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CVE-2026-54403 – Authentication Bypass – Ubiquiti UniFi OS Server (all versions prior to 5.1.19)

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Summary

CVE-2026-54403 is a Path Traversal vulnerability (CWE-22) in Ubiquiti’s UniFi OS Server that allows an unauthenticated, network-accessible attacker to bypass authentication on affected UniFi OS devices and instances. Disclosed on July 2, 2026 and rated CVSS 8.6 (High), the flaw requires no privileges and no user interaction, making it directly exploitable by any attacker with network access to an exposed management interface.

Technical details

  • Root cause: Improper limitation of a pathname to a restricted directory (Path Traversal, CWE-22) within the UniFi OS authentication layer, allowing crafted requests to traverse directory boundaries and reach protected endpoints without valid credentials.
  • Trigger conditions: No authentication required; no user interaction required; no special configuration needed. The vulnerability is exploitable under default deployment conditions with low attack complexity (AC:L).
  • Attack vector: Remote, over the network (AV:N). UniFi OS management interfaces are commonly exposed on TCP ports 443, 8443, or 11443.
  • Impact: Successful exploitation results in complete authentication bypass on the targeted UniFi OS device or instance, granting an unauthenticated attacker access to protected resources. The CVSS vector reflects a Changed Scope (S:C) with High Confidentiality impact (C:H), meaning the compromise can affect components beyond the vulnerable service itself. Integrity and availability are not directly impacted (I:N, A:N).

Affected software

The following Ubiquiti product families running UniFi OS versions prior to 5.1.19 are affected:

  • UniFi OS Server
  • Dream Machines
  • Dream Routers
  • Dream Wall
  • Enterprise Fortress Gateway
  • Express 7
  • Cloud Keys
  • Network Video Recorders (NVR)
  • Enterprise Video Recorders (EVR)
  • Cloud Gateways
  • Network Attached Storage (NAS)
  • Enterprise Firewall Core

Severity

CVSS v3.1 Base Score: 8.6 (High)
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N

Mitigation and recommended actions

  • Immediate action – Patch: Upgrade all affected UniFi OS devices to version 5.1.19 or later, which contains the vendor-provided fix per Ubiquiti Security Advisory Bulletin 066. Updates can be applied through the UniFi OS management console.
  • Network mitigation (if immediate patching is not possible): Restrict network access to UniFi OS management interfaces (TCP 443, 8443, 11443) using firewall rules or network segmentation. Do not expose the management interface directly to the public internet.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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