CVE-2022-21695 is a medium-severity vulnerability classified under CWE-287 (Improper Authentication) affecting versions of OnionShare prior to 2.5. OnionShare is an open-source application designed to enable secure and anonymous file sharing, website hosting, and chat communication over the Tor network. The vulnerability allows authenticated users, or even unauthenticated users in public mode, to send chat messages without being listed as visible participants in the chat session. This flaw undermines the integrity of participant visibility and authentication mechanisms within OnionShare's chat functionality. Essentially, it permits a user to masquerade as a hidden participant, potentially enabling covert communication or unauthorized message injection without detection by other users. The issue was addressed and resolved in OnionShare version 2.5. No known exploits have been reported in the wild to date. The vulnerability does not appear to require elevated privileges beyond normal user access, and it affects all versions prior to 2.5. Given OnionShare’s reliance on the Tor network for anonymity, this improper authentication could be exploited to bypass expected participant transparency in chat sessions, potentially facilitating malicious activities such as misinformation, unauthorized data exchange, or evasion of accountability within the communication channel.

For European organizations, the impact of this vulnerability depends largely on the extent to which OnionShare is used for sensitive communications or data exchange. Organizations leveraging OnionShare for secure, anonymous collaboration or file sharing could face risks related to unauthorized message injection or covert communication by hidden participants. This could lead to misinformation, data leakage, or manipulation of communication flows without detection. While OnionShare is primarily used for privacy-focused communications, sectors such as journalism, human rights groups, and certain research entities in Europe that rely on anonymity and secure messaging could be particularly affected. The vulnerability compromises the integrity and non-repudiation aspects of communication, potentially undermining trust in the platform. However, since no known exploits are reported and the vulnerability requires at least user-level access or public mode usage, the overall risk to large enterprises or critical infrastructure is limited unless OnionShare is explicitly used in their workflows. The availability and confidentiality of the system are not directly impacted by this flaw, but the integrity of chat communications is at risk.

To mitigate this vulnerability, European organizations and users should upgrade OnionShare installations to version 2.5 or later, where the issue has been resolved. For environments where immediate upgrading is not feasible, organizations should consider disabling the chat functionality or restricting access to trusted users only, especially avoiding public mode usage. Monitoring chat logs and participant lists for anomalies could help detect suspicious hidden participants. Additionally, organizations should educate users about the risks of using outdated OnionShare versions and encourage strict operational security practices when sharing sensitive information. Network-level controls could be implemented to limit OnionShare usage to authorized endpoints. Finally, integrating OnionShare usage policies within broader organizational security frameworks will help ensure that only vetted users can leverage the tool, reducing the risk of exploitation.