CVE-2026-77549 Overview
CVE-2026-77549 is a CRLF (Carriage Return Line Feed) injection vulnerability affecting certain devices running Ubiquiti UniFi OS. The flaw allows a network-adjacent attacker to bypass authentication on affected UniFi OS devices or instances under specific conditions. The vulnerability is tracked as CWE-93: Improper Neutralization of CRLF Sequences.
Successful exploitation grants unauthorized access to management interfaces, exposing configuration data, network telemetry, and administrative controls. Ubiquiti published details in the UI Community Security Advisory Bulletin 067.
Critical Impact
Network-based authentication bypass on UniFi OS devices leading to full compromise of confidentiality, integrity, and availability of the management plane.
Affected Products
- Ubiquiti UniFi OS (specific device models and versions listed in vendor advisory)
- UniFi OS instances exposed to network-adjacent attackers
- Refer to the UI Community Security Advisory for exact fixed versions
Discovery Timeline
- 2026-08-26 - CVE-2026-77549 published to NVD
- 2026-08-27 - Last updated in NVD database
Technical Details for CVE-2026-77549
Vulnerability Analysis
The vulnerability stems from improper neutralization of CRLF sequences (\r\n) in input processed by UniFi OS. When an attacker injects unsanitized CRLF characters into request fields, the parser interprets them as protocol delimiters. This enables manipulation of HTTP headers, session tokens, or downstream request routing used for authentication decisions.
Exploitation requires network access and specific preconditions, reflecting the high attack complexity noted in the advisory. Once conditions are met, an unauthenticated attacker can bypass identity verification and reach privileged UniFi OS functionality. The scope change indicates the compromise extends beyond the initial vulnerable component to other resources on the device.
Root Cause
The root cause is missing or incomplete validation of user-supplied input containing carriage return (\r, 0x0D) and line feed (\n, 0x0A) bytes before that input is embedded in protocol messages. UniFi OS handlers use the tainted input to construct or parse HTTP-layer artifacts tied to authentication state, allowing an attacker to inject synthetic headers or split messages.
Attack Vector
The attack is delivered over the network against the UniFi OS management interface. An attacker crafts a request containing CRLF metacharacters embedded in a field that flows into authentication logic. The injected sequences alter the effective request boundaries or header set, causing the device to treat the request as authenticated or to accept attacker-controlled session state.
No verified public exploit code is available at this time. Technical details are documented in the vendor advisory linked above.
Detection Methods for CVE-2026-77549
Indicators of Compromise
- HTTP requests to UniFi OS management endpoints containing raw or URL-encoded CRLF sequences (%0d%0a, \r\n) in headers, cookies, or query parameters.
- Unexpected administrative sessions originating from unusual source IP addresses or subnets not associated with legitimate operators.
- Configuration changes, new admin accounts, or firmware modifications on UniFi OS devices without corresponding change-management records.
Detection Strategies
- Inspect web server and reverse proxy logs for anomalous header structures, duplicated Host or Set-Cookie values, and split responses indicative of CRLF injection.
- Baseline authentication events on UniFi OS and alert on successful logins that lack a preceding credential validation sequence.
- Deploy signature-based intrusion detection rules on management VLANs to flag CRLF metacharacters in HTTP request lines and headers.
Monitoring Recommendations
- Forward UniFi OS syslog and admin audit logs to a centralized SIEM for correlation with network telemetry.
- Monitor egress traffic from UniFi OS devices for connections to unknown external hosts that could indicate post-exploitation activity.
- Alert on privileged API calls executed outside of maintenance windows or from non-approved administrative workstations.
How to Mitigate CVE-2026-77549
Immediate Actions Required
- Apply the firmware updates published by Ubiquiti in Security Advisory Bulletin 067 to all affected UniFi OS devices.
- Remove UniFi OS management interfaces from direct exposure to untrusted networks and the public internet.
- Rotate administrator credentials and API tokens on any device that may have processed suspicious CRLF-bearing requests.
Patch Information
Ubiquiti has released firmware updates addressing the CRLF neutralization defect in UniFi OS. Administrators should consult the vendor advisory for the exact fixed firmware versions per device model and apply updates through the UniFi Network controller or device-level upgrade path.
Workarounds
- Restrict access to UniFi OS management ports using firewall rules that permit only trusted administrative subnets.
- Require VPN or zero-trust network access for all administrative sessions to UniFi OS devices.
- Enable multi-factor authentication on all UniFi OS accounts to reduce the value of any bypassed authentication state.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
