CVE-2012-3440 in sudo
Summary
by MITRE
A certain Red Hat script for sudo 1.7.2 on Red Hat Enterprise Linux (RHEL) 5 allows local users to overwrite arbitrary files via a symlink attack on the /var/tmp/nsswitch.conf.bak temporary file.
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Analysis
by VulDB Data Team • 03/27/2021
The vulnerability described in CVE-2012-3440 represents a critical privilege escalation flaw within the sudo package version 1.7.2 running on Red Hat Enterprise Linux 5 systems. This issue stems from improper handling of temporary files during the execution of administrative scripts, creating a dangerous race condition that local attackers can exploit to gain elevated system privileges. The vulnerability specifically affects the nsswitch.conf.bak file located in the /var/tmp directory, which serves as a backup mechanism for the Name Service Switch configuration file that controls how the system resolves names and addresses.
The technical implementation of this vulnerability involves a symlink attack that exploits the predictable naming pattern and insecure temporary file creation process. When the sudo script executes, it creates a temporary backup file named nsswitch.conf.bak in the /var/tmp directory without proper security checks or atomic operations. An attacker can manipulate the system by creating a symbolic link from /var/tmp/nsswitch.conf.bak to a target file they wish to overwrite, such as a system configuration file or even a binary with elevated privileges. This race condition occurs because the script does not validate that the temporary file is actually created by the legitimate process rather than being a pre-existing symbolic link, allowing the attacker to redirect file operations to arbitrary locations.
The operational impact of this vulnerability extends far beyond simple file overwriting, as it provides local users with a pathway to escalate privileges and potentially gain root access to the affected system. Since the sudo package is commonly used for administrative tasks, an attacker who can successfully exploit this vulnerability can execute commands with elevated privileges, potentially compromising the entire system. The attack vector is particularly concerning because it requires minimal privileges to initiate and can be executed by any local user, making it an attractive target for both malicious actors and automated exploitation tools. This weakness undermines the fundamental security principle of least privilege and can lead to complete system compromise.
Mitigation strategies for CVE-2012-3440 should focus on immediate patching of the affected sudo package to version 1.7.3 or later, which includes proper temporary file handling mechanisms. Organizations should also implement proper file system permissions and ensure that temporary directories have appropriate security settings to prevent symbolic link creation by unprivileged users. The use of atomic file operations and proper validation of temporary file creation should be enforced throughout all administrative scripts. Additionally, system administrators should monitor for any unauthorized symbolic link creation in temporary directories and consider implementing file integrity monitoring solutions to detect potential exploitation attempts. This vulnerability aligns with CWE-377: Insecure Temporary File and CWE-378: Creation of Temporary File With Insecure Permissions, and represents a classic example of how improper file handling can create significant security risks. The attack pattern follows ATT&CK technique T1068: Exploitation for Privilege Escalation, demonstrating how local privilege escalation vulnerabilities can be leveraged to achieve system compromise.