CVE-2002-0004 in Linux
Summary
by MITRE
Heap corruption vulnerability in the "at" program allows local users to execute arbitrary code via a malformed execution time, which causes at to free the same memory twice.
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Analysis
by VulDB Data Team • 11/11/2024
The vulnerability identified as CVE-2002-0004 represents a critical heap corruption issue within the Unix at program, a utility designed to schedule commands for later execution. This flaw exists in the memory management handling of the at daemon, specifically when processing malformed execution time parameters that trigger improper memory deallocation sequences. The at program, which operates as a system service to manage scheduled tasks, becomes susceptible to memory corruption when users provide invalid time specifications that cause the program to attempt freeing the same memory block twice. This double-free condition occurs during the parsing and validation of scheduled execution times, creating a scenario where the heap management structures become corrupted and potentially exploitable by malicious local users. The vulnerability stems from inadequate input validation and memory management practices within the at daemon's code execution path, particularly when handling malformed time specifications that should normally be rejected by the system.
The technical implementation of this vulnerability involves a classic heap corruption pattern where the at program's memory allocation and deallocation functions fail to properly track memory blocks that have already been freed. When a user submits a malformed execution time that triggers the program's internal parsing logic, the at daemon enters a state where it attempts to release memory that has already been deallocated, leading to memory corruption that can be leveraged to execute arbitrary code with the privileges of the at daemon process. This type of vulnerability falls under the CWE-415 category of double free conditions, where the same memory location is freed twice, and is particularly dangerous because it can be exploited to manipulate heap metadata and potentially redirect program execution flow. The vulnerability demonstrates poor memory management practices and insufficient bounds checking in the at program's time parsing routines, creating a path for privilege escalation attacks that can ultimately compromise the entire system.
The operational impact of CVE-2002-0004 extends beyond simple privilege escalation, as local users who can submit scheduled jobs to the at daemon can leverage this vulnerability to gain elevated system privileges and execute malicious code with the permissions of the at daemon process. This presents a significant security risk in multi-user environments where users may have access to the at scheduling functionality but should not possess the ability to execute arbitrary commands with elevated privileges. Attackers can exploit this vulnerability by crafting specific malformed time specifications that cause the at daemon to perform the double-free operation, potentially leading to code execution in the context of the at daemon, which typically runs with system privileges. The vulnerability affects systems where the at program is installed and accessible to local users, making it particularly concerning in shared hosting environments, multi-user systems, and any scenario where the at daemon is actively used for job scheduling. The exploitation of this vulnerability can result in complete system compromise and persistent access for attackers who understand the memory corruption patterns involved.
Mitigation strategies for CVE-2002-0004 require immediate patching of the at program to address the double-free memory corruption issue and implement proper input validation for execution time specifications. System administrators should ensure that all affected systems receive updated versions of the at program that correct the memory management flaws and prevent the double-free condition from occurring during malformed input processing. Additionally, organizations should implement least privilege principles by restricting access to the at scheduling functionality to only authorized users and consider disabling the at daemon if it is not required for system operations. Network segmentation and monitoring should be employed to detect unusual at daemon activity that might indicate exploitation attempts, while regular security audits should verify that no unauthorized modifications have been made to the at program or its associated system files. The vulnerability demonstrates the importance of proper memory management in system services and highlights the need for thorough input validation in all program components that handle user-provided data. Organizations should also consider implementing intrusion detection systems that can identify attempts to exploit heap corruption vulnerabilities through malformed input parameters.