CVE-2025-39534 identifies a reflected Cross-site Scripting (XSS) vulnerability in Somonator's Terms Dictionary software, versions up to and including 1.5.1. The vulnerability stems from improper neutralization of user-supplied input during the dynamic generation of web pages, allowing attackers to inject malicious JavaScript code that is reflected back to the user's browser. This reflected XSS does not require authentication (PR:N) but does require user interaction (UI:R), such as clicking a maliciously crafted URL. The vulnerability has a CVSS 3.1 base score of 7.1, indicating high severity, with an attack vector of network (AV:N), low attack complexity (AC:L), and scope changed (S:C), meaning the attack can affect resources beyond the vulnerable component. The impact includes partial loss of confidentiality, integrity, and availability, as attackers can execute scripts to hijack sessions, steal cookies, manipulate page content, or perform phishing attacks. Although no exploits are currently known in the wild, the vulnerability's characteristics make it a credible threat, especially in environments where Terms Dictionary is used to manage or display critical terminology data. The lack of available patches at the time of publication necessitates immediate mitigation efforts. The vulnerability was reserved in April 2025 and published in October 2025, indicating recent discovery and disclosure.

For European organizations, this vulnerability poses a significant risk to web applications that utilize Somonator Terms Dictionary, especially those exposed to external users or customers. Exploitation could lead to unauthorized access to sensitive information, session hijacking, and manipulation of displayed content, undermining user trust and potentially causing reputational damage. Organizations in sectors such as finance, healthcare, legal, and government, where terminology accuracy and confidentiality are critical, may face compliance and regulatory repercussions if exploited. The reflected XSS could also serve as an entry point for more complex attacks, including delivering malware or conducting social engineering campaigns. Given the network attack vector and low complexity, attackers can easily exploit this vulnerability remotely, increasing the threat surface. The scope change indicates that the impact may extend beyond the immediate application, potentially affecting integrated systems or services relying on Terms Dictionary data. The absence of known exploits currently provides a window for proactive defense but should not lead to complacency.

To mitigate CVE-2025-39534, European organizations should implement multiple layers of defense. First, apply any available patches or updates from Somonator promptly once released. In the absence of patches, implement strict input validation on all user-supplied data to ensure it conforms to expected formats and reject suspicious inputs. Employ comprehensive output encoding or escaping techniques when rendering user input in web pages to neutralize potentially malicious scripts. Deploy a robust Content Security Policy (CSP) that restricts the execution of inline scripts and limits sources of executable code. Conduct regular security testing, including automated scanning and manual penetration testing, to detect XSS vulnerabilities. Educate users and administrators about the risks of clicking unknown links and recognizing phishing attempts. Additionally, consider implementing Web Application Firewalls (WAFs) with rules tailored to detect and block reflected XSS payloads targeting Terms Dictionary endpoints. Monitor logs and alerts for unusual activity that may indicate exploitation attempts. Finally, review and harden the overall web application architecture to minimize attack surface exposure.