CVE-2001-0169 in C Library
Summary
by MITRE
When using the LD_PRELOAD environmental variable in SUID or SGID applications, glibc does not verify that preloaded libraries in /etc/ld.so.cache are also SUID/SGID, which could allow a local user to overwrite arbitrary files by loading a library from /lib or /usr/lib.
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Analysis
by VulDB Data Team • 10/10/2024
The vulnerability described in CVE-2001-0169 represents a critical security flaw in the GNU C Library implementation that affects how preloaded libraries are handled in setuid and setgid applications. This issue stems from the improper validation of library loading contexts within the dynamic linking mechanism of glibc, creating a privilege escalation vector that can be exploited by local attackers. The vulnerability specifically targets the interaction between the LD_PRELOAD environment variable and the system's library cache mechanism, exposing a fundamental flaw in access control verification.
The technical root cause of this vulnerability lies in the failure of glibc to perform proper privilege checks when processing preloaded libraries that are referenced in the /etc/ld.so.cache file. When a SUID or SGID application executes with elevated privileges, the system should ensure that any dynamically loaded libraries maintain the same privilege context. However, glibc's implementation does not validate whether preloaded libraries from the cache file are themselves setuid or setgid, allowing attackers to manipulate the library loading process. This oversight creates a scenario where an attacker can substitute a legitimate library with a malicious one that resides in standard library directories such as /lib or /usr/lib, effectively bypassing normal privilege boundaries.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass arbitrary file modification capabilities within the affected system. Local attackers can exploit this weakness by placing malicious libraries in standard library paths, causing setuid/setgid applications to load these compromised libraries instead of the intended ones. The vulnerability is particularly dangerous because it operates at the system level where applications have elevated privileges, potentially allowing attackers to modify system files, create backdoors, or escalate their privileges to root access. This attack vector is especially concerning in multi-user environments where local users may not have direct access to system files but can manipulate library loading through carefully crafted preloaded library paths.
The exploitability of CVE-2001-0169 aligns with several ATT&CK techniques including privilege escalation and persistence mechanisms, as attackers can leverage the vulnerability to maintain access to compromised systems. This vulnerability is categorized under CWE-276 as improper privilege management, specifically focusing on inadequate access control in dynamic library loading. The issue demonstrates a classic security principle violation where the system fails to properly validate the integrity and privilege context of dynamically loaded components. Security practitioners should note that this vulnerability predates modern security hardening techniques and highlights the importance of comprehensive privilege validation in system libraries. Organizations should implement immediate mitigations including restricting the use of LD_PRELOAD in setuid/setgid applications, monitoring for unauthorized library modifications, and ensuring proper file system permissions for critical library directories. The vulnerability also underscores the necessity of regular security audits of system libraries and the importance of maintaining updated system configurations to prevent exploitation of such fundamental implementation flaws.