CVE-2025-53858 is a cross-site scripting (XSS) vulnerability identified in the ChatLuck chat application developed by NEOJAPAN Inc., affecting versions V6.6 R2.0 and earlier. The vulnerability resides in the chat rooms feature, where insufficient input sanitization allows an attacker to inject malicious JavaScript code. When a user accesses a compromised chat room, the injected script executes within their browser context, potentially enabling theft of session cookies, credential theft, or manipulation of the user interface. The CVSS v3.0 base score is 5.4, indicating a medium severity level. The vector string (AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N) reveals that the attack can be launched remotely over the network with low attack complexity, requires privileges (likely authenticated user access), and user interaction (clicking or viewing the malicious message). The scope is changed (S:C), meaning the vulnerability affects resources beyond the initially vulnerable component, increasing risk. Confidentiality and integrity are impacted, but availability remains unaffected. No public exploits have been reported yet, but the vulnerability's presence in a communication tool used for collaboration raises concerns about potential phishing or session hijacking attacks. The lack of available patches at the time of publication necessitates immediate attention from administrators. The vulnerability was reserved on 2025-09-02 and published on 2025-10-16, indicating recent discovery and disclosure.

For European organizations, the exploitation of this XSS vulnerability in ChatLuck could lead to unauthorized access to sensitive communications, session hijacking, and potential lateral movement within corporate networks. Since ChatLuck is a collaboration tool, attackers could leverage this vulnerability to impersonate users, steal confidential information, or distribute malware through malicious scripts. The medium severity suggests a moderate risk, but the impact on confidentiality and integrity could be significant in sectors handling sensitive data such as finance, healthcare, and government. The requirement for user interaction and some privilege level reduces the likelihood of widespread automated exploitation but does not eliminate targeted attacks. Organizations relying heavily on ChatLuck for internal communications may face reputational damage and compliance risks if sensitive data is compromised. Additionally, the vulnerability could be exploited to bypass access controls or escalate privileges within the application context, further increasing risk.

European organizations should immediately audit their ChatLuck deployments to identify affected versions (V6.6 R2.0 and earlier). Until an official patch is released, administrators should implement strict input validation and sanitization at the application or web server level, potentially using web application firewalls (WAFs) configured to detect and block XSS payloads targeting chat room inputs. User awareness training should emphasize caution when interacting with unexpected or suspicious chat messages. Restricting chat room access to trusted users and limiting privileges can reduce exploitation risk. Monitoring logs for unusual script injection attempts or anomalous user behavior is critical. Organizations should also consider isolating ChatLuck instances from critical network segments to contain potential breaches. Once a vendor patch becomes available, prompt application of updates is essential. Additionally, implementing Content Security Policy (CSP) headers can help mitigate the impact of injected scripts by restricting script execution sources.