CVE-2001-0738 in sysklogd
Summary
by MITRE
LogLine function in klogd in sysklogd 1.3 in various Linux distributions allows an attacker to cause a denial of service (hang) by causing null bytes to be placed in log messages.
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Analysis
by VulDB Data Team • 12/15/2024
The vulnerability identified as CVE-2001-0738 resides within the LogLine function of klogd, a component of the sysklogd package version 1.3, which was prevalent across multiple Linux distributions during that time period. This flaw represents a classic buffer handling issue that demonstrates the critical importance of proper input validation in system-level logging utilities. The vulnerability specifically manifests when klogd processes log messages that contain null bytes, which are typically used as string terminators in C-based applications. When such null bytes appear within log messages, they can cause the LogLine function to misbehave and enter an infinite loop or hang state, effectively rendering the logging service unavailable to legitimate users and systems.
The technical implementation of this vulnerability stems from the improper handling of null bytes within the LogLine function's string processing logic. In C programming, null bytes are traditionally used to mark the end of strings, and when these characters appear within user-supplied input without proper sanitization, they can disrupt string parsing operations. The LogLine function in klogd was designed to process kernel log messages and forward them to the system log daemon, but it failed to properly handle cases where null bytes were embedded within the log content itself. This failure creates a condition where the function's internal loop or string manipulation routines become trapped, continuously processing the same null-terminated string segments and consuming system resources indefinitely.
From an operational impact perspective, this vulnerability creates a significant denial of service condition that can severely compromise system availability and monitoring capabilities. When an attacker successfully exploits this vulnerability, the klogd service becomes unresponsive and unable to process additional log messages, which means that system administrators lose critical visibility into system events and potential security incidents. This situation is particularly dangerous in enterprise environments where logging is essential for compliance, security monitoring, and system troubleshooting. The hang condition can persist until the system is manually restarted or the klogd process is terminated, potentially leaving the system without proper logging capabilities for extended periods. The vulnerability also demonstrates the broader risk of inadequate input sanitization in system-level utilities, as it can be exploited by any entity capable of sending specially crafted log messages to the system.
The vulnerability aligns with CWE-129, which addresses improper validation of input boundaries, and more specifically relates to CWE-770, which covers allocation of resources without limits or refresh. The attack pattern follows the typical denial of service methodology described in the MITRE ATT&CK framework under the technique T1499, which encompasses various forms of denial of service attacks that target system availability. Organizations affected by this vulnerability should implement immediate mitigations including upgrading to patched versions of sysklogd, implementing input filtering for log messages, and monitoring for unusual log processing behavior. System administrators should also consider implementing additional logging redundancy measures and ensuring that proper access controls are in place to limit who can inject log messages into the system. The incident highlights the critical need for robust input validation in all system-level components, particularly those handling user-supplied or untrusted data, and emphasizes the importance of regular security updates to protect against known vulnerabilities in foundational system utilities.