CVE-2015-3339 in Linux
Summary
by MITRE
Race condition in the prepare_binprm function in fs/exec.c in the Linux kernel before 3.19.6 allows local users to gain privileges by executing a setuid program at a time instant when a chown to root is in progress, and the ownership is changed but the setuid bit is not yet stripped.
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Analysis
by VulDB Data Team • 05/09/2022
The vulnerability identified as CVE-2015-3339 represents a critical race condition within the Linux kernel's execve system call handling mechanism. This flaw exists in the prepare_binprm function located in fs/exec.c and affects Linux kernel versions prior to 3.19.6. The race condition occurs during the execution of setuid programs when the kernel performs a chown operation to root while simultaneously processing the setuid bit removal. This timing issue creates a brief window where malicious users can exploit the system to escalate privileges through carefully timed execution sequences.
The technical exploitation of this vulnerability relies on the specific temporal sequence between file ownership changes and setuid bit manipulation. When a setuid program is executed, the kernel first changes the file ownership to root through the chown operation, but the setuid bit removal process occurs in a subsequent step. During this brief interval between ownership change and bit stripping, an attacker can execute a malicious program that leverages the transitional state to gain elevated privileges. The race condition typically manifests when the kernel's file permission checks occur before the setuid bit is properly cleared, allowing the execution of programs with root privileges despite not having the proper authorization.
This vulnerability significantly impacts system security by providing local users with a method to bypass privilege separation mechanisms that are fundamental to Linux security architecture. The exploitation directly violates the principle of least privilege and undermines the integrity of the setuid mechanism, which is designed to allow specific programs to run with elevated privileges while maintaining overall system security. The attack vector specifically targets local users who have the ability to execute programs, making it particularly dangerous in multi-user environments where privilege escalation can lead to complete system compromise.
The operational impact of CVE-2015-3339 extends beyond simple privilege escalation, as it represents a fundamental flaw in the kernel's security model that affects all systems running vulnerable kernel versions. This vulnerability aligns with CWE-362, which describes race conditions in security-critical code paths, and can be mapped to ATT&CK technique T1068, which covers privilege escalation through local exploits. Organizations running affected kernel versions face significant risk of unauthorized access and potential complete system compromise, as the vulnerability allows attackers to execute arbitrary code with root privileges without requiring network access or external attack vectors.
Mitigation strategies for this vulnerability primarily focus on kernel updates and system hardening measures. The most effective solution is upgrading to Linux kernel version 3.19.6 or later, where the race condition has been resolved through improved synchronization mechanisms in the prepare_binprm function. System administrators should also implement additional security controls such as restricting setuid programs, monitoring for suspicious execution patterns, and applying the principle of least privilege to limit user capabilities. The vulnerability demonstrates the importance of proper race condition handling in security-critical kernel code and highlights the necessity of thorough testing and validation of security mechanisms before deployment.