CVE-2000-1108 in Midnight Commander
Summary
by MITRE
cons.saver in Midnight Commander (mc) 4.5.42 and earlier does not properly verify if an output file descriptor is a TTY, which allows local users to corrupt files by creating a symbolic link to the target file, calling mc, and specifying that link as a TTY argument.
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Analysis
by VulDB Data Team • 04/30/2019
The vulnerability described in CVE-2000-1108 resides within the cons.saver component of Midnight Commander version 4.5.42 and earlier, representing a classic case of improper input validation and privilege escalation through symbolic link manipulation. This flaw specifically targets the file descriptor verification mechanism that should ensure safe handling of output operations. The issue manifests when the application fails to properly validate whether an output file descriptor corresponds to a terminal device, creating a window of opportunity for malicious file corruption.
The technical exploitation of this vulnerability leverages a fundamental weakness in the application's security model where symbolic link traversal is not adequately protected against. When a local attacker creates a symbolic link pointing to a target file and subsequently invokes mc with this link as a TTY argument, the application's insufficient verification allows the attacker to write to the target file through the symbolic link. This represents a direct violation of the principle of least privilege and demonstrates a critical failure in the application's file system access controls. The flaw operates at the intersection of file descriptor handling and symbolic link security, where the application's assumption about device type validation proves incorrect.
The operational impact of this vulnerability extends beyond simple file corruption, as it enables persistent unauthorized modifications to system files and user data. Attackers can exploit this weakness to overwrite critical system files, modify configuration data, or inject malicious content into target files, potentially leading to privilege escalation or system compromise. The vulnerability affects local users only, but its implications are significant because it allows for covert file manipulation without direct system access. This type of vulnerability commonly falls under the CWE-22 category for Improper Limitation of a Pathname to a Restricted Directory, and can be mapped to ATT&CK technique T1068 for Exploitation for Privilege Escalation.
Mitigation strategies for CVE-2000-1108 should focus on implementing proper file descriptor validation and symbolic link resolution checks within the application. The most effective approach involves modifying the cons.saver component to explicitly verify that output file descriptors are indeed terminal devices before proceeding with file operations. This includes implementing checks for device type validation using system calls such as isatty() and ensuring that symbolic links are properly resolved and validated against the target file's security context. System administrators should also consider restricting symbolic link creation permissions in sensitive directories and implementing proper file system access controls. Additionally, upgrading to versions of Midnight Commander that have addressed this vulnerability represents the most reliable long-term solution, as the flaw stems from a design decision that was subsequently corrected in later releases. The vulnerability demonstrates the critical importance of input validation and proper privilege management in file handling operations, particularly in applications that process user-supplied file paths and descriptors.