to prevent session_id reuse attacks. Apply patched versions of Microsoft UFO beyond the affected commit hash; verify the patch in the official Microsoft UFO repository or release notes.

Patch guidance

Check the Microsoft UFO project repository for releases or commits after 3.0.1-4-ge2626659. Update to the latest stable release that includes the device_id validation fix. If you are building from source, pull the latest main branch or a tagged release and rebuild. Test the updated constellation client in a non-production environment to verify that task routing and completion still function correctly across your device fleet before deploying to production.

Detection guidance

Monitor constellation logs for TASK_END messages where the sending device_id does not match the originally assigned target device for a given session_id. Implement alerting on mismatches, as they indicate potential injection attempts. Log all authentication credentials used to connect to the constellation and correlate them with unexpected TASK_END sources. Network-level detection can identify unusual task completion patterns by analyzing task dispatch and completion timelines; tasks completed by devices other than the assignee warrant investigation.

Why prioritize this

While the CVSS score of 5.9 (MEDIUM) reflects the requirement for prior authentication, the attack directly compromises task integrity in automated systems. Organizations running multi-device UFO constellations should prioritize this if peers have different trust levels or if task results feed into security-sensitive decisions. The vulnerability is not in CISA KEV, so it does not carry an active exploitation deadline, but the flaw is straightforward to exploit by insiders or compromised peers and warrants timely remediation to prevent subtle automation failures or lateral movement.

Risk score, explained

The CVSS 3.1 score of 5.9 (MEDIUM) reflects: (AV:N) network reachability via constellation protocol, (AC:H) high complexity due to session_id prediction and timing, (PR:L) requirement for an authenticated peer, (UI:N) no user interaction needed, (S:U) impact confined to the target device's task context, (C:N) no confidentiality breach, (I:H) high integrity impact via result injection, (A:L) low availability impact via potential task failures. The score appropriately penalizes the authentication prerequisite while recognizing the direct integrity threat to automated workflows.

Frequently asked questions