CVE-2023-53977 is a stored cross-site scripting vulnerability identified in myBB Forums version 1.8.26, specifically within the forum management system. The vulnerability arises due to improper neutralization of input during web page generation, allowing authenticated administrators to inject arbitrary JavaScript code into the forum title field when creating new forums via the 'Forums and Posts' > 'Forum Management' interface. When other users or administrators view the forum listing page, the injected script executes in their browsers, potentially leading to session hijacking, credential theft, or redirection to malicious websites. The attack vector requires administrator-level privileges to insert the payload, and user interaction is necessary to trigger the malicious script upon viewing the forum listing. The CVSS 4.0 base score of 5.1 reflects a medium severity, considering the network attack vector, low complexity, no need for authentication beyond administrator privileges, and partial impact on confidentiality and integrity. No known exploits have been reported in the wild, and no official patches have been linked at the time of publication. The vulnerability highlights the importance of proper input validation and output encoding in web applications, especially in administrative interfaces that can affect content viewed by multiple users.

For European organizations using myBB Forums 1.8.26, this vulnerability poses a risk of client-side attacks that can compromise user sessions and data confidentiality. Since exploitation requires administrator access, the threat is primarily internal or from compromised administrator accounts. Successful exploitation can lead to unauthorized actions performed in the context of affected users, including theft of authentication tokens or redirection to phishing sites, potentially damaging organizational reputation and user trust. Public-facing forums with multiple administrators increase the attack surface. The impact on availability is minimal, but integrity and confidentiality of user data and sessions can be compromised. Organizations in sectors with high regulatory requirements for data protection, such as finance, healthcare, and government, may face additional compliance risks if user data is exposed or manipulated.

1. Immediately restrict administrator access to trusted personnel and enforce strong authentication mechanisms, such as multi-factor authentication (MFA). 2. Implement strict input validation and output encoding on all user-supplied data fields, especially the forum title field in the management interface, to neutralize potentially malicious scripts. 3. Monitor forum titles and administrative inputs for suspicious or unexpected script tags or payloads. 4. Regularly audit administrator activities and log changes to forum configurations to detect unauthorized injections. 5. If possible, upgrade to a patched version of myBB Forums once available or apply community-provided patches addressing this vulnerability. 6. Educate administrators about the risks of inserting untrusted content and the importance of secure coding practices. 7. Consider deploying Content Security Policy (CSP) headers to limit the execution of unauthorized scripts in browsers accessing the forum. 8. Conduct regular security assessments and penetration testing focusing on administrative interfaces.