CVE-2017-18869 in chownr
Summary
by MITRE
A TOCTOU issue in the chownr package before 1.1.0 for Node.js 10.10 could allow a local attacker to trick it into descending into unintended directories via symlink attacks.
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Analysis
by VulDB Data Team • 04/22/2023
The vulnerability identified as CVE-2017-18869 represents a classic time-of-check to time-of-use security flaw within the chownr package version 1.1.0 and earlier for Node.js environments. This type of vulnerability falls under the CWE-367 category, which specifically addresses Time-of-Check to Time-of-Use race conditions that can lead to security exploits. The chownr package, designed to recursively change file ownership in Node.js applications, suffers from a critical design flaw that allows local attackers to manipulate symbolic links during the execution process.
The technical implementation of this vulnerability occurs when the chownr package performs directory traversal operations without proper validation of symbolic link integrity. During the time-of-check phase, the system verifies directory permissions and access controls before proceeding with the actual file operations. However, between this verification and the time-of-use execution phase, an attacker can manipulate the filesystem by creating or modifying symbolic links that point to unintended target directories. This manipulation causes the chownr package to descend into directories that were not originally intended for ownership modification, effectively bypassing the intended access control mechanisms.
The operational impact of this vulnerability extends beyond simple privilege escalation as it enables attackers to potentially modify ownership of critical system files or directories that they would normally not have access to. This can lead to persistent unauthorized access to system resources and compromise the integrity of the file system. The vulnerability is particularly dangerous in multi-user environments where attackers can exploit this weakness to gain elevated privileges or manipulate sensitive data. The attack vector specifically targets local users who can leverage the symlink manipulation to redirect the chownr package's operations to arbitrary locations within the filesystem.
From a threat modeling perspective, this vulnerability aligns with ATT&CK technique T1068 which involves exploiting local privileges to gain system access through race conditions and file system manipulation. The attack requires minimal privileges and can be executed through standard user accounts, making it particularly concerning for system administrators. Organizations using Node.js applications that rely on chownr for file management operations are at risk of unauthorized file system modifications, potentially leading to complete system compromise. The vulnerability demonstrates the critical importance of proper input validation and atomic operations in file system manipulation utilities.
Mitigation strategies for CVE-2017-18869 involve immediate upgrading to chownr version 1.1.0 or later, which implements proper symlink resolution and validation mechanisms. System administrators should also implement comprehensive file system monitoring to detect unauthorized symbolic link modifications and establish regular security audits of Node.js applications. Additional protective measures include restricting write permissions on directories that are commonly traversed by chownr operations and implementing proper access control lists to limit potential impact of successful exploitation attempts. The fix addresses the underlying race condition by ensuring that symbolic link checks are performed atomically with the actual file operations, preventing the manipulation window that previously enabled this attack vector.