Source: cve@mitre.org
Guessable magic cookies in X Windows allows remote attackers to execute commands, e.g. through xterm.
Remote command execution is possible on vulnerable X Window systems due to predictable authentication tokens. Attackers can leverage this flaw to gain unauthorized access and execute arbitrary commands, potentially leading to complete system compromise and data exfiltration.
Step 1: Reconnaissance: The attacker identifies a target system running an X server (e.g., via port scanning on port 6000+).
Step 2: Cookie Guessing/Brute-Force: The attacker attempts to guess or brute-force the magic cookie used by the X server. This can be done offline, if the cookie is known, or by attempting connections with different cookies.
Step 3: Connection Attempt: The attacker uses an X client (e.g., xterm) and provides the guessed magic cookie to connect to the X server.
Step 4: Authentication Bypass: If the guessed cookie is correct, the X server authenticates the attacker as a legitimate client.
Step 5: Command Execution: The attacker, now authenticated, can execute commands on the X server, potentially gaining a shell or other privileged access.
The vulnerability stems from the use of guessable 'magic cookies' for authentication in the X Window System. These cookies, used to authorize connections from clients to the X server, are often generated with insufficient entropy, making them predictable. An attacker can guess or brute-force these cookies, allowing them to impersonate a legitimate client and execute commands on the X server. The root cause is the lack of a secure, cryptographically strong method for generating and managing these authentication tokens. Specifically, the random number generation used for the magic cookie is weak, making it susceptible to guessing or brute-force attacks. This is not a buffer overflow or race condition vulnerability, but a weakness in the authentication mechanism itself.
This vulnerability is not typically associated with specific APT groups due to its age and the availability of public exploits. However, any attacker with basic knowledge can exploit it. It is not listed on the CISA KEV.
Monitor network traffic for X Window connections (port 6000+).
Analyze X server logs for suspicious client connections with unusual IP addresses or user agents.
Look for attempts to connect to the X server with a large number of different cookies.
Review system logs for commands executed by unexpected users or processes.
Use intrusion detection systems (IDS) with signatures for known X Window exploitation attempts.
Disable X Window System if not required. Consider using SSH with X forwarding instead.
If X Window is required, use a strong authentication mechanism, such as SSH with X forwarding, or configure the X server to require authentication.
Ensure the X server is only accessible from trusted networks or hosts.
Regularly update and patch the operating system and X Window System software.
Implement a host-based firewall to restrict access to the X server port (6000+).
Use a strong password policy for user accounts.