CVE-2017-18925 in opentmpfiles
Summary
by MITRE • 10/26/2020
opentmpfiles through 0.3.1 allows local users to take ownership of arbitrary files because d entries are mishandled and allow a symlink attack.
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Analysis
by VulDB Data Team • 11/27/2020
The vulnerability identified as CVE-2017-18925 affects the opentmpfiles utility version 0.3.1 and earlier, presenting a significant local privilege escalation risk through improper handling of directory entries. This flaw enables malicious local users to gain unauthorized ownership of arbitrary files within the system, creating potential security breaches that could compromise system integrity and data confidentiality.
The technical root cause stems from the mishandling of d entries within the opentmpfiles utility, which creates a symlink attack vector. When the utility processes directory entries, it fails to properly validate or sanitize symbolic links, allowing attackers to manipulate the file system traversal process. This vulnerability operates under the principle of time-of-check to time-of-use race conditions, where the utility checks for directory entry existence and then performs operations on those entries without proper validation of the symbolic link state between checks. The flaw specifically relates to CWE-367, which addresses Time-of-Check to Time-of-Use race conditions, and CWE-264, which covers permissions, privileges, and access controls.
The operational impact of this vulnerability is substantial as it allows local attackers with minimal privileges to escalate their access level and gain ownership of critical system files or user data. An attacker could exploit this weakness to modify sensitive configuration files, inject malicious code into system processes, or manipulate file permissions to maintain persistent access. The vulnerability affects systems where opentmpfiles is installed and actively used, potentially compromising the entire system if exploited successfully. This type of attack aligns with ATT&CK technique T1068, which covers local privilege escalation through race conditions, and T1003, which involves credential access through file system manipulation.
Mitigation strategies should focus on immediate patching of the opentmpfiles utility to version 0.3.2 or later, which contains the necessary fixes for the symlink handling issue. System administrators should also implement proper file system permissions and access controls, ensuring that the utility runs with minimal required privileges. Additional protective measures include monitoring for unauthorized file ownership changes, implementing proper symlink validation in system utilities, and conducting regular security audits of file system access patterns. Organizations should also consider implementing automated patch management systems to ensure timely updates of vulnerable utilities and maintain compliance with security standards such as those outlined in the NIST Cybersecurity Framework and ISO 27001 requirements for access control and system integrity.