CVE-2022-21691 in OnionShare
Summary
by MITRE • 01/19/2022
OnionShare is an open source tool that lets you securely and anonymously share files, host websites, and chat with friends using the Tor network. In affected versions chat participants can spoof their channel leave message, tricking others into assuming they left the chatroom.
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Analysis
by VulDB Data Team • 01/20/2022
The vulnerability identified as CVE-2022-21691 affects OnionShare, a widely used open source tool designed for secure and anonymous file sharing, website hosting, and instant messaging through the Tor network. This tool operates by leveraging the Tor anonymity network to provide users with privacy-preserving communication channels while maintaining the integrity of their online activities. The security implications of this flaw extend beyond simple data integrity concerns, as it directly impacts the trust mechanisms within the application's chat functionality.
The technical flaw manifests in the chatroom leave message handling mechanism where malicious participants can forge or spoof their departure notifications. This allows attackers to manipulate the chatroom state information, creating false impressions that legitimate users have exited the conversation when they have actually remained active. The vulnerability stems from insufficient validation of leave message authenticity within the application's protocol implementation, enabling unauthorized modification of chatroom membership status updates. This type of flaw falls under the category of message integrity violations and can be classified as a CWE-284 Access Control vulnerability, where improper access control mechanisms allow unauthorized modification of system state information.
The operational impact of this vulnerability is significant for users relying on OnionShare for secure communications, as it undermines the fundamental trust assumptions within the chat system. When participants cannot accurately determine who is currently active in a chatroom, it creates opportunities for social engineering attacks, misdirection of communications, and potential exploitation of the remaining participants' trust. Attackers could use this vulnerability to create false impressions of chatroom abandonment, potentially leading to the exposure of sensitive information or manipulation of group dynamics. The attack surface expands particularly in environments where OnionShare is used for sensitive discussions or collaborative work, as the integrity of user presence information becomes compromised.
Mitigation strategies for CVE-2022-21691 should focus on implementing proper message authentication and validation mechanisms within the chat protocol. Users should upgrade to patched versions of OnionShare that address this vulnerability through cryptographic message signing or other authentication mechanisms that verify the legitimacy of leave messages. The fix should incorporate timestamp validation and message integrity checks to prevent spoofing attempts, aligning with ATT&CK technique T1566 Credential Access through manipulation of communication protocols. Organizations utilizing OnionShare for secure communications should also implement additional monitoring of chatroom membership changes and establish procedures for verifying user presence information, particularly in high-risk operational environments where the integrity of communication channels is paramount for maintaining security posture.