Source: cve@mitre.org
SCO OpenServer 5.0.5 through 5.0.7 only supports Xauthority style access control when users log in using scologin, which allows remote attackers to gain unauthorized access to an X session via other X login methods.
SCO OpenServer versions 5.0.5 through 5.0.7 are vulnerable to a critical access control flaw, allowing unauthorized remote access to X sessions. Attackers can bypass the intended authentication mechanism, leading to complete system compromise and data exfiltration.
Step 1: Identify Target: The attacker identifies a SCO OpenServer system running a vulnerable version (5.0.5-5.0.7).
Step 2: Determine Login Method: The attacker determines which login methods are enabled on the target system (e.g., xdm, direct xinit).
Step 3: Establish X Connection: The attacker attempts to connect to the X server using a login method other than scologin. This bypasses the intended authentication.
Step 4: Exploit the Flaw: Because the Xauthority cookie is not properly validated for non-scologin logins, the attacker gains access to the X session.
Step 5: Privilege Escalation (Optional): Once inside the X session, the attacker can potentially escalate privileges further, depending on the system configuration and user permissions.
The vulnerability stems from a flawed implementation of Xauthority access control within SCO OpenServer. The system relies on scologin for proper authentication, which sets up the .Xauthority file correctly. However, other login methods, such as xdm or direct xinit invocations, bypass this mechanism. These alternative methods do not enforce the same access control checks, allowing an attacker to connect to the X server without proper authorization. The root cause is a lack of consistent enforcement of the Xauthority authentication across all login pathways, creating a security gap. The system fails to validate the Xauthority cookie for connections initiated outside of scologin, effectively granting unauthenticated access to the X server.
While no specific APT groups are definitively linked to exploiting this specific CVE, the vulnerability's nature makes it attractive to any attacker seeking remote access. Given the age of the vulnerability and the likely outdated nature of systems running vulnerable versions, it's more likely to be exploited by opportunistic attackers. Not listed on CISA KEV.
Monitor system logs for unusual X server connections, especially from unexpected IP addresses or using non-standard login methods.
Analyze network traffic for X11 protocol communication (port 6000+). Anomalous connections without proper authentication should be investigated.
Review .Xauthority files for unauthorized entries or modifications.
Monitor for suspicious activity within X sessions, such as keylogging or screen capture attempts.
Upgrade to a patched version of SCO OpenServer (if available).
If upgrading is not possible, restrict access to the X server. Disable or restrict the use of login methods other than scologin.
Implement a strong firewall to limit access to the X server ports (6000+).
Regularly audit system logs for suspicious activity.
Consider using a VPN to secure X server connections if remote access is required.
Implement host-based intrusion detection systems (HIDS) to monitor for malicious activity.