CVE-2001-1374 in Expect
Summary
by MITRE
expect before 5.32 searches for its libraries in /var/tmp before other directories, which could allow local users to gain root privileges via a Trojan horse library that is accessed by mkpasswd.
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Analysis
by VulDB Data Team • 04/30/2019
The vulnerability described in CVE-2001-1374 represents a classic privilege escalation issue stemming from improper library loading order within the expect utility. This flaw affects expect versions prior to 5.32 and demonstrates how insecure library search paths can be exploited by malicious actors to gain elevated system privileges. The vulnerability specifically manifests when expect searches for its required libraries in the /var/tmp directory before examining other standard library locations, creating a dangerous condition where attacker-controlled libraries can be loaded instead of legitimate system libraries.
The technical mechanism behind this vulnerability involves the dynamic library loading behavior of expect, which follows a predetermined search order for shared libraries. When expect executes commands such as mkpasswd, it performs library resolution in a manner that prioritizes /var/tmp over more secure locations like /usr/lib or /lib. This search order is problematic because /var/tmp is typically world-writable and accessible to unprivileged users, making it an ideal location for attackers to place malicious libraries that match the names of legitimate system libraries. The vulnerability is particularly dangerous because expect is often installed with setuid root permissions, meaning that any library loaded by expect will execute with root privileges.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass broader system compromise possibilities. Local users who can write to /var/tmp can place malicious libraries that will be executed with root privileges when expect is invoked, particularly during password management operations like mkpasswd. This creates a persistent backdoor mechanism that can be exploited repeatedly without requiring additional system access. The vulnerability also demonstrates how legacy software design decisions can create security holes that persist for years, as the improper library search order was likely inherited from older system architecture decisions that did not account for modern security requirements.
From a cybersecurity perspective, this vulnerability aligns with multiple attack patterns documented in the MITRE ATT&CK framework, particularly those related to privilege escalation and persistence mechanisms. The technique resembles credential access methods where attackers leverage system utilities with elevated permissions to execute malicious code. The vulnerability also relates to CWE-427 Uncontrolled Search Path Element, which specifically addresses the issue of programs searching in insecure locations for required libraries. This weakness is further compounded by the fact that expect is commonly used in system administration tasks, making it a valuable target for attackers seeking persistent access to compromised systems. Organizations should implement immediate mitigations including updating expect to version 5.32 or later, restricting write permissions to /var/tmp, and monitoring for unauthorized library modifications in system directories.
The remediation approach for this vulnerability requires both immediate patching and long-term architectural improvements to library loading mechanisms. System administrators should prioritize updating the expect package to version 5.32 or newer, which corrects the library search order behavior. Additionally, security hardening measures should include implementing proper file permissions on /var/tmp to prevent unauthorized library placement, and establishing monitoring procedures for suspicious library modifications. The vulnerability also underscores the importance of secure coding practices and proper library management in system utilities, particularly those with elevated privileges. Organizations should conduct comprehensive audits of their system utilities to identify other programs with similar library search path vulnerabilities, as this issue is not unique to expect and may be present in other system utilities that follow insecure library loading patterns.