CVE-2025-39534 is a reflected Cross-site Scripting (XSS) vulnerability identified in Somonator's Terms Dictionary software, versions up to and including 1.5.1. The vulnerability stems from improper neutralization of input during web page generation, which allows an attacker to inject malicious JavaScript code into web pages viewed by other users. Specifically, the application fails to adequately sanitize or encode user-supplied input before including it in dynamically generated web content, leading to the execution of arbitrary scripts in the context of the victim's browser. This can be exploited by crafting a malicious URL or form input that, when clicked or submitted by a user, triggers the execution of attacker-controlled scripts. The CVSS v3.1 base score is 7.1, reflecting a high severity due to the network attack vector (AV:N), low attack complexity (AC:L), no privileges required (PR:N), but requiring user interaction (UI:R). The scope is changed (S:C), indicating that exploitation can affect resources beyond the vulnerable component. The impact metrics show low confidentiality, integrity, and availability impacts individually, but combined they can lead to significant security breaches such as session hijacking, theft of sensitive data, or defacement of web content. No known exploits have been reported in the wild yet, but the public disclosure increases the risk of exploitation. The vulnerability affects all deployments of Terms Dictionary up to version 1.5.1, with no patches currently linked, indicating that organizations must monitor vendor communications for updates. The vulnerability is typical of reflected XSS issues, which are among the most common web application security problems and can be leveraged in phishing campaigns or to bypass access controls.

For European organizations, this vulnerability poses a significant risk to web applications that incorporate Somonator's Terms Dictionary, especially those exposed to external users or customers. Successful exploitation can lead to unauthorized disclosure of sensitive information, including session tokens or personal data, potentially violating GDPR requirements. Integrity of displayed content can be compromised, damaging organizational reputation and trust. Availability impacts, while typically limited in reflected XSS, can occur if attackers use the vulnerability to inject disruptive scripts. The risk is heightened in sectors with stringent data protection and compliance obligations, such as finance, healthcare, and government. Additionally, the vulnerability could be used as a foothold for further attacks, including phishing or lateral movement within networks. The lack of known exploits in the wild currently provides a window for proactive defense, but the public disclosure means attackers may develop exploits soon. Organizations relying on Terms Dictionary should assess exposure, especially if the product is integrated into customer-facing portals or internal tools accessible via browsers.

Organizations should immediately inventory their use of Somonator Terms Dictionary and determine if affected versions (<=1.5.1) are in use. They should monitor Somonator's official channels for patches or updates addressing CVE-2025-39534 and apply them promptly once available. In the interim, implement strict input validation and output encoding on all user-supplied data to prevent script injection. Employ Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts in browsers. Web Application Firewalls (WAFs) can be configured to detect and block typical reflected XSS attack patterns targeting this product. Educate users to be cautious with unsolicited links and emails to reduce the risk of social engineering exploitation. Conduct security testing and code reviews focusing on input handling in the affected application components. If possible, isolate or restrict access to the vulnerable application to trusted users until remediation is complete. Logging and monitoring should be enhanced to detect suspicious activities indicative of attempted exploitation.