CVE-2001-0170 in C Library
Summary
by MITRE
glibc 2.1.9x and earlier does not properly clear the RESOLV_HOST_CONF, HOSTALIASES, or RES_OPTIONS environmental variables when executing setuid/setgid programs, which could allow local users to read arbitrary files.
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Analysis
by VulDB Data Team • 10/10/2024
The vulnerability described in CVE-2001-0170 represents a critical security flaw in the GNU C Library version 2.1.9x and earlier implementations. This issue specifically affects how the system handles environmental variables during the execution of setuid and setgid programs, creating a potential privilege escalation vector that could be exploited by local attackers. The flaw resides in the improper clearing of critical environmental variables including RESOLV_HOST_CONF, HOSTALIASES, and RES_OPTIONS, which are typically used for DNS resolution and host name resolution configuration.
The technical implementation of this vulnerability stems from the glibc library's failure to sanitize environmental variables before transitioning from a privileged to an unprivileged execution context. When a setuid or setgid program executes, the system should clear potentially dangerous environment variables that could influence program behavior or provide unauthorized access to system resources. However, in affected versions of glibc, these variables retain their values, allowing local users to manipulate the program's behavior through carefully crafted environment variable settings. The RESOLV_HOST_CONF variable typically points to host alias configuration files, HOSTALIASES contains host name aliases, and RES_OPTIONS controls resolver options that can influence DNS resolution behavior.
From an operational perspective, this vulnerability creates significant risks for system security and integrity. Local users who can execute setuid/setgid programs can potentially leverage this flaw to read arbitrary files on the system by manipulating the aforementioned environmental variables. The impact extends beyond simple information disclosure, as attackers could potentially access sensitive configuration files, user data, or system resources that should normally be restricted. This vulnerability directly violates the principle of least privilege and can lead to privilege escalation scenarios where unprivileged users gain elevated system access. The attack vector is particularly concerning because it requires only local access and does not depend on network connectivity or external attack surfaces.
Security professionals should note that this vulnerability aligns with CWE-250, which describes "Execute Code with Unusual or Unanticipated Privileges" and relates to improper handling of environment variables in privileged contexts. The flaw also connects to ATT&CK technique T1068, "Exploitation for Privilege Escalation," as it provides a method for local users to escalate their privileges through the manipulation of system libraries. Organizations should prioritize updating their glibc implementations to versions that properly clear these environmental variables during setuid/setgid execution, as this represents a fundamental security control failure in the system's privilege management mechanism.
The mitigation strategy involves immediate patching of affected glibc versions to ensure proper environment variable sanitization during privilege transitions. System administrators should also implement monitoring for unusual environmental variable usage patterns and conduct regular security audits to verify that setuid/setgid programs properly handle environmental variables. Additionally, implementing least privilege principles and reducing the number of setuid/setgid programs on systems can minimize the attack surface for this and similar vulnerabilities. The vulnerability demonstrates the critical importance of proper environment variable handling in security-sensitive contexts and underscores the need for comprehensive security testing of system libraries that handle privilege transitions.