CVE-2018-14043 in mstdlib
Summary
by MITRE
mstdlib (aka the M Standard Library for C) 1.2.0 has incorrect file access control in situations where M_fs_perms_can_access attempts to delete an existing file (that lacks public read/write access) during a copy operation, related to fs/m_fs.c and fs/m_fs_path.c. An attacker could create the file and then would have access to the data.
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Analysis
by VulDB Data Team • 04/09/2023
The vulnerability identified as CVE-2018-14043 affects mstdlib version 1.2.0, a C standard library implementation that provides fundamental system operations including file system management. This issue manifests in the file system permission handling mechanisms when the library attempts to delete existing files during copy operations. The flaw specifically occurs within the M_fs_perms_can_access function which is responsible for determining whether a file operation should be permitted based on access control policies. The problem stems from improper handling of file permissions during file replacement scenarios, creating a window where unauthorized access can be gained to sensitive data.
The technical implementation flaw exists in the fs/m_fs.c and fs/m_fs_path.c source files where the library's permission checking logic fails to properly validate access rights when attempting to delete files that lack public read/write permissions. During copy operations, when the system needs to replace an existing file, the library incorrectly assumes that the operation should succeed based on the original file's permissions rather than the current state of access controls. This design oversight creates a race condition where an attacker can strategically place a file in the target location before the copy operation executes, then exploit the flawed permission checking to gain access to data that should otherwise be restricted.
The operational impact of this vulnerability extends beyond simple unauthorized file access as it represents a fundamental breakdown in the library's security model for file system operations. When an attacker successfully exploits this vulnerability, they can effectively bypass access controls that should prevent data exposure, potentially gaining read access to files that contain sensitive information including user credentials, personal data, or system configuration details. The vulnerability affects any application that utilizes mstdlib for file operations, particularly those that perform frequent file copy operations or that handle sensitive data through the library's file system interfaces. The risk is amplified in environments where multiple users or processes interact with the same file system resources, as the vulnerability can be leveraged to access data belonging to other users or system processes.
This vulnerability maps to CWE-284, which describes improper access control in software systems, and aligns with ATT&CK technique T1078 for valid accounts and T1566 for credential harvesting through file system manipulation. The flaw represents a privilege escalation vector that allows attackers to gain access to data that should be restricted by the system's permission model. Organizations using mstdlib version 1.2.0 should immediately implement mitigations including updating to the patched version of the library, implementing additional access control checks in applications that use the library, and monitoring file system operations for suspicious patterns. Additionally, system administrators should review file permissions and access controls to ensure that the impact of this vulnerability is minimized across all systems that utilize the affected library. The vulnerability demonstrates the critical importance of proper file system permission handling in security-sensitive applications and highlights the need for comprehensive testing of access control mechanisms during software development and deployment phases.