CVE-1999-1541 in Shell-Lock
Summary
by MITRE
shell-lock in Cactus Software Shell Lock allows local users to read or modify decoded shell files before they are executed, via a symlink attack on a temporary file.
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Analysis
by VulDB Data Team • 04/19/2026
The vulnerability described in CVE-1999-1541 represents a critical race condition and privilege escalation flaw within the Cactus Software Shell Lock utility. This issue specifically affects the handling of temporary files during shell script execution processes, creating a window of opportunity for local attackers to manipulate system resources before they are properly secured. The vulnerability stems from improper file handling mechanisms that fail to adequately protect temporary files from symbolic link attacks, allowing malicious users to intercept or modify sensitive shell script contents during execution. Such flaws typically arise from inadequate security considerations during the development phase of system utilities, particularly those involved in privilege escalation or shell execution contexts.
The technical implementation of this vulnerability exploits a classic symlink attack pattern where an attacker creates a symbolic link to a target file before the legitimate process creates the actual temporary file. In the context of shell lock utilities, this typically occurs when the application creates temporary files in predictable locations without proper atomic creation mechanisms or file permission controls. The flaw allows attackers to substitute their own content for the intended shell script, enabling them to execute arbitrary code with elevated privileges or access sensitive system information. This type of vulnerability aligns with CWE-367, which specifically addresses Time-of-Check to Time-of-Use (TOCTOU) race conditions, and represents a common pattern in Unix-like systems where temporary file creation lacks proper security controls.
The operational impact of CVE-1999-1541 extends beyond simple privilege escalation to encompass potential system compromise and data integrity violations. Local users who can exploit this vulnerability gain the ability to modify shell scripts before execution, potentially allowing them to inject malicious commands, modify system configurations, or access restricted files. The attack vector requires local system access but can result in significant security implications, particularly in multi-user environments where privilege separation is crucial. This vulnerability can be exploited to bypass security controls implemented by shell lock utilities, undermining the fundamental security assumptions of the system. The attack typically succeeds because the system does not properly validate the integrity of temporary files or ensure atomic file creation processes, creating a window where symbolic links can be manipulated without proper authorization.
Mitigation strategies for this vulnerability require implementing proper file handling mechanisms that prevent race conditions during temporary file creation. System administrators should ensure that shell lock utilities are updated to versions that implement atomic file creation using secure temporary file creation functions such as mkstemp or similar secure APIs. The implementation should avoid predictable temporary file names and ensure that temporary files are created with appropriate permissions and ownership. Additionally, the system should validate that temporary files are not symbolic links before processing them, and implement proper file access controls to prevent unauthorized modification. This vulnerability highlights the importance of following secure coding practices as outlined in the OWASP Secure Coding Guidelines and aligns with ATT&CK technique T1068, which covers privilege escalation through race conditions. Organizations should also implement regular security assessments to identify similar vulnerabilities in legacy system components and ensure that all temporary file handling follows established security standards to prevent similar issues from occurring in modern implementations.