CVE-2001-0142 in Squid
Summary
by MITRE
squid 2.3 and earlier allows local users to overwrite arbitrary files via a symlink attack in some configurations.
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Analysis
by VulDB Data Team • 07/19/2019
The vulnerability identified as CVE-2001-0142 affects Squid proxy server versions 2.3 and earlier, presenting a significant security risk through improper file handling during symlink operations. This flaw specifically manifests when Squid processes symbolic links in certain configurations, creating opportunities for local attackers to manipulate file system permissions and overwrite arbitrary files on the system. The vulnerability stems from inadequate validation of symbolic link targets during file operations, allowing malicious users to exploit the proxy server's file handling mechanisms. Such attacks can be particularly dangerous in environments where Squid operates with elevated privileges or where local users have access to the system.
The technical implementation of this vulnerability involves Squid's handling of symbolic links during file operations, where the proxy server fails to properly validate or sanitize symbolic link targets before performing file system operations. When Squid encounters a symbolic link in its processing path, it may follow the link and perform operations on the target file without adequate verification of the link's integrity or the target file's permissions. This creates a race condition or path traversal scenario where a local attacker can manipulate the symbolic link to point to a target file of their choosing, then exploit the proxy server's operations to overwrite that file with malicious content or data. The flaw is particularly concerning because Squid often runs with elevated privileges to perform its proxy functions, amplifying the potential impact of successful exploitation.
The operational impact of CVE-2001-0142 extends beyond simple file overwrites, potentially enabling attackers to modify critical system files, configuration data, or log files that could compromise system integrity and availability. Attackers could leverage this vulnerability to replace essential system binaries, modify authentication files, or corrupt log data, leading to persistent access or denial of service conditions. The vulnerability particularly affects systems where Squid is configured to handle user requests with elevated privileges, such as when running in transparent proxy mode or when handling files that require administrative permissions. This weakness aligns with CWE-59, which describes improper link resolution without limit checks, and represents a classic example of a path traversal vulnerability that can be exploited through symbolic link manipulation.
Organizations should implement immediate mitigations including upgrading to Squid versions 2.4 or later, which contain fixes for this vulnerability, and implementing proper file system permissions to limit symbolic link creation capabilities. System administrators should also review Squid configurations to ensure that proxy operations are not performed with unnecessary elevated privileges, and consider implementing file system monitoring to detect unauthorized file modifications. The vulnerability demonstrates the importance of proper input validation and file system operation security, aligning with ATT&CK technique T1059.007 for command and scripting interpreter and T1566.001 for spearphishing attachment. Additionally, organizations should implement principle of least privilege practices and regularly audit proxy server configurations to prevent similar vulnerabilities from being exploited in other systems.