CVE-2000-0504 in X11r6
Summary
by MITRE
libICE in XFree86 allows remote attackers to cause a denial of service by specifying a large value which is not properly checked by the SKIP_STRING macro.
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Analysis
by VulDB Data Team • 11/03/2024
The vulnerability identified as CVE-2000-0504 resides within the libICE library component of XFree86, a widely used implementation of the X Window System that serves as the foundation for graphical user interfaces across Unix-like operating systems. This flaw specifically affects the SKIP_STRING macro implementation within the Inter-Client Exchange protocol handling mechanisms. The vulnerability manifests when remote attackers send malformed protocol messages containing excessively large values that bypass proper input validation checks. The libICE library functions as a critical communication layer between X client applications and the X server, making it a prime target for exploitation attempts that could compromise the stability and availability of graphical environments.
The technical root cause of this vulnerability stems from inadequate bounds checking within the SKIP_STRING macro, which is responsible for parsing and skipping string data segments in X protocol messages. When processing incoming data streams, the macro fails to validate the size parameter against reasonable limits, allowing attackers to specify values that exceed normal processing capabilities. This unchecked large value manipulation can lead to buffer overflows, memory corruption, or excessive resource consumption within the libICE processing routines. The flaw operates at the protocol parsing layer, where legitimate client-server communications are interpreted and processed, making it particularly dangerous as it can be triggered through normal network-based interactions without requiring authentication or elevated privileges.
The operational impact of this vulnerability extends beyond simple denial of service conditions to potentially compromise entire graphical sessions and system stability. Remote attackers can exploit this weakness to crash X server processes, terminate graphical user interfaces, or force system reboots through sustained exploitation attempts. The vulnerability affects systems running XFree86 versions prior to the security patch, particularly impacting desktop environments, remote desktop implementations, and any applications relying on the Inter-Client Exchange protocol for communication. Given that XFree86 was prevalent across numerous Unix and Linux distributions during this period, the potential attack surface was extensive, affecting both individual workstations and server environments where graphical interfaces were utilized.
Mitigation strategies for this vulnerability require immediate patching of affected XFree86 installations and implementation of network-level protections to restrict access to X server ports. System administrators should prioritize updating libICE components to versions containing proper bounds checking implementations and validate that all X protocol parsing routines properly validate input parameters. Network segmentation and firewall rules can help reduce exposure by limiting direct access to X server ports, while monitoring solutions should track unusual protocol message patterns that might indicate exploitation attempts. This vulnerability aligns with CWE-129, which addresses improper validation of length parameters, and maps to ATT&CK technique T1499.004 for denial of service attacks targeting network services. Organizations should implement comprehensive patch management procedures to ensure all X Window System components receive timely security updates, as this vulnerability demonstrates the critical importance of input validation in network protocol implementations. The flaw underscores the necessity of robust boundary checking mechanisms in protocol parsers and highlights the potential for seemingly minor validation gaps to result in significant system availability impacts.