CVE-2025-39502 is a high-severity reflected Cross-site Scripting (XSS) vulnerability affecting the GoodLayers Hostel product, versions up to 3.1.2. This vulnerability arises due to improper neutralization of user input during web page generation, classified under CWE-79. Specifically, the application fails to adequately sanitize or encode input parameters before reflecting them back in the web page content, allowing an attacker to inject malicious scripts. When a victim user interacts with a crafted URL or input containing malicious JavaScript code, the script executes in the context of the victim's browser. This can lead to theft of session cookies, user impersonation, defacement, or redirection to malicious sites. The CVSS 3.1 base score of 7.1 indicates a high impact, with the vector AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:L meaning the attack can be launched remotely over the network with low attack complexity, no privileges required, but user interaction is necessary. The scope is changed (S:C), indicating that the vulnerability affects resources beyond the vulnerable component itself. The impact on confidentiality, integrity, and availability is low to moderate but combined with scope change, it can affect other components or users. No known exploits are currently reported in the wild, and no patches have been linked yet. The vulnerability is significant because reflected XSS can be leveraged in phishing campaigns or combined with other vulnerabilities to escalate attacks.

For European organizations using GoodLayers Hostel, this vulnerability poses a risk of client-side attacks that can compromise user accounts, steal sensitive session information, or facilitate social engineering attacks. Hospitality and accommodation services, which often handle personal and payment data, could see reputational damage and regulatory consequences if exploited. The reflected XSS can be used to target customers or employees, potentially leading to unauthorized access or data leakage. Given the GDPR framework, any data breach resulting from exploitation could lead to significant fines and legal repercussions. Additionally, the scope change in the vulnerability suggests that the impact might extend beyond the immediate application, potentially affecting integrated systems or services. Organizations relying on this software for booking or customer management should be particularly cautious, as attackers could exploit this vulnerability to inject malicious scripts that compromise user trust and system integrity.

Immediate mitigation steps include implementing strict input validation and output encoding on all user-supplied data reflected in web pages. Organizations should apply Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts and reduce the impact of XSS attacks. Employing web application firewalls (WAFs) with rules to detect and block reflected XSS payloads can provide temporary protection until patches are available. It is critical to monitor for suspicious URL patterns or user reports of unusual behavior. Since no official patch is currently linked, organizations should engage with GoodLayers for updates and consider isolating or limiting access to vulnerable components. Security teams should conduct thorough code reviews and penetration testing focused on input handling and script injection vectors. User education about phishing and suspicious links can reduce the risk of successful exploitation. Finally, logging and alerting on anomalous web requests can help detect exploitation attempts early.