CVE-2026-77550

Executive Summary

CVE-2026-77550 is a critical, unauthenticated authentication bypass vulnerability affecting devices running UniFi OS. The flaw resides in an Improper Neutralization of CRLF Sequences (CWE-93) issue that enables a remote, network-accessible attacker to bypass authentication mechanisms entirely. With a CVSS score of 10.0 (Critical), the vulnerability allows complete compromise of confidentiality, integrity, and availability of the affected UniFi OS devices or instances, with no user interaction or privileges required.

Given that no patch is currently available (Patch Confidence: 0/4), all existing UniFi OS deployments are considered exposed. This vulnerability is particularly concerning for enterprise environments that rely on UniFi networking equipment (access points, switches, gateways, and cloud controllers) as part of their network infrastructure, as a successful exploit could grant an attacker administrative control over network devices, enabling traffic interception, configuration tampering, and lateral movement.

Technical Analysis

The vulnerability is classified as CWE-93: Improper Neutralization of CRLF Sequences. This weakness class involves the failure to sanitize or encode Carriage Return (0x0D) and Line Feed (0x0A) characters in user-supplied input before incorporating them into HTTP headers, logs, or other protocol-level constructs.

Vulnerability Mechanism: In the context of UniFi OS, the CRLF injection flaw allows an attacker to manipulate HTTP response headers or internal data structures by injecting \r\n sequences into fields that are subsequently processed by the authentication mechanism. Because the application does not neutralize these sequences, an attacker can forge or alter authentication-related data—such as session tokens, redirect targets, or header-based trust indicators—during the request/response cycle.

Attack Surface: The attack surface is the network-facing HTTP/HTTPS management interface of UniFi OS. This includes:

• UniFi OS Consoles (e.g., Cloud Key, Dream Machine series)
• Self-hosted UniFi Network Controller instances running UniFi OS
• UniFi cloud-hosted management interfaces

Authentication Bypass Mechanism: By injecting CRLF sequences into a request targeting the authentication flow, an attacker can:

1. Terminate the current header line prematurely
2. Inject additional HTTP headers that influence the server-side authentication decision
3. Manipulate redirect headers to bypass credential validation
4. In instances where logs are implicated, inject forged log entries to confuse auditing mechanisms, though primary impact is authentication bypass

Note: The NVD description provides no specific function names, parameter names, or exact request paths. The technical detail above is derived from the vulnerability class (CWE-93) and its known exploitation patterns in web-based authentication gateways. Insufficient technical detail is available to identify the precise code-level flaw.

CVSS Rationale: The scoring reflects:

• AV:N — Remotely exploitable over the network
• AC:L — No special conditions or race conditions required
• PR:N — No privileges needed to exploit
• UI:N — No user interaction required
• S:C — Security scope change: compromise extends beyond the vulnerable component
• C:H/I:H/A:H — Complete loss of confidentiality, integrity, and availability

Exploitation Scenarios

No public PoC, exploit code, or Nuclei template exists for this CVE at the time of writing. The attack chain below is inferred from the vulnerability class (CRLF injection leading to authentication bypass) according to standard exploitation techniques.

Step 1 — Reconnaissance/Target Identification: The attacker scans the internet for publicly accessible UniFi OS management interfaces. Default ports (TCP 443 for HTTPS, 8443 for web management) and distinctive TLS certificates identifying Ubiquiti devices are used as fingerprints. Shodan queries such as "UniFi", "Ubiquiti", or http.title:"UniFi" can quickly identify vulnerable targets.

Step 2 — Triggering the CRLF Flaw: The attacker crafts a specially formatted HTTP request to the authentication endpoint. The payload includes CRLF (%0d%0a) sequences injected into a field—such as a redirect URL, username parameter, or cookie value—that the server processes during the authentication flow. The server fails to neutralize these sequences, allowing the attacker to inject additional headers or terminate the response early to influence subsequent authentication logic.

Step 3 — Payload Execution (Vulnerability-Class Level): At the class level, the attack proceeds as follows:

• The injected CRLF characters allow the attacker to add a response header like Location: pointing to an attacker-controlled URL, or to forge a session-related header.
• Alternatively, the attacker may manipulate the server's internal state so that the authentication check returns a "success" condition without valid credentials.
• The result is that the server believes the attacker has authenticated, and it responds with a valid session token or grants access to the administrative interface.

Step 4 — Post-Exploitation Impact: Once authenticated as an administrator, the attacker gains full control over the UniFi OS device. Post-exploitation activities include:

• Exfiltrating network configuration data and client credentials stored on the device
• Modifying firewall rules, VLAN configurations, and Wi-Fi settings
• Deploying custom firmware or backdoors for persistent access
• Using the compromised device as a pivot point for lateral movement into the internal network
• Intercepting or redirecting network traffic traversing the device

Confidence Note: This attack chain is a reasonable inference from the CRLF authentication bypass class. Specific implementation details (exact parameters, endpoints) are unavailable from public data; organizations should treat this as a realistic but possibly incomplete model of the actual exploit path.

Impact Assessment

Business Impact: Catastrophic. A successful exploit grants complete administrative control over the affected UniFi device. For enterprise deployments, this means:

• Network Infrastructure Compromise: Access points, switches, and gateways become attacker-controlled, allowing traffic sniffing, DNS tampering, and man-in-the-middle attacks.
• Configuration Integrity Loss: Adversaries can modify VPN settings, routing tables, and ACLs, potentially creating persistent access paths or causing denial of service.
• Data Breach: UniFi consoles often store site configuration data, client information, and in some cases, RADIUS user databases.
• Regulatory Consequences: If the compromised device passes or stores regulated data (e.g., PCI-DSS in retail environments), breach notification obligations and compliance penalties may apply.

Blast Radius: CVSS reveals a Scope Change (S:C), meaning compromise of the vulnerable device extends to integrated systems. The blast radius goes beyond the single device: the UniFi OS controller often manages multiple network segments, and credentials harvested or network pivots established can expose internal applications and data.

Affected Systems: All devices and instances running UniFi OS. Since no version range is specified, assume all current releases are vulnerable until a patch is issued.

Exploitability Considerations: The attack is trivially exploitable (AC:L, PR:N, UI:N), requires no special user action, and can be launched by any network-reachable actor. Public exploit development is likely imminent given the criticality and the known vulnerability class mechanics.

Detection Guidance

The below detection rules target the observable network and host artifacts typical of CRLF injection against web authentication endpoints. Because no field-proven exploit signature exists, these rules should be considered heuristic and require tuning to your environment.

Sigma Rule

title: UniFi OS CRLF Injection - Authentication Bypass Attempt
id: 6b3f1a2e-8c4d-4f6e-9a0b-1c2d3e4f5a6b
status: experimental
description: Detects HTTP requests with encoded CRLF sequences targeting UniFi OS authentication endpoints, potentially indicating an authentication bypass attempt.
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2026-77550
author: Valters IT Security Team
date: 2026/02/10
tags:
    - attack.initial-access
    - attack.t1190
logsource:
    category: webserver
    product: nginx
detection:
    selection_crlf:
        cs-method:
            - 'GET'
            - 'POST'
        cs-uri-query|contains:
            - '%0d'
            - '%0a'
            - '%0D'
            - '%0A'
            - '\r\n'
    selection_auth_paths:
        cs-uri-query|contains:
            - 'auth'
            - 'login'
            - 'session'
    condition: selection_crlf and selection_auth_paths
falsepositives:
    - Legitimate use of encoded characters in unusual URI parameters
    - Web application firewalls re-encoding requests
level: high

YARA Rule

rule UniFi_OS_CRLF_Injection_Auth_Bypass {
    meta:
        author = "Valters IT Security Team"
        description = "Detects HTTP payloads containing CRLF injection patterns targeting UniFi OS"
        reference = "CVE-2026-77550"
        date = "2026-02-10"
    strings:
        $crlf1 = "%0d%0a" ascii
        $crlf2 = "%0D%0A" ascii
        $crlf3 = "\\r\\n" ascii
        $unifi = "unifi" ascii nocase
        $auth = "auth" ascii nocase
        $login = "login" ascii nocase
        $cookie = "cookie" ascii nocase
        $session = "session" ascii nocase
    condition:
        (
            uint16(0) == 0x0d0a or
            $crlf1 or $crlf2 or $crlf3
        ) and
        any of ($unifi, $auth, $login, $cookie, $session)
}

Suricata IDS Rule

alert http any any -> any any (
    msg:"CVE-2026-77550 - UniFi OS CRLF Injection Authentication Bypass Attempt";
    flow:to_server,established;
    content:"unifi"; nocase; http_uri;
    pcre:"/(?:%0d%0a|%0D%0A|%250d%250a|%0a%0d)/i";
    http_uri;
    classtype:attempted-admin;
    reference:cve,2026-77550;
    sid:20267750;
    rev:1;
    metadata:created_at 2026_02_10, updated_at 2026_02_10;
)

Note: The PCRE pattern looks for double-encoded sequences too, as WAF bypass attempts may try to defeat naive filters.

Elastic Detection

sequence by source.ip with maxspan=1m
  [ network where dns.question.name : "*unifi*" ]?
  [ http where http.request.method in ("GET","POST") and
    (http.request.body_bytes like "*%0d%0a*" or
     http.request.uri like "*%0d%0a*" or
     http.request.uri like "*%0D%0A*" or
     http.request.uri like "*%0a%0d*") and
    (http.request.uri like "*auth*" or
     http.request.uri like "*login*" or
     http.request.uri like "*session*" or
     http.request.body_bytes like "*auth*")
  ]

Note: Adjust index patterns and field names to match your Elastic deployment's HTTP data model (e.g., http.request.body_bytes vs http.request.body.content).

Splunk SPL Query

index=web sourcetype=access_combined
  (uri_query="*%0d%0a*" OR uri_query="*%0D%0A*" OR uri_query="*%0a%0d*" OR uri_query="*%0A%0D*")
  AND (uri_path="*auth*" OR uri_path="*login*" OR uri_path="*session*" OR uri_path="*api*")
  | stats count by src_ip, uri_path, uri_query, http_user_agent
  | where count > 3

Adding a threshold requirement reduces false positives from occasional legitimate encoding usage.

Wazuh OSSEC Rule

<group name="web,authentication,failed,">
    <rule id="202677" level="15">
        <if_sid>31100</if_sid>
        <match>unifi</match>
        <regex>%0d%0a|%0D%0A|%0a%0d|%0A%0D</regex>
        <description>CVE-2026-77550: Possible CRLF injection attempting authentication bypass on UniFi OS.</description>
        <group>attack.initial_access,t1190,</group>
        <mitre>
            <id>T1190</id>
        </mitre>
    </rule>
</group>

If rule ID 31100 (generic web access) is not in your Wazuh setup, replace if_sid with a suitable parent rule ID from your config.

Mitigation & Patch Guidance

Patch Status: No patch is available. Vendor has not released a fix (Patch Confidence: 0/4), and no affected version list has been published. Treat all UniFi OS versions as vulnerable.

1) Immediate Mitigations (Network-Level):

• Restrict access: If remote management is not strictly required, disable internet access to the UniFi OS management interface entirely. Place it behind a VPN or allowlist source IP addresses.
• Apply access control lists (ACLs) on external firewalls to block untrusted sources from reaching ports 443, 8443, and any custom management ports used by UniFi OS.
• Deploy a Web Application Firewall (WAF) with rules to block requests containing CRLF-encoded sequences (%0d%0a, %0D%0A, \r\n) in HTTP headers, URI paths, or POST bodies.

2) Patch/Upgrade Steps:

• Monitor the Ubiquiti security advisory page and the CVE entry continuously for any patch releases.
• When a patch is issued, apply it to all UniFi OS instances immediately, starting with internet-facing devices.
• Consider the urgency: this vulnerability has a CVSS of 10.0 and is remotely exploitable. If you cannot isolate the device, schedule an emergency maintenance window to disable remote management until a fix is available.

3) Long-Term Hardening:

• Enable Multi-Factor Authentication (MFA) on all admin accounts. Even if an attacker bypasses the primary authentication, MFA significantly raises the bar for account takeover.
• Audit administrative accounts: Remove unused accounts, enforce strong password policies, and rotate credentials periodically.
• Network segmentation: Place UniFi management interfaces on an isolated management VLAN with strict egress/ingress controls.
• Monitor for VPN or remote access logs to detect suspicious authentication events, even if the bypass is silent.
• Implement logging and alerting: Forward UniFi OS syslog to your SIEM to retain forensic evidence.
• Adopt least-privilege: Designate site administrators with the minimum permissions needed for their roles.

References

1. NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2026-77550 — Official CVE record with current NVD description and CVSS vector.
2. MITRE ATT&CK: https://attack.mitre.org/techniques/T1190/ — Technique reference for Exploit Public-Facing Application initial access.
3. CWE-93 Reference: https://cwe.mitre.org/data/definitions/93.html — Improper Neutralization of CRLF Sequences, the root weakness class.
4. Shodan Search: https://www.shodan.io/search?query=unifi+os — Search query used to identify internet-exposed UniFi OS devices for environment exposure assessment.
5. Ubiquiti Security Advisories: https://community.ui.com/releases — Monitor for vendor patch announcements and updated security advisories.

Threat Actor Activity: No known threat actor campaigns have been publicly attributed to this CVE, no exploit-in-the-wild evidence exists (CISA KEV: NO), and no public PoC has been released. However, given the criticality score of 10.0 and the known history of Ubiquiti devices being targeted by IoT botnets (e.g., Mirai variants) and APT groups for network pivoting, we assess a high likelihood of imminent weaponization. Security teams should treat this as an active, one-day-style (0-day) risk profile.