CVE-2006-1695 in Fbida
Summary
by MITRE
The fbgs script in the fbi package 2.01-1.4, when the TMPDIR environment variable is not defined, allows local users to overwrite arbitrary files via a symlink attack on temporary files in /var/tmp/fbps-[PID].
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Analysis
by VulDB Data Team • 06/17/2019
The vulnerability identified as CVE-2006-1695 resides within the fbgs script component of the fbi package version 2.01-1.4, representing a classic file system race condition and symlink attack vector that enables local privilege escalation. This flaw specifically manifests when the TMPDIR environment variable remains undefined during script execution, creating a predictable temporary file creation pattern that adversaries can exploit to gain unauthorized access to system resources.
The technical implementation of this vulnerability stems from improper handling of temporary file creation processes within the fbgs script. When TMPDIR is not explicitly set, the script defaults to using /var/tmp/fbps-[PID] as the temporary file location, where [PID] represents the process identifier. This predictable naming convention creates a window of opportunity for attackers to establish symbolic links in the temporary directory before the script creates its actual temporary files, thereby enabling them to redirect the script's write operations to arbitrary locations on the file system.
This vulnerability directly maps to CWE-377: Insecure Temporary File creation and CWE-378: Creation of Temporary File With Insecure Permissions, both of which fall under the broader category of insecure file handling practices. The attack vector operates through the fundamental principle of time-of-check to time-of-use (TOCTOU) race conditions, where the system checks for file existence or permissions at one point in time and then uses the file at a later point, allowing an attacker to manipulate the file system state between these two operations. The vulnerability also aligns with ATT&CK technique T1059.007 for Scripting and T1548.002 for Abuse of Functionality, as it leverages legitimate system scripts to execute malicious file operations.
The operational impact of this vulnerability extends beyond simple file overwriting capabilities, as it provides attackers with the means to modify critical system files, potentially leading to privilege escalation or persistent access. Local users who can execute the fbgs script can leverage this flaw to overwrite files with malicious content, potentially compromising system integrity and confidentiality. The vulnerability affects systems running the specific version of the fbi package mentioned, particularly those where the TMPDIR environment variable is not properly configured or enforced.
Mitigation strategies for this vulnerability require immediate attention through patching the affected fbi package to version 2.01-1.5 or later, which includes proper temporary file handling mechanisms. System administrators should also implement proper environment variable configuration to ensure TMPDIR is consistently set with secure permissions, typically using directories with restricted access permissions. Additionally, implementing proper file system permissions and using secure temporary file creation methods such as mkstemp() or similar secure functions can prevent similar vulnerabilities from occurring in other applications. Organizations should conduct thorough vulnerability assessments to identify other applications using similar insecure temporary file creation patterns and apply the principle of least privilege to temporary file operations. The vulnerability also underscores the importance of proper input validation and secure coding practices in preventing race condition exploits that can compromise system security and integrity.