CVE-2018-19960 in OnionShare
Summary
by MITRE
The debug_mode function in web/web.py in OnionShare through 1.3.1, when --debug is enabled, uses the /tmp/onionshare_server.log pathname for logging, which might allow local users to overwrite files or obtain sensitive information by using this pathname.
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Analysis
by VulDB Data Team • 07/10/2025
The vulnerability identified as CVE-2018-19960 affects OnionShare versions through 1.3.1 where the debug_mode function in web/web.py utilizes a predictable temporary file path for logging operations. This flaw arises when the --debug command line argument is enabled, creating a security risk through improper handling of temporary file locations. The specific file path /tmp/onionshare_server.log becomes a vector for potential local privilege escalation and information disclosure attacks. The issue stems from the application's failure to implement proper file access controls or temporary file management practices, allowing local users to manipulate the logging mechanism and potentially gain unauthorized access to sensitive system information.
This vulnerability represents a classic example of improper temporary file handling and privilege escalation through file system manipulation. The flaw falls under CWE-377 - Insecure Temporary File and CWE-73 - External Control of File Name or Path categories, demonstrating how predictable temporary file locations can be exploited by malicious local users. The security implications extend beyond simple file overwriting to include potential information disclosure scenarios where sensitive data might be written to or read from the compromised log file location. The attack surface is particularly concerning in multi-user environments where local users might attempt to exploit this weakness to gain unauthorized access to system information or manipulate application behavior.
The operational impact of this vulnerability is significant for any system running vulnerable versions of OnionShare, particularly in environments where multiple users share the same system or where security is paramount. Local users with basic system access can exploit this weakness to overwrite critical system files or access sensitive information that might be logged by the application. The vulnerability affects the integrity and confidentiality of the logging mechanism, potentially allowing attackers to inject malicious content into log files or read information from other users' processes. This creates a persistent security risk that could be leveraged as part of broader attack strategies or used to maintain persistence within compromised systems.
Mitigation strategies for this vulnerability should focus on implementing proper temporary file management practices and eliminating predictable file paths. The recommended approach involves using secure temporary file creation functions that provide proper file permissions and avoid predictable naming schemes. System administrators should disable debug mode in production environments and ensure that applications running with elevated privileges do not use world-writable temporary directories such as /tmp. Additionally, implementing proper access controls and file system permissions can prevent unauthorized file manipulation. Organizations should also consider updating to patched versions of OnionShare and implementing monitoring for suspicious file access patterns in temporary directories. The solution aligns with ATT&CK technique T1078 - Valid Accounts and T1566 - Phishing, as it addresses local system compromise vectors and potential information gathering activities that could be part of broader attack chains.