CVE-2016-5026 in OnionShare
Summary
by MITRE
hs.py in OnionShare before 0.9.1 allows local users to modify the hiddenservice by pre-creating the /tmp/onionshare directory.
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Analysis
by VulDB Data Team • 09/28/2024
The vulnerability described in CVE-2016-5026 represents a significant security flaw in the OnionShare application version 0.9.0 and earlier. This issue stems from improper handling of temporary directories during the hidden service creation process, creating a path traversal and privilege escalation opportunity for local attackers. The vulnerability specifically affects the hs.py script which manages the hidden service configuration, allowing malicious users to manipulate the system's hidden service setup by leveraging the /tmp/onionshare directory structure. This weakness enables attackers to potentially gain unauthorized access to the hidden service configuration files and modify their contents in ways that could compromise the anonymity and security of the service.
The technical root cause of this vulnerability lies in the application's insufficient validation and sanitization of temporary file paths during the hidden service initialization process. When OnionShare creates its temporary directory structure, it fails to properly secure the /tmp/onionshare location, allowing local users to pre-create this directory with malicious content or permissions. This design flaw falls under the category of insecure temporary file handling, which is commonly associated with CWE-377 and CWE-378. The application's failure to implement proper directory permissions and atomic operations during temporary file creation creates a race condition that attackers can exploit to inject malicious code or modify critical service configuration data.
The operational impact of this vulnerability extends beyond simple privilege escalation to potentially compromise the entire anonymity infrastructure that OnionShare provides. An attacker who successfully exploits this vulnerability could modify the hidden service's configuration, redirect traffic, or even inject malicious content that would be served through the hidden service. This threat is particularly concerning in environments where OnionShare is used for sensitive communications, as it could allow adversaries to monitor or manipulate the data being transmitted through the anonymized network. The vulnerability also represents a significant risk to the integrity of the hidden service's identity and operational parameters, potentially leading to service disruption or complete compromise of the anonymity network.
Mitigation strategies for this vulnerability require immediate implementation of proper directory handling procedures within the OnionShare application. The recommended approach involves implementing atomic directory creation with proper permission settings, ensuring that temporary directories are created with restrictive permissions and are not susceptible to pre-creation by unauthorized users. Security best practices dictate that applications should verify the existence and ownership of temporary directories before proceeding with configuration operations, and should implement proper file system access controls to prevent unauthorized modifications. This vulnerability aligns with ATT&CK technique T1059.007 for privilege escalation and T1566 for credential access, highlighting the need for comprehensive security controls that address both local and network-level threats. System administrators should ensure immediate patching of affected versions and implement monitoring for unauthorized modifications to temporary directories in environments where OnionShare is deployed.