CVE-2025-57890 is a medium-severity Stored Cross-Site Scripting (XSS) vulnerability classified under CWE-79, affecting the Pierre Lannoy Sessions product up to version 3.2.0. The vulnerability arises due to improper neutralization of input during web page generation, allowing malicious actors to inject and store arbitrary scripts within the application. When other users access the affected pages, these scripts execute in their browsers, potentially leading to session hijacking, credential theft, or unauthorized actions performed on behalf of the victim. The CVSS 3.1 base score of 5.9 reflects a network attack vector with low attack complexity but requiring high privileges and user interaction. The scope is changed, indicating that the vulnerability affects components beyond the initially vulnerable module. Confidentiality, integrity, and availability impacts are all rated low but present. No known exploits are currently reported in the wild, and no patches have been linked yet. The vulnerability requires an authenticated user to inject the malicious payload and for another user to interact with the compromised content, which limits the ease of exploitation but does not eliminate risk, especially in environments with multiple users or shared sessions.

For European organizations using Pierre Lannoy Sessions, this vulnerability poses a risk of unauthorized access to sensitive session data and potential compromise of user accounts. Stored XSS can facilitate lateral movement within internal networks, data exfiltration, and manipulation of session states. Organizations in sectors such as finance, healthcare, and government, which often handle sensitive personal and operational data, could face regulatory repercussions under GDPR if user data confidentiality is breached. The requirement for authenticated access reduces the risk from external attackers but increases the threat from insider threats or compromised accounts. Additionally, the vulnerability could be leveraged in targeted phishing campaigns or social engineering attacks to escalate privileges or disrupt services. The lack of available patches necessitates immediate attention to mitigate exposure, especially for organizations with high user concurrency or public-facing session management.

European organizations should implement strict input validation and output encoding on all user-supplied data within the Sessions application to prevent script injection. Employ Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts. Conduct thorough code reviews focusing on areas where user input is reflected in web pages. Limit user privileges to the minimum necessary to reduce the risk of malicious payload injection. Monitor logs for unusual user activity indicative of attempted XSS exploitation. Until an official patch is released, consider deploying Web Application Firewalls (WAFs) with rules tailored to detect and block XSS payloads targeting Sessions. Educate users about the risks of clicking on suspicious links or interacting with untrusted content within the application. Finally, maintain an incident response plan to quickly address any exploitation attempts.