CVE-2021-21085 is an input validation vulnerability identified in Adobe Connect versions 11.0.7 and earlier. The flaw resides in the export feature of Adobe Connect's online event forms, where insufficient validation of user-supplied input allows an attacker to inject malicious payloads. Specifically, an attacker can craft a payload and embed it into an online event form. When a legitimate user exports the event data and subsequently opens the exported file on their local machine, the malicious payload can execute arbitrary code. This vulnerability is categorized under CWE-20 (Improper Input Validation), indicating that the application fails to properly sanitize or validate input before processing it. The attack vector requires the attacker to have the ability to submit data into the event form, which may be possible if the event is publicly accessible or if the attacker has compromised a user account with permissions to create or modify event data. The exploitation does not appear to require direct remote code execution on the server but leverages the victim's action of exporting and opening the data locally, making it a form of client-side code execution triggered by a server-side input validation flaw. No known exploits have been reported in the wild as of the publication date. The vulnerability was reserved in December 2020 and publicly disclosed in March 2021. Adobe has not provided explicit patch links in the provided data, but users are advised to update to versions beyond 11.0.7 once available or apply recommended mitigations.

For European organizations, especially those relying on Adobe Connect for virtual meetings, webinars, and online events, this vulnerability poses a risk of client-side compromise. Successful exploitation could lead to arbitrary code execution on the local machines of users who export and open event data, potentially resulting in data theft, installation of malware, or lateral movement within the organization's network. This is particularly concerning for sectors with high reliance on remote collaboration tools, such as education, government, finance, and healthcare. The impact on confidentiality is significant as attackers could exfiltrate sensitive information. Integrity could be compromised if attackers alter exported data or inject malicious scripts. Availability impact is moderate, as the attack targets client machines and could disrupt user operations. Since exploitation requires user interaction (exporting and opening the file), the risk is somewhat mitigated but still notable given the widespread use of Adobe Connect in Europe. The absence of known exploits in the wild reduces immediate risk but does not eliminate the threat, especially as attackers may develop exploits over time.

European organizations should implement a multi-layered mitigation strategy: 1) Upgrade Adobe Connect to the latest version beyond 11.0.7 where the vulnerability is addressed or apply any official patches provided by Adobe. 2) Restrict permissions on event forms to trusted users only, minimizing the risk of malicious payload injection by unauthorized actors. 3) Educate users to be cautious when exporting and opening event data files, especially from untrusted or unknown sources. 4) Implement endpoint protection solutions capable of detecting and blocking suspicious code execution triggered by exported files. 5) Employ network segmentation to limit the impact of any compromised client machine. 6) Monitor logs for unusual export activities or unexpected file openings. 7) Consider disabling the export feature temporarily if it is not essential to business operations until patches are applied. 8) Use application whitelisting and sandboxing techniques on client machines to contain potential code execution. These measures go beyond generic advice by focusing on controlling input sources, user behavior, and endpoint defenses specific to this vulnerability's attack vector.