CVE-2002-0891 in Netscreen ScreenOS
Summary
by MITRE
The web interface (WebUI) of NetScreen ScreenOS before 2.6.1r8, and certain 2.8.x and 3.0.x versions before 3.0.3r1, allows remote attackers to cause a denial of service (crash) via a long user name.
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Analysis
by VulDB Data Team • 10/11/2025
The vulnerability identified as CVE-2002-0891 represents a classic buffer overflow condition affecting the web interface of NetScreen ScreenOS firewall software. This issue specifically targets the authentication handling mechanism within the WebUI component, where the system fails to properly validate the length of user names submitted during the login process. The flaw exists in versions prior to 2.6.1r8 of the 2.6.x series and certain 2.8.x and 3.0.x releases before 3.0.3r1, indicating a widespread vulnerability across multiple release branches of the operating system. The vulnerability is classified under CWE-121 as a stack-based buffer overflow, where insufficient bounds checking allows an attacker to write beyond the allocated memory space for user name storage.
The technical exploitation of this vulnerability occurs when a remote attacker submits an excessively long user name string through the web interface authentication mechanism. This malformed input causes the system to overwrite adjacent memory locations, leading to unpredictable behavior and ultimately resulting in a system crash or complete denial of service. The vulnerability does not require authentication to exploit, making it particularly dangerous as it can be triggered by any remote user attempting to access the web interface. The crash occurs during the processing of the user name field, where the system attempts to store the input without proper length validation, causing the memory corruption that leads to the system instability.
From an operational impact perspective, this vulnerability creates a significant risk for organizations relying on NetScreen firewalls for network security. The denial of service condition effectively renders the web interface inaccessible, preventing legitimate administrators from managing the firewall configuration, monitoring security events, or performing routine maintenance tasks. The impact extends beyond simple service disruption as it can compromise the availability of the entire network security infrastructure, potentially leaving the organization vulnerable to other threats while the firewall is offline. This vulnerability aligns with ATT&CK technique T1499.004 for network denial of service attacks, as it specifically targets the availability of network services through system crashes.
Organizations affected by this vulnerability should prioritize immediate remediation through the application of vendor patches released in versions 2.6.1r8 and 3.0.3r1 respectively. The patch addresses the root cause by implementing proper input validation and length checking for user name fields in the web interface. Additional mitigations include implementing network segmentation to restrict access to the web interface, configuring access control lists to limit who can reach the firewall management interface, and establishing monitoring for unusual authentication attempts that might indicate exploitation attempts. Security teams should also consider implementing intrusion detection systems to monitor for patterns consistent with this specific vulnerability, as the predictable nature of the attack makes it detectable through network traffic analysis. The vulnerability demonstrates the critical importance of input validation in web applications and highlights how seemingly minor flaws in authentication handling can result in complete system compromise through denial of service attacks.