CVE-2000-0455 in Xlock
Summary
by MITRE
Buffer overflow in xlockmore xlock program version 4.16 and earlier allows local users to read sensitive data from memory via a long -mode option.
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Analysis
by VulDB Data Team • 04/21/2026
The vulnerability identified as CVE-2000-0455 represents a classic buffer overflow flaw within the xlockmore xlock program version 4.16 and earlier. This security issue resides in the command-line argument processing mechanism of the xlock utility, which is commonly used as a screen saver and lock program in X Window System environments. The flaw specifically manifests when the program processes the -mode option with an excessively long argument string, creating a condition where memory beyond the allocated buffer boundaries gets accessed or modified.
The technical implementation of this vulnerability stems from improper input validation and buffer management within the xlock program's argument parsing code. When a local user provides a lengthy -mode option argument, the program fails to properly bounds-check the input data before copying it into a fixed-size buffer. This oversight creates a situation where the overflow can overwrite adjacent memory locations, potentially exposing sensitive data that resides in the program's memory space. The vulnerability is classified as a local privilege escalation vector since it requires local system access to exploit, though the impact extends beyond simple privilege elevation to include information disclosure.
From an operational perspective, this buffer overflow vulnerability poses significant risks to systems running vulnerable versions of xlockmore. The exposure of sensitive memory data could include authentication credentials, session tokens, cryptographic keys, or other confidential information stored in the program's memory space. Attackers could leverage this vulnerability to gain unauthorized access to system resources or extract valuable information that could be used for further exploitation. The impact is particularly concerning in multi-user environments where the screen lock program might be running with elevated privileges or access to sensitive user data.
The vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and represents a common pattern in legacy software development where input validation was insufficient or absent. From an adversarial perspective, this issue maps to ATT&CK technique T1068, which involves local privilege escalation, and T1005, covering data from local system storage. The attack surface is relatively narrow since it requires local access and specific knowledge of the xlock program's command-line interface, but the potential for information disclosure makes it a significant concern for system security. Organizations should prioritize updating to patched versions of xlockmore or implementing compensating controls such as restricted command-line access and regular security audits to mitigate this vulnerability.
The remediation strategy involves upgrading to a patched version of xlockmore that properly validates input lengths and implements appropriate buffer management techniques. System administrators should also consider implementing additional security measures such as mandatory access controls, privilege separation, and monitoring for unusual command-line argument patterns that might indicate exploitation attempts. Regular vulnerability assessments and security scanning should be conducted to identify other potential buffer overflow vulnerabilities in legacy system components that may not have received adequate security updates over time.