CVE-2001-1135 in Prestige 642R
Summary
by MITRE
ZyXEL Prestige 642R and 642R-I routers do not filter the routers Telnet and FTP ports on the external WAN interface from inside access, allowing someone on an internal computer to reconfigure the router, if the password is known.
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Analysis
by VulDB Data Team • 07/13/2016
The vulnerability described in CVE-2001-1135 represents a critical network security flaw affecting ZyXEL Prestige 642R and 642R-I router models from the early 2000s. This issue stems from inadequate network segmentation and access control mechanisms within the router's firewall implementation. The vulnerability specifically impacts the router's handling of Telnet and FTP services, which are essential for remote administration and file transfer operations. These services typically operate on well-known ports 23 for Telnet and 21 for FTP, making them prime targets for exploitation when improperly secured.
The technical flaw manifests as a failure in the router's packet filtering capabilities at the network boundary between internal and external interfaces. When a malicious actor gains access to an internal network computer, they can directly access the router's administrative interfaces through the WAN interface without proper authentication barriers. This occurs because the router's firewall rules do not effectively isolate the internal network from external administrative services, creating a path for privilege escalation attacks. The vulnerability is particularly dangerous because it requires only knowledge of the router's administrative password to exploit, making it accessible to both internal and external threat actors who have obtained credentials through social engineering, password cracking, or other means.
The operational impact of this vulnerability extends beyond simple unauthorized access to encompass complete network compromise. An attacker with internal network access can reconfigure the router's settings, potentially redirecting traffic through malicious servers, disabling security features, or creating backdoors for persistent access. This represents a classic case of insufficient network segmentation, where the principle of least privilege is violated, allowing internal users to bypass external security controls. The vulnerability directly relates to CWE-284, which describes improper access control in software systems, and aligns with ATT&CK technique T1078 for valid accounts and T1566 for credential harvesting. Network administrators may face significant challenges in detecting this compromise since the router's configuration changes can be subtle and may not immediately disrupt network services.
Mitigation strategies for this vulnerability involve implementing proper network segmentation through robust firewall rules that strictly enforce access control between internal and external interfaces. The most effective solution requires disabling unnecessary administrative services on the WAN interface or implementing strict access control lists that prevent internal hosts from reaching the router's administrative ports. Network administrators should also enforce strong authentication practices, including multi-factor authentication for router administration, and regularly audit router configurations to detect unauthorized changes. Additionally, the implementation of network monitoring tools that can detect unusual traffic patterns or unauthorized access attempts to router administrative interfaces provides crucial early warning capabilities. Organizations should also consider upgrading to modern router firmware versions that address these fundamental security flaws and implement network access control policies that align with NIST SP 800-53 security controls for access control and system configuration management.