CVE-2026-77550 in Cloud Gateways
Summary
by MITRE • 08/26/2026
A malicious actor with access to the network could exploit an Improper Neutralization of CRLF Sequences vulnerability found in certain devices running UniFi OS to bypass authentication to such UniFi OS devices or instances.
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Analysis
by VulDB Data Team • 08/26/2026
The discovery of a Critical severity vulnerability within UniFi OS, specifically categorized as Improper Neutralization of Carriage Return and Line Feed sequences (CRLF), represents a significant security regression for Ubiquiti's network management infrastructure. This flaw allows an attacker who has gained access to the local network segment hosting the affected device or software instance to bypass authentication mechanisms entirely. The vulnerability stems from inadequate input validation in how the application processes HTTP headers, particularly those related to session cookies and redirection logic. When a malicious actor crafts specific requests containing embedded CRLF characters within header fields, they can manipulate the server's response behavior. This manipulation often leads to the injection of new HTTP headers or the alteration of existing ones, which can effectively reset authentication states or trick the application into accepting forged credentials. The impact is severe because it grants unauthorized administrative access without requiring valid user credentials, potentially allowing full control over network configurations, device settings, and sensitive data stored within the UniFi ecosystem.
From a technical perspective, this vulnerability aligns with CWE-13, which defines Improper Neutralization of CRLF Sequences in HTTP Headers. The root cause lies in the failure to sanitize or encode special characters before they are processed by the web server's backend logic. In many modern web applications, including those built on frameworks used by Ubiquiti, headers such as Set-Cookie or Location are susceptible to injection if not properly validated. By injecting a carriage return and line feed sequence, an attacker can terminate the current header field prematurely and inject additional fields. For instance, this technique can be used to overwrite session cookies with values controlled by the attacker, thereby impersonating an authenticated user. Alternatively, it may allow for HTTP response splitting attacks where the server's output is manipulated to serve malicious content or redirect users to phishing sites. The exploitation does not require complex payload construction beyond standard CRLF characters and a basic understanding of HTTP protocol mechanics, making it accessible to attackers with moderate skill levels who have network-level access.
The operational impact of this vulnerability extends far beyond simple unauthorized access. UniFi OS serves as the central nervous system for many enterprise and small-to-medium business networks, managing everything from Wi-Fi access points and switches to security gateways and cameras. An attacker gaining administrative control can reconfigure firewall rules to allow external traffic into previously protected internal segments, effectively creating a backdoor into the entire corporate network. They can also disable logging mechanisms to cover their tracks or install persistent malware on connected devices for long-term espionage. Furthermore, because UniFi OS often handles sensitive user data and authentication tokens across multiple services, compromising it could lead to broader credential stuffing attacks if those credentials are reused elsewhere in the organization's IT infrastructure. The ability to bypass authentication means that traditional perimeter defenses like firewalls and intrusion detection systems may fail to detect or prevent this specific attack vector unless they inspect HTTP header content for CRLF anomalies specifically targeting web application logic rather than just network-level threats.
Mitigation strategies must address both immediate remediation and long-term architectural improvements. The primary defense is the deployment of vendor-provided software updates that patch the input validation flaws in UniFi OS components responsible for handling HTTP headers. Administrators should prioritize updating all affected devices to the latest stable release as soon as it becomes available from Ubiquiti's official support channels. In environments where immediate patching is not feasible, network segmentation plays a crucial role; restricting access to UniFi management interfaces to only trusted IP addresses or VLANs can significantly reduce the attack surface for local network-based exploits. Additionally, implementing Web Application Firewalls (WAF) with rules specifically designed to detect and block CRLF injection attempts in HTTP headers provides an additional layer of defense. Security teams should also enforce strict session management policies, such as short-lived tokens and secure cookie attributes like HttpOnly and Secure, which can mitigate the impact if a header manipulation attack partially succeeds by preventing client-side script access to sensitive cookies.
This incident highlights the importance of adhering to robust security development lifecycle practices, particularly in input validation and output encoding. The vulnerability maps directly to MITRE ATT&CK technique T1190, Exploit Public-Facing Application, as it leverages a flaw in an application exposed to network traffic for initial access. It also relates to T1534, Internal Spearphishing, if the attacker uses the compromised UniFi instance to facilitate further social engineering within the organization by spoofing internal communications or credentials. To prevent future occurrences of CWE-13 and similar injection flaws, developers must implement strict allow-lists for input characters rather than relying on block-lists which can be easily bypassed using encoding variations. Automated static application security testing (SAST) tools should be integrated into the CI/CD pipeline to detect improper neutralization patterns before code reaches production environments. Regular penetration testing focused on HTTP header manipulation and session management weaknesses is also recommended to identify such vulnerabilities proactively. By combining timely patching, network segmentation, WAF deployment, and rigorous development practices, organizations can effectively mitigate the risks associated with this critical authentication bypass vulnerability in UniFi OS infrastructure.