CVE-2024-36676 is an access control vulnerability identified in BookStack, an open-source platform for creating documentation and wikis. The flaw exists in versions prior to 24.05.1 and stems from improper validation of user access rights on public-facing forms. Specifically, attackers can leverage these forms to confirm whether specific user accounts exist within the system, effectively enumerating valid users. Beyond user enumeration, the vulnerability enables attackers to trigger targeted notification emails repeatedly, causing a denial-of-service (DoS) condition by overwhelming the email infrastructure or recipients. The CVSS 3.1 base score of 7.5 reflects a high severity due to the vulnerability's network attack vector, lack of required privileges or user interaction, and its impact on availability. The vulnerability is classified under CWE-79, which typically relates to improper neutralization of input leading to cross-site scripting, but here it is linked to access control issues. Although no public exploits have been reported, the ease of exploitation and potential for service disruption make this a significant threat for organizations relying on BookStack for internal or external documentation. The absence of patches at the time of reporting necessitates immediate attention to mitigate risk.

The primary impact of CVE-2024-36676 is on the availability of services relying on BookStack's notification email system. Attackers can cause denial-of-service conditions by flooding notification channels, potentially disrupting communication workflows and administrative alerts. While confidentiality and integrity are not directly compromised, the ability to enumerate valid users can aid in further targeted attacks such as phishing or social engineering. Organizations with high dependency on BookStack for knowledge management may experience operational disruptions, loss of productivity, and increased support costs. Additionally, the public exposure of valid user accounts can weaken overall security posture by revealing internal user information. The vulnerability's network accessibility and lack of authentication requirements increase the risk of widespread exploitation, especially in environments where BookStack is exposed to the internet without adequate protections.

To mitigate CVE-2024-36676, organizations should upgrade BookStack to version 24.05.1 or later as soon as patches become available. Until then, administrators should restrict access to public-facing forms by implementing network-level controls such as IP whitelisting or VPN access to limit exposure. Rate limiting or CAPTCHA mechanisms on notification forms can reduce the risk of automated abuse. Monitoring email server logs for unusual spikes in notification traffic can help detect exploitation attempts early. Additionally, reviewing and tightening user enumeration protections, such as generic error messages that do not reveal user existence, will reduce information leakage. Employing web application firewalls (WAFs) with custom rules to block suspicious requests targeting notification endpoints can provide an additional layer of defense. Regular security audits and user awareness training on phishing risks related to user enumeration should complement technical controls.