Source: cret@cert.org
The management portal on ZyXEL PMG5318-B20A devices with firmware 1.00AANC0b5 does not terminate sessions upon a logout action, which allows remote attackers to bypass intended access restrictions by leveraging an unattended workstation.
ZyXEL PMG5318-B20A devices are vulnerable to a critical session management flaw. This allows remote attackers to maintain unauthorized access after a user logs out, potentially leading to complete network compromise and data exfiltration. This vulnerability is easily exploited and poses a significant risk to organizations using these devices.
Step 1: Legitimate Login: A legitimate user logs into the ZyXEL PMG5318-B20A management portal, establishing a valid session.
Step 2: Logout Attempt: The legitimate user attempts to log out of the management portal.
Step 3: Session Persistence: The logout process fails to properly terminate the user's session. The session cookies or tokens remain valid.
Step 4: Attacker Access: An attacker, either physically present or with network access, gains access to the device (e.g., unattended workstation).
Step 5: Session Reuse: The attacker uses the existing session cookies or tokens (obtained through various means, such as sniffing network traffic or accessing the browser's history) to access the management portal without re-authentication.
Step 6: Unauthorized Access: The attacker gains full access to the management portal, allowing them to modify settings, extract sensitive information, or potentially compromise the entire network.
The root cause of CVE-2015-6019 lies in the failure of the ZyXEL PMG5318-B20A's management portal to properly invalidate or terminate user sessions upon logout. Specifically, the logout function does not clear the session cookies or tokens used for authentication. This allows an attacker to reuse the existing session identifiers to bypass authentication and access the management interface. The flaw likely stems from a missing or improperly implemented session management mechanism within the web application code, failing to track and invalidate active sessions correctly. This could be due to a simple oversight in the code or a more complex design flaw in how the application handles user sessions.
While no specific APT groups are directly linked to this CVE, the nature of the vulnerability makes it attractive to various threat actors. The ability to gain persistent access to a network device allows for a wide range of malicious activities. This vulnerability could be leveraged by attackers to establish a foothold for further attacks. CISA KEV status: Not listed.
Monitor network traffic for persistent HTTP/HTTPS sessions to the management portal after a logout is initiated.
Analyze web server logs for suspicious activity, such as continued access to the management portal from the same IP address after a logout.
Examine browser cookies and local storage on potentially compromised devices for session identifiers.
Implement intrusion detection systems (IDS) with rules to detect unauthorized access attempts to the management portal.
Monitor for changes in device configuration or unexpected network behavior that might indicate compromise.
Upgrade the ZyXEL PMG5318-B20A firmware to a patched version that addresses the session management flaw. This is the primary and most effective remediation.
If upgrading is not immediately possible, implement strong password policies for the management portal.
Disable remote access to the management portal if not required.
Segment the network to limit the impact of a compromised device.
Regularly audit device configurations and logs for suspicious activity.
Implement multi-factor authentication (MFA) for the management portal, if available.