CVE-2025-7786 is a cross-site scripting (XSS) vulnerability identified in Gnuboard g6, a popular open-source bulletin board system widely used for community forums and content management. The vulnerability affects all versions up to and including 6.0.10. Specifically, the flaw exists in the processing of the /bbs/scrap_popin_update/qa/ endpoint within the Post Reply Handler component. This endpoint fails to properly sanitize user-supplied input, allowing an attacker to inject malicious scripts that execute in the context of the victim's browser. The vulnerability is remotely exploitable without authentication, requiring only user interaction (e.g., clicking a crafted link or visiting a malicious page) to trigger the attack. The CVSS v4.0 base score is 5.1, indicating a medium severity level. The vector details show that the attack vector is network-based (AV:N), with low attack complexity (AC:L), no privileges required (PR:L, meaning low privileges but some authentication may be needed), and user interaction is necessary (UI:P). The impact affects integrity and availability to a limited extent, with no confidentiality impact. Although no public exploits are currently known in the wild, the vulnerability has been publicly disclosed, increasing the risk of exploitation. The lack of official patches at the time of disclosure means that affected organizations must implement interim mitigations to reduce exposure. This vulnerability could be leveraged to perform session hijacking, defacement, or phishing attacks by injecting malicious JavaScript, potentially compromising user accounts and trust in affected web applications.

For European organizations using Gnuboard g6 for forums, community portals, or internal communication platforms, this XSS vulnerability poses a significant risk. Successful exploitation could lead to theft of session cookies, enabling attackers to impersonate legitimate users, including administrators. This could result in unauthorized actions, data manipulation, or further compromise of internal systems. The injected scripts could also be used to deliver malware or redirect users to malicious sites, impacting user trust and organizational reputation. Given the remote exploitability and lack of required privileges, attackers could target a wide range of users, including employees and customers. The medium severity score reflects moderate impact, but the potential for chained attacks (e.g., leveraging XSS to escalate privileges or conduct social engineering) increases the threat level. European organizations in sectors such as education, government, and SMEs that rely on Gnuboard for community engagement are particularly vulnerable. Additionally, the public disclosure without available patches heightens the urgency for mitigation to prevent exploitation.

1. Immediate mitigation should include implementing Web Application Firewall (WAF) rules to detect and block malicious payloads targeting the /bbs/scrap_popin_update/qa/ endpoint. 2. Apply strict Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts in browsers. 3. Sanitize and validate all user inputs on the server side, especially those processed by the Post Reply Handler, to neutralize malicious code. 4. Monitor web server logs for unusual requests or payloads indicative of XSS attempts. 5. Limit user privileges to the minimum necessary to reduce the impact of compromised accounts. 6. Educate users about the risks of clicking unknown links and encourage reporting suspicious activity. 7. Stay alert for official patches or updates from the Gnuboard project and apply them promptly once available. 8. Consider temporary disabling or restricting access to the vulnerable endpoint if feasible until a patch is released. 9. Conduct regular security assessments and penetration tests focusing on web application input validation.