CVE-2015-5701 in mktexlsr
Summary
by MITRE
mktexlsr revision 36855, and before revision 36626 as packaged in texlive allows local users to write to arbitrary files via a symlink attack. NOTE: this vulnerability exists due to the reversion of a fix of CVE-2015-5700.
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Analysis
by VulDB Data Team • 11/10/2019
The vulnerability described in CVE-2015-5701 represents a significant security flaw in the mktexlsr utility within the TeX Live distribution ecosystem. This utility is responsible for maintaining the TeX directory structure and is commonly used to update the file database that TeX systems use to locate installed packages and files. The issue manifests as a local privilege escalation vulnerability that allows attackers with low-privilege accounts to write to arbitrary files on the system through a carefully crafted symlink attack. This vulnerability specifically affects versions of mktexlsr between revision 36626 and 36855, with the problem occurring due to a regression in the codebase that reverted a previously implemented fix for CVE-2015-5700, creating a dangerous inconsistency in the system's file handling behavior.
The technical implementation of this vulnerability exploits the fundamental principle of symlink race conditions in Unix-like operating systems. When mktexlsr processes directory structures, it creates temporary files and symbolic links during its operation. The flaw occurs when the utility does not properly validate or sanitize the symbolic links it encounters, allowing an attacker to create malicious symlinks that point to sensitive system files or directories. During the execution of mktexlsr, when the utility processes these crafted symlinks, it writes data to the targets of these links rather than to intended temporary locations, effectively enabling arbitrary file write operations. This type of vulnerability falls under the CWE-376 category of "Improper Neutralization of Special Elements in Output Used by a Downstream Component" and specifically aligns with CWE-22, "Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')", as the attacker can traverse and write to locations outside of the intended scope.
The operational impact of CVE-2015-5701 extends beyond simple local file modification, as it can be leveraged to compromise the integrity of the entire TeX Live installation and potentially affect the broader system. An attacker could use this vulnerability to modify critical system files, inject malicious code into LaTeX packages, or corrupt the directory structure that TeX systems rely upon for proper operation. The vulnerability is particularly concerning in multi-user environments where users may have access to TeX Live utilities but should not possess write permissions to system-critical files. From an ATT&CK framework perspective, this vulnerability maps to T1059.007 "Command and Scripting Interpreter: PowerShell" and T1068 "Exploitation for Privilege Escalation" techniques, as it provides a mechanism for local privilege escalation through exploitation of a path traversal vulnerability in a system utility. The vulnerability also relates to T1548.001 "Abuse Elevation Control Mechanism: Setuid and Setgid" as it enables unauthorized modification of system files that may have elevated privileges.
The mitigation strategy for CVE-2015-5701 requires immediate attention through software updates and system hardening measures. Organizations should upgrade to mktexlsr revision 36626 or later, which contains the proper fix for the original CVE-2015-5700 vulnerability. Additionally, system administrators should implement proper file permissions and access controls for TeX Live directories, ensuring that only authorized users can execute mktexlsr and that temporary file creation occurs in secure, isolated locations. The vulnerability highlights the importance of proper input validation and the dangers of code regression, where fixes are inadvertently reverted during development cycles. Security monitoring should include detection of suspicious file modification patterns in TeX Live directories, particularly around temporary files and symbolic link creation. The vulnerability also underscores the necessity of maintaining comprehensive patch management procedures and the importance of understanding the complete impact of code changes, especially when reverting fixes for previously identified security issues.