CVE-2022-21689 is a vulnerability classified under CWE-400, indicating uncontrolled resource consumption, found in OnionShare versions prior to 2.5. OnionShare is an open-source application that enables secure and anonymous file sharing, website hosting, and chat over the Tor network. The vulnerability specifically affects the receive mode of OnionShare, which limits concurrent uploads to 100 per second. An attacker can exploit this by using a simple script to trigger the upload limit repeatedly within the same second, effectively blocking other users from uploading files. This denial-of-service (DoS) condition arises because the application enforces a strict cap on concurrent uploads per second and does not differentiate between legitimate and malicious upload attempts. Due to the anonymity and privacy features inherent in the Tor network, mitigating this attack in public mode is challenging, as it is difficult to identify or block malicious actors without compromising anonymity. The vulnerability does not require authentication, as it can be triggered by any user with access to the receive mode endpoint. No known exploits have been reported in the wild, and no official patches were linked in the provided information, although the issue is addressed in versions 2.5 and later. The attack impacts availability by preventing legitimate users from uploading files, but it does not directly compromise confidentiality or integrity of data. The scope is limited to OnionShare users operating in receive mode, particularly those using versions earlier than 2.5.

For European organizations using OnionShare, especially those relying on it for secure and anonymous file sharing or communication, this vulnerability could disrupt critical workflows by denying service to legitimate users. Organizations in sectors such as journalism, human rights advocacy, and secure communications—where OnionShare is popular due to its privacy features—may experience operational delays or interruptions. The inability to upload files could hinder information exchange and collaboration, particularly in sensitive environments requiring anonymity. While the vulnerability does not lead to data breaches or unauthorized data modification, the denial-of-service aspect could degrade trust in the tool and force users to seek less secure alternatives. Additionally, the anonymity of the Tor network complicates detection and mitigation, potentially allowing persistent attackers to cause prolonged service disruption. The impact is more pronounced for organizations that depend on OnionShare for time-sensitive or critical data transfers.

To mitigate this vulnerability, European organizations should upgrade OnionShare to version 2.5 or later, where this issue is addressed. Since no patch links were provided, users should verify the latest official releases from the OnionShare project. In environments where upgrading is not immediately possible, organizations can implement rate limiting or connection throttling at the network level to restrict the number of concurrent upload attempts from individual IP addresses, although this may be less effective due to Tor's anonymity. Monitoring network traffic patterns for unusual spikes in upload requests can help detect potential abuse. Deploying additional application-layer protections, such as CAPTCHA challenges or requiring authentication in private modes, can reduce the risk of automated abuse, though these may not be feasible in public anonymous modes. Finally, organizations should educate users about this limitation and encourage the use of updated software versions to maintain service availability.