Description

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.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "10.0",
  "pubDate": "2026-08-26T11:16:38.930Z",
  "pubdate": "2026-08-26T11:16:38.930Z",
  "executiveSummary": "This vulnerability involves an Improper Neutralization of CRLF Sequences within UniFi OS, which manifests as a critical security flaw allowing for the potential circumvention of authentication mechanisms.\nThe vulnerability allows a network-adjacent malicious actor to manipulate HTTP responses or headers by injecting carriage return (CR) and line feed (LF) characters into input vectors that are insufficiently sanitized by the device's web service component.\nThe primary risk implication is unauthorized access to the UniFi OS management interface, which could lead to full administrative compromise of the device.\nSuccessful exploitation requires the attacker to have network-level access to the target device, enabling them to intercept or influence traffic processing to facilitate an authentication bypass.\nThe lack of proper header validation within the application layer permits the injection of malicious sequences that alter the intended behavior of the web server’s interaction with the client, effectively bypassing security controls meant to protect authentication flows.",
  "technicalDetails": "The vulnerability stems from the improper handling of user-supplied data that is subsequently reflected in HTTP headers without adequate neutralization of CRLF sequences. When the UniFi OS web component processes these inputs, it fails to encode or reject CR (%0D) and LF (%0A) characters, allowing an attacker to inject arbitrary header fields or terminate the current response prematurely to initiate a new one.\nThe attack flow begins when an unauthenticated network actor crafts a malicious request containing CRLF characters. By injecting these sequences, an attacker can manipulate the HTTP response stream. Specifically, if the application inserts user input into a header (e.g., Set-Cookie or Location), the attacker can terminate the initial header block and inject a secondary response or modify the session context.\nIn the context of an authentication bypass, the attacker may exploit this to force the application into an inconsistent state where security checks are skipped or redirected. By injecting headers such as 'Set-Cookie' or manipulating redirection logic, the attacker can influence the session state to mirror that of an already authenticated user, or bypass the logic that validates the integrity of the session token.\nThe underlying issue is a failure in the input sanitization layer of the web server stack. Because the web application does not implement strict validation or header splitting protection, the server interprets the injected CRLF as the legitimate end of the header section. Subsequent data provided by the attacker is then treated as part of the HTTP message body or, worse, as an entirely new HTTP response, potentially leading to HTTP Response Splitting or Request Smuggling scenarios.\nThe exploitation surface is network-exposed, requiring only connectivity to the management port of the UniFi OS device. There are no implicit privilege requirements for the attacker initially, as the objective is to elevate privileges or bypass the authentication gate entirely. Once the crafted payload is processed, the server may provide an authenticated session cookie or redirect the attacker to an internal administrative endpoint that normally requires elevated privileges, effectively granting the attacker full administrative control over the UniFi OS instance."
}