CVE-2000-0976 in X11r6
Summary
by MITRE
Buffer overflow in xlib in XFree 3.3.x possibly allows local users to execute arbitrary commands via a long DISPLAY environment variable or a -display command line parameter.
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Analysis
by VulDB Data Team • 01/26/2025
The vulnerability identified as CVE-2000-0976 represents a critical buffer overflow condition within the XFree 3.3.x xlib library implementation. This flaw exists in the handling of display environment variables and command line parameters, creating a potential pathway for local privilege escalation attacks. The vulnerability stems from insufficient input validation and bounds checking when processing the DISPLAY environment variable or the -display command line option, allowing attackers to overflow memory buffers and potentially execute arbitrary code with elevated privileges.
The technical implementation of this vulnerability involves the xlib library's failure to properly validate the length of input data when processing display identifiers. When a local user provides an excessively long DISPLAY environment variable or uses the -display parameter with extended input, the library attempts to store this data in a fixed-size buffer without adequate bounds checking. This classic buffer overflow scenario occurs because the code does not verify that the input length exceeds the allocated buffer capacity, leading to memory corruption that can be exploited to overwrite adjacent memory locations including return addresses and control data.
From an operational perspective, this vulnerability poses significant risks to systems running XFree 3.3.x implementations, particularly in multi-user environments where local access is possible. Attackers can leverage this weakness to gain elevated privileges and execute malicious code, potentially compromising the entire system. The local nature of the exploit means that any user with access to the system can attempt to trigger the vulnerability, making it particularly dangerous in shared computing environments. The impact extends beyond simple privilege escalation to include potential denial of service conditions and data integrity compromise.
The vulnerability aligns with CWE-121, which specifically addresses stack-based buffer overflow conditions, and represents a common pattern in legacy software implementations where memory management practices were less rigorous. From an ATT&CK framework perspective, this vulnerability maps to privilege escalation techniques and can be categorized under T1068, which covers "Exploitation for Privilege Escalation." The attack vector involves local execution and requires minimal network interaction, making it particularly effective for lateral movement within compromised systems. Organizations should consider implementing input validation controls and memory protection mechanisms as part of their defensive strategies. The recommended mitigation includes upgrading to patched versions of XFree 3.3.x, implementing proper bounds checking in application code, and applying runtime protections such as stack canaries and address space layout randomization to reduce exploit reliability.
This vulnerability demonstrates the importance of proper input validation and memory management in graphical library implementations, highlighting how seemingly minor coding oversights can create significant security risks. The widespread use of XFree 3.3.x in the early 2000s meant that many systems were potentially vulnerable to this class of attack, emphasizing the need for comprehensive security testing of core system libraries and components.