CyberSecBulletin
CVE-2026-34909Exploited in the wildNVD status: Analyzed

Ubiquiti UniFi OS Path Traversal

Published Updated By the CyberSecBulletin desk

CVE-2026-34909 is a critical-severity improper limitation of a pathname to a restricted directory vulnerability in UniFi OS Server from Ubiquiti, with a CVSS 3.1 base score of 10.0 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists version 5.0.8 as the first without the flaw, so updating UniFi OS Server to that release or later removes the exposure. CISA added it to the Known Exploited Vulnerabilities catalogue on June 23, 2026, which means attacks have been observed in the wild.

Patch now

Attackers are already exploiting this vulnerability, according to CISA.

What to do

  1. Update UniFi OS Server to 5.0.8 or a later version.
  2. Update Express to 4.0.14 or a later version.
  3. Update UDM to 5.1.12 or a later version.
  4. CISA's required action: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
  5. Read the advisory on community.ui.com for workarounds and exact fixed builds.
  6. Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.

Affected products and versions

VendorProductAffected versionsFixed in
UbiquitiUniFi OS Serverbefore 5.0.85.0.8
UbiquitiExpressbefore 4.0.144.0.14
UbiquitiUDMbefore 5.1.125.1.12
UbiquitiUDM-Probefore 5.1.125.1.12
UbiquitiUDM-SEbefore 5.1.125.1.12
UbiquitiUDM-Pro-Maxbefore 5.1.125.1.12
UbiquitiUDM-Beastbefore 5.1.115.1.11
UbiquitiEFGbefore 5.1.125.1.12
UbiquitiUDWbefore 5.1.125.1.12
UbiquitiUDRbefore 5.1.125.1.12
UbiquitiUDR7before 5.1.125.1.12
UbiquitiUDR-5Gbefore 5.1.125.1.12
UbiquitiExpress 7before 5.1.125.1.12
UbiquitiUNVRbefore 5.1.125.1.12
UbiquitiUNVR-Probefore 5.1.125.1.12
UbiquitiUNVR-Instantbefore 5.1.125.1.12
UbiquitiUNVR-G2before 5.1.125.1.12
UbiquitiUNVR-G2-Probefore 5.1.125.1.12
UbiquitiENVRbefore 5.1.125.1.12
UbiquitiENVR-Corebefore 5.1.125.1.12
UbiquitiUNAS-2before 5.1.105.1.10
UbiquitiUNAS-4before 5.1.105.1.10
UbiquitiUNAS-Probefore 5.1.105.1.10
UbiquitiUNAS-Pro-4before 5.1.105.1.10
UbiquitiUNAS-Pro-8before 5.1.105.1.10

Version data comes from the organisation that assigned the CVE; 35 further products are omitted here. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
NetworkCan be exploited remotely over a network, including the internet.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
NoneNo account or login is needed.
User interaction
NoneNo action by a victim is required.
Scope
ChangedThe attack can reach beyond the vulnerable component into other systems.
Confidentiality
HighAll data handled by the component can be read.
Integrity
HighData or code can be modified at will.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H. Scored by CNA (hackerone.com).

Official description

A malicious actor with access to the network could exploit a Path Traversal vulnerability found in UniFi OS devices to access files on the underlying system that could be manipulated to access an underlying account.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Improper Limitation of a Pathname to a Restricted Directory

The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.

How developers prevent this class of flaw

  • For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
  • Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
  • Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth.

More Improper Limitation of a Pathname to a Restricted Directory vulnerabilities (CWE-22)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: active, automatable: yes, technical impact: total).
  3. Added to CISA's Known Exploited Vulnerabilities catalogue.
  4. Deadline for US federal agencies to remediate, set by CISA.
  5. Record last changed materially (score, affected products, status or references).

References

Third-party and government advisories

Technical write-ups (may include proof of concept)

Other vulnerabilities in UniFi OS Server

All UniFi OS Server vulnerabilities

Recent Improper Limitation of a Pathname to a Restricted Directory vulnerabilities

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