CVE-2007-6131 in scanbuttond
Summary
by MITRE
buttonpressed.sh in scanbuttond 0.2.3 allows local users to overwrite arbitrary files via a symlink attack on the (1) scan.pnm and (2) scan.jpg temporary files.
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Analysis
by VulDB Data Team • 11/05/2017
The vulnerability identified as CVE-2007-6131 affects scanbuttond version 0.2.3, a daemon designed to handle scanning operations through button presses on multifunction devices. This issue manifests as a race condition vulnerability in the buttonpressed.sh script that processes scanner button events. The flaw occurs when the script creates temporary image files named scan.pnm and scan.jpg without proper security checks, making it susceptible to symlink attacks that can be exploited by local users to overwrite arbitrary files on the system.
The technical implementation of this vulnerability stems from the insecure creation of temporary files in the buttonpressed.sh script. When scanbuttond processes a button press event, it generates temporary files in predictable locations without validating whether these files already exist as symbolic links. An attacker can create malicious symbolic links with the same names as the expected temporary files before the legitimate script executes, causing the script to write data to the target file specified by the symbolic link rather than the intended temporary location. This represents a classic race condition vulnerability where the timing of file operations creates a window for exploitation.
The operational impact of this vulnerability extends beyond simple file overwriting capabilities, as it provides local attackers with the ability to modify critical system files, configuration data, or even execute arbitrary code through carefully crafted symbolic link targets. The vulnerability affects any local user who can execute the scanbuttond service or has access to the system where the daemon is running, potentially leading to privilege escalation if the daemon executes with elevated privileges. This type of vulnerability falls under CWE-367, which specifically addresses Time-of-Check to Time-of-Use (TOCTOU) race conditions, and aligns with ATT&CK technique T1059 for executing commands through system services.
Mitigation strategies for this vulnerability should focus on eliminating the race condition by implementing secure temporary file creation practices. The recommended approach involves using secure file creation methods that ensure atomic operations, such as creating temporary files with unique names and proper permissions, or employing the open() system call with appropriate flags to prevent symlink attacks. Additionally, the script should validate file existence and permissions before writing to temporary locations, and the scanbuttond service should be configured to run with minimal necessary privileges. Organizations should also consider implementing file system access controls and monitoring for suspicious symbolic link creation patterns to detect potential exploitation attempts. The vulnerability demonstrates the importance of secure coding practices in system services and highlights the need for proper temporary file handling in daemon applications.