CVE-2013-4235 in shadow
Summary
by MITRE
shadow: TOCTOU (time-of-check time-of-use) race condition when copying and removing directory trees
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Analysis
by VulDB Data Team • 04/10/2026
The vulnerability identified as CVE-2013-4235 represents a critical time-of-check time-of-use race condition flaw within the shadow password utilities, specifically affecting directory tree copying and removal operations. This weakness stems from the fundamental timing issue where a system checks the state of a resource and then uses that resource without revalidating the check, creating an exploitable window for malicious actors to manipulate the system state between verification and execution phases. The flaw is particularly dangerous because it affects core system utilities that manage user authentication and password operations, which are integral to system security and access control mechanisms.
The technical implementation of this vulnerability occurs within the shadow utilities that handle user account management and password operations. When these utilities perform directory tree operations, they first check if certain directories exist or meet specific criteria before proceeding with copy or removal actions. An attacker can exploit this by creating a race condition where they rapidly switch the state of the target directories between the check phase and the use phase. This allows malicious users to manipulate the system into performing operations on unintended targets or to bypass security checks that should prevent unauthorized access to sensitive system resources. The vulnerability specifically impacts the cp and rm commands when used with directory trees, where symbolic links and directory structures can be manipulated to exploit the temporal gap between validation and execution.
The operational impact of CVE-2013-4235 extends beyond simple privilege escalation to potentially enable complete system compromise through manipulation of user account management functions. Attackers can leverage this race condition to gain unauthorized access to system resources, modify user accounts, or even escalate privileges to root level access. The vulnerability affects systems running various Unix-like operating systems that utilize the shadow password utilities, making it particularly widespread across enterprise environments and server deployments where user authentication is critical. The flaw can be exploited in both local and remote attack scenarios, depending on the system configuration and the attacker's initial access level, potentially allowing for persistent backdoor establishment through manipulation of user account databases.
Mitigation strategies for this vulnerability require immediate patching of affected systems with the latest security updates from software vendors, as the flaw has been well-documented and remediated through official patches. System administrators should implement proper access controls and monitoring to detect unusual directory manipulation activities that might indicate exploitation attempts. The use of privilege separation mechanisms and mandatory access controls can help reduce the impact of successful exploitation attempts. Additionally, organizations should conduct comprehensive vulnerability assessments to identify systems running vulnerable versions of shadow utilities and ensure all systems are updated to prevent exploitation. This vulnerability aligns with CWE-367, which specifically addresses time-of-check to time-of-use race conditions, and maps to ATT&CK technique T1068 for local privilege escalation through system weakness exploitation, making it a critical concern for enterprise security teams implementing comprehensive threat detection and response strategies.