CVE-2026-55110 in UniFi OS Server
A malicious actor who lures an authenticated user to a malicious page could exploit a Cross-Origin Resource Sharing (CORS) misconfiguration found in UniFi OS to trigger actions in UniFi OS using that user's session.
Quick answer
Ubiquiti UniFi OS Server and devices should be reviewed and updated if it matches the affected versions. The recommended fix is to apply the vendor-supported patched version or the mitigation steps below, then retest the public website with Fixnx.
Who is affected
Affected versions
- UniFi OS Server and affected UniFi OS device families before 5.1.19
Fixed versions
- UniFi OS 5.1.19 or later for affected device families
How to fix it
CVE-2026-55110 affects UniFi OS Server and devices. The issue means a malicious page may trigger actions using an authenticated user session. Treat this as a priority if the system is reachable by users, tenants, or the network. Update to UniFi OS 5.1.19 or later, or follow the vendor advisory if your branch needs a backport.
- Inventory every UniFi OS Server and devices instance, appliance, container, or package in use.
- Compare installed versions with the affected ranges in the vendor advisory.
- Update to UniFi OS 5.1.19 or later on supported systems.
- If you cannot update today, restrict access to trusted admins and trusted networks only.
- Review logs for unusual access, privilege changes, file access, or failed requests.
- Rotate secrets, tokens, and service accounts if exposure or abuse is suspected.
- Document the change and keep the advisory link with the ticket.
Scan now. Google sign-in is only needed to unlock fix guidance.
Verify the fix
- Confirm the installed version is UniFi OS 5.1.19 or later.
- Confirm exposed admin, API, SFTP, or device access is limited to trusted users.
- Retest the affected workflow after the update or mitigation.
- Review logs again after patching for repeated suspicious activity.
- Run a new Fixnx scan where the affected service is part of the public site.
Related categories
Trusted references
FAQ
What is affected by CVE-2026-55110?
Ubiquiti UniFi OS Server and devices versions listed as affected should be reviewed: UniFi OS Server and affected UniFi OS device families before 5.1.19.
What should I fix first?
Start with internet-facing sites, admin panels, login flows, plugins, themes, modules, packages, and systems that process user-controlled input or sensitive data.
How do I confirm the fix worked?
Apply the patched version or mitigation, clear caches where relevant, retest the affected workflow, and run a new Fixnx scan to verify public website exposure signals.
How are Fixnx security risk categories chosen?
Fixnx keeps one canonical risk page and assigns only broad, relevant categories such as ecosystem, technology area, or vulnerability class.