CVE-2022-21649 is a stored Cross-Site Scripting (XSS) vulnerability identified in convos-chat, an open-source multi-user chat application that operates within web browsers. The vulnerability affects convos versions from 6.49 up to, but not including, 6.52. The root cause lies in improper input neutralization during web page generation, specifically CWE-79. In the chat interface, any text starting with "https://" is automatically converted into an HTML anchor (<a>) tag. While the application escapes angle brackets (< and >) to prevent injection, it fails to properly escape double quotes (") within the input. This omission allows an attacker to inject malicious JavaScript code via attributes such as onfocus or autofocus embedded within the anchor tag. When a user interacts with or focuses on the malicious link, the injected script executes in the context of the victim's browser session. This stored XSS can lead to session hijacking, credential theft, or unauthorized actions performed on behalf of the user. The vulnerability does not require user authentication to exploit, and no user interaction beyond focusing on the crafted link is necessary. Although no public exploits have been reported in the wild, the vulnerability poses a significant risk due to the persistent nature of stored XSS and the potential for widespread impact within chat environments. Users of affected convos versions are strongly advised to update to a patched version once available or implement immediate mitigations to prevent exploitation.

For European organizations utilizing convos-chat, particularly those relying on it for internal or external communications, this vulnerability can compromise confidentiality and integrity of communications. Attackers exploiting this flaw can execute arbitrary scripts in users' browsers, potentially stealing session tokens, credentials, or sensitive information exchanged in chats. This can lead to unauthorized access to organizational resources or data breaches. Additionally, the integrity of chat messages can be undermined, eroding trust in communication channels. Availability impact is limited but could occur if attackers leverage XSS to perform denial-of-service attacks on user sessions. Given the collaborative nature of chat applications, the vulnerability could facilitate lateral movement within networks if attackers gain access to privileged accounts. European organizations in sectors such as finance, government, healthcare, and critical infrastructure, where secure communication is paramount, face elevated risks. The medium severity rating reflects the balance between the ease of exploitation and the potential damage, but the stored nature of the XSS increases the risk of widespread impact within affected user communities.

1. Immediate upgrade: Organizations should prioritize upgrading convos-chat to a version beyond 6.52 where this vulnerability is patched. 2. Input sanitization enhancement: Until an official patch is available, implement server-side input validation and sanitization to escape or remove double quotes and other special characters in URLs before rendering them as HTML. 3. Content Security Policy (CSP): Deploy a strict CSP that restricts the execution of inline scripts and only allows scripts from trusted sources to reduce the impact of injected scripts. 4. User awareness: Educate users to avoid clicking on suspicious links within the chat application and report any unusual behavior. 5. Monitoring and logging: Enable detailed logging of chat messages and user interactions to detect potential exploitation attempts. 6. Web Application Firewall (WAF): Configure WAF rules to detect and block payloads containing suspicious attributes like onfocus or autofocus in chat messages. 7. Disable autofocus/onfocus attributes: If feasible, modify the application to disallow or sanitize these attributes in user-generated content. 8. Session management: Implement secure session handling practices, including HttpOnly and Secure cookies, to limit the impact of stolen session tokens.