CVE-2026-46416: Microsoft UFO WebSocket Handler Session Isolation Flaw

Technical summary

CVE-2026-46416 arises from a connection handler pooling defect in Microsoft UFO version 3.0.1-4-ge2626659. The UFOWebSocketHandler class instantiates a single shared object reused across multiple authenticated WebSocket connections. Protocol objects specific to each connection are stored in mutable instance fields on this shared handler. When a new WebSocket connection is established, these instance fields are overwritten with the new connection's protocol context. Subsequently, when message handlers construct and send responses, they reference the shared instance fields rather than the protocol object bound to the originating client's connection. This causes responses destined for the most recently connected client to be routed through the wrong protocol context, allowing that client to receive protocol-level messages from other authenticated users' sessions.

Business impact

For organizations deploying UFO for cross-device or cross-platform automation, this vulnerability compromises session isolation and introduces an information disclosure risk. An authenticated attacker within the environment could capture automation responses, logs, or other protocol-level data belonging to other users. In scenarios where UFO orchestrates sensitive operations—configuration deployment, credential handling, or sensitive query results—the exposure could be significant. The attacker requires valid authentication, limiting the threat to insider scenarios or situations where credentials have been compromised, but the damage potential is elevated given the operational nature of automation frameworks.

Affected systems

Microsoft UFO versions including 3.0.1-4-ge2626659 are affected. The vulnerability requires authenticated access to a UFO WebSocket endpoint, so exposure is limited to environments where UFO services are deployed and reachable by authenticated users. Open-source deployments and any commercial or internal uses of UFO with that commit or similar versions warrant assessment. Organizations should verify their deployed version against the official Microsoft UFO repository and advisory.

Exploitability

The vulnerability requires valid authentication credentials and network access to a UFO WebSocket service (CVSS vector: AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L). An attacker cannot exploit this remotely without credentials. However, once authenticated, exploitation is straightforward: the attacker simply establishes a WebSocket connection and receives responses from concurrent users' sessions without additional interaction. The lack of user interaction required and low attack complexity make this feasible in multi-user environments or where credentials are shared or compromised.

Remediation

Apply patches from Microsoft UFO's official repository. Patch versions addressing this issue will include a refactored handler design that either creates per-connection handler instances or correctly isolates protocol context to prevent field overwrites. Organizations should also audit their UFO deployments to identify concurrent authenticated users and assess whether sensitive data has been exchanged. Implement network-level access controls to limit UFO WebSocket access to trusted internal networks and authenticated users.

Patch guidance

Monitor the Microsoft UFO project repository for patch releases following the 2026-05-27 publication date. Patches will likely increment the version beyond 3.0.1-4-ge2626659 and should be verified against the official Microsoft UFO advisory before deployment. Apply patches to all instances of UFO in your environment, paying particular attention to production systems handling sensitive automation workflows. Verify patch application by checking the version string and confirming the underlying code uses per-connection handler instances or proper protocol isolation.

Detection guidance

Detect exploitation by monitoring UFO WebSocket logs for patterns of multiple concurrent authenticated connections where response messages are logged against mismatched client identifiers or session tokens. Look for cases where a client receives protocol responses that do not align with its issued requests. Enable detailed logging of all WebSocket connection lifecycle events (connect, disconnect, message send/receive) and correlate client IDs with message origination. Network-level detection is harder given the use of encrypted WebSocket (WSS); focus on application-level logging and anomaly detection around session association.

Why prioritize this

This vulnerability merits moderate priority for organizations using UFO in multi-user or multi-tenant environments. The CVSS score of 6.3 (Medium) reflects that exploitation requires authentication and has bounded impact. However, the confidentiality and integrity implications (data from other users' sessions) justify prompt patching in security-sensitive deployments. Organizations where UFO handles automation of privileged operations, configuration management, or sensitive queries should treat this as higher priority. Isolated or single-user UFO deployments face lower risk.

Risk score, explained

The CVSS 3.1 score of 6.3 (Medium severity) factors in the requirement for prior authentication (PR:L), network-accessible attack vector (AV:N), low attack complexity (AC:L), and impacts to confidentiality, integrity, and availability (C:L/I:L/A:L) within the affected user's security context (S:U). The score appropriately reflects that an authenticated insider or account-compromise scenario is required, but once that barrier is crossed, exploitation is trivial and the data exposure is real. No user interaction is needed, and the complexity of mounting the attack is minimal.

Frequently asked questions