CVE-2024-39031 is a stored Cross-Site Scripting (XSS) vulnerability affecting Silverpeas Core versions up to 6.3.5, specifically in the Mes Agendas calendar module. In this system, users can create calendar events with fields such as "Titre" (Title) and "Description". The vulnerability arises because input sanitization is insufficient, allowing a standard user to inject malicious JavaScript code into these fields. The attacker can then invite other users, including administrators, to these events. When the invited user views their profile page, the stored malicious script executes automatically without requiring any click on the event, exploiting the trust relationship within the same domain. This stored XSS can lead to session hijacking, credential theft, or execution of arbitrary actions on behalf of the victim user. The attack requires the attacker to have at least standard user privileges and the victim to view their profile, but no further interaction is needed. The vulnerability is classified under CWE-79 (Improper Neutralization of Input During Web Page Generation). The CVSS 3.1 base score is 5.4, indicating medium severity, with an attack vector of network, low attack complexity, requiring privileges, and user interaction. No patches or known exploits are currently reported, but the risk remains significant due to the potential targeting of administrators and other privileged users.

The primary impact of CVE-2024-39031 is the compromise of user accounts, especially high-privilege accounts such as administrators, through stored XSS attacks. Successful exploitation can lead to session hijacking, theft of sensitive information, unauthorized actions performed on behalf of the victim, and potential lateral movement within the organization’s Silverpeas environment. This can undermine the confidentiality and integrity of organizational data and systems. Since the vulnerability allows attackers to target administrators by inviting them to malicious events, it increases the risk of privilege escalation and broader compromise. The availability impact is minimal as the vulnerability does not directly cause denial of service. Organizations using Silverpeas Core for collaboration and calendar management may face reputational damage, data breaches, and operational disruptions if exploited. The medium CVSS score reflects moderate ease of exploitation combined with significant potential impact on confidentiality and integrity.

To mitigate CVE-2024-39031, organizations should first check for any official patches or updates from Silverpeas and apply them promptly once available. In the absence of patches, implement strict input validation and output encoding on the "Titre" and "Description" fields to neutralize any injected scripts. Employ Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts in the application context. Limit the ability of standard users to invite administrators to events or implement additional verification steps before invitations are accepted. Monitor user activity logs for unusual event creation or invitation patterns. Educate users, especially administrators, to be cautious when viewing profile pages and consider temporarily restricting profile page access or disabling event invitations until the vulnerability is remediated. Conduct regular security assessments and penetration testing focused on XSS vulnerabilities. Finally, consider deploying Web Application Firewalls (WAFs) with rules to detect and block XSS payloads targeting Silverpeas.