# CVE-2026-55440: Microsoft UFO session squatting denial of service in COMMAND_RESULTS handler

Source: https://junglewise.ai/threats/cve-2026-55440-microsoft-ufo-session-squatting-denial-of-service-in-command  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-16. Updated: 2026-07-16  
License: CC BY 4.0 with a link back

CVE-2026-55440 · Severity: medium · CVSS 6.5 · Published 2026-07-16

Microsoft UFO is an open-source framework used for automating tasks across different devices and platforms. A security flaw in how the system handles command results allows an authorized user to 'squat' on or block sessions intended for other users. This can lead to a persistent denial of service where legitimate automation tasks are prevented from running, or the system's memory is exhausted by fake sessions.

Technologies: [Microsoft UFO](https://junglewise.ai/threats/technologies/ufo). Vendors: [Microsoft](https://junglewise.ai/threats/vendors/microsoft).

## Quick answers

**Is CVE-2026-55440 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-55440 being exploited in the wild.

**How severe is CVE-2026-55440?** Medium severity, with a CVSS score of 6.5, published 16 July 2026.

**Which products and versions are affected?** Microsoft UFO < 3.0.7.

**Is there a fix for CVE-2026-55440?** A patch was published on 2026-06-12: Fix committed and version 3.0.7 released. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-55440 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-55440?** Check whether you run Microsoft UFO at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A vulnerability exists in the Microsoft UFO framework due to missing authorization checks in the COMMAND_RESULTS handler. While the TASK message path correctly enforces session ownership, the COMMAND_RESULTS path in `ufo/server/ws/handler.py` calls `get_or_create_session` without providing an `owner_client_id`. Because session IDs are predictable (derived from task names and IDs), an authenticated attacker can pre-create an 'unowned' session. When the legitimate owner later attempts to initiate the task, the system's ownership defense rejects the request because the existing session has no recorded owner. This results in a persistent denial of service (DoS) for specific tasks or general resource exhaustion through the creation of unbounded phantom sessions. The issue is resolved in version 3.0.7 by ensuring the handler only performs lookups and rejects results from non-owners.

## Affected products

- Microsoft UFO < 3.0.7

## Timeline

- 2026-06-12: patched: Fix committed and version 3.0.7 released.
- 2026-07-16: disclosed: Advisory published.

## References

- [https://github.com/microsoft/UFO/commit/cc653bde75337ab60c320e6b7cb61b86ba6ca948](https://github.com/microsoft/UFO/commit/cc653bde75337ab60c320e6b7cb61b86ba6ca948)
- [https://github.com/microsoft/UFO/releases/tag/3.0.7](https://github.com/microsoft/UFO/releases/tag/3.0.7)
- [https://github.com/microsoft/UFO/security/advisories/GHSA-hxjv-fmjf-wmjf](https://github.com/microsoft/UFO/security/advisories/GHSA-hxjv-fmjf-wmjf)

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