CVE-2026-77539 in UniFi OS Server
Summary
by MITRE • 08/26/2026
A malicious actor with access to the network and high privileges could exploit an Improper Input Validation vulnerability found in UniFi OS Server to execute a Command Injection on the host device.
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Analysis
by VulDB Data Team • 08/26/2026
The identified vulnerability represents a critical security flaw within the UniFi OS Server architecture, specifically categorized as an improper input validation error that facilitates command injection attacks. This type of weakness typically arises when software fails to adequately sanitize or validate user-supplied data before incorporating it into system commands executed by the operating system. In this specific context, the lack of rigorous checks allows a malicious actor who has already established network access and possesses high-level privileges to inject arbitrary shell commands directly onto the host device running UniFi OS. The severity of this issue is compounded by the prerequisite requirement for high privileges, indicating that while remote unauthenticated exploitation may not be feasible, any compromised administrative account or insider threat with elevated permissions can leverage this flaw to gain full control over the underlying infrastructure.
From a technical perspective, command injection vulnerabilities occur when an application passes unsafe user input to a system shell without proper encoding or escaping of special characters. In network management platforms like UniFi OS, such inputs often originate from configuration interfaces, API endpoints, or administrative tools that interact with low-level system processes. When the server fails to distinguish between legitimate data and executable code within these inputs, it inadvertently executes commands intended by the attacker rather than treating them as static text. This mechanism allows for arbitrary command execution on the host operating system, effectively bypassing application-layer security controls and granting the attacker direct access to the kernel-level environment of the network controller or gateway device.
The operational impact of this vulnerability is severe, potentially leading to complete compromise of the managed network infrastructure. An adversary exploiting this flaw could install persistent backdoors, exfiltrate sensitive configuration data including SSID passwords and VPN credentials, pivot into other segments of the internal network by leveraging the privileged position of the UniFi OS host, or disrupt service availability through destructive commands. Furthermore, because UniFi devices often serve as central points for monitoring and controlling enterprise networks, compromising them provides a strategic foothold that can facilitate broader lateral movement attacks against connected endpoints and servers. This aligns with common attack patterns observed in real-world scenarios where initial access is gained through compromised administrative credentials followed by privilege escalation via system-level vulnerabilities.
In terms of industry standard classifications, this vulnerability maps directly to CWE-78: Improper Neutralization of Special Elements used in an OS Command, commonly known as OS Command Injection. Additionally, the exploitation path reflects techniques associated with MITRE ATT&CK T1059: Command and Scripting Interpreter, particularly sub-techniques involving direct shell access or script execution for post-exploitation activities. The requirement for high privileges suggests that this flaw is most dangerous in environments where privilege separation policies are weak or where administrative accounts have been compromised through phishing, credential stuffing, or other initial access vectors.
Mitigation strategies must focus on both immediate remediation and long-term architectural hardening. Organizations should immediately apply vendor-provided patches to update the UniFi OS software to versions that address this input validation flaw. In addition to patching, it is critical to enforce strict network segmentation policies to limit lateral movement in case of a breach. Access controls must be rigorously reviewed to ensure that high-privilege accounts are protected by multi-factor authentication and limited to necessary administrative tasks only. Furthermore, implementing web application firewalls or intrusion detection systems capable of detecting command injection patterns can provide an additional layer of defense against exploitation attempts targeting similar vulnerabilities in other components of the network infrastructure.