CVE-2025-57520 is a Cross Site Scripting (XSS) vulnerability identified in Decap CMS versions up to 3.8.3. The vulnerability arises because several input fields within the CMS—specifically body, tags, title, and description—do not properly sanitize user-supplied input before rendering it in the content preview pane. This improper input validation allows an attacker to inject arbitrary JavaScript code that executes whenever a user views the preview panel. The vulnerability affects multiple input vectors, increasing the attack surface. Notably, exploitation does not require any user interaction beyond simply viewing the affected content in the preview pane, which means that an attacker can trigger the malicious script execution without additional user actions such as clicking or submitting forms. The vulnerability is classified under CWE-79 (Improper Neutralization of Input During Web Page Generation), a common and well-understood category of XSS flaws. The CVSS v3.1 base score is 6.1, indicating a medium severity level. The vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N) shows that the attack can be performed remotely over the network with low attack complexity, requires no privileges, but does require user interaction (viewing the preview). The scope is changed, meaning the vulnerability affects components beyond the initially vulnerable component, and it impacts confidentiality and integrity but not availability. No known exploits are currently reported in the wild, and no patches have been linked yet. This vulnerability is significant because Decap CMS is used to manage website content, and successful exploitation could allow attackers to steal session tokens, perform actions on behalf of users, or deliver malicious payloads within the context of the CMS interface.

For European organizations using Decap CMS, this vulnerability poses a risk of client-side code injection leading to session hijacking, unauthorized actions, or data leakage within the CMS environment. Since the vulnerability executes in the context of the CMS preview pane, attackers could target content editors or administrators, potentially compromising sensitive content management workflows. This could lead to unauthorized content modifications, leakage of internal information, or pivoting to further attacks within the organization’s network. The medium severity score reflects that while the vulnerability does not directly impact system availability, it compromises confidentiality and integrity, which are critical for maintaining trust and operational security. European organizations in sectors such as media, publishing, education, and government that rely on Decap CMS for content management are particularly at risk. Additionally, the vulnerability could be leveraged in targeted phishing or social engineering campaigns to trick users into viewing malicious content previews, amplifying the risk. The lack of required privileges lowers the barrier for attackers, increasing the likelihood of exploitation if the vulnerability is not remediated promptly.

To mitigate CVE-2025-57520, European organizations should prioritize the following actions: 1) Apply patches or updates from Decap CMS as soon as they become available to address the input sanitization flaws. 2) In the absence of official patches, implement web application firewall (WAF) rules to detect and block suspicious script injection attempts targeting the vulnerable input fields (body, tags, title, description). 3) Restrict access to the CMS preview pane to trusted users only, minimizing exposure to untrusted or anonymous users. 4) Conduct thorough input validation and output encoding on all user-supplied content rendered in the preview pane, ideally using context-aware encoding libraries to neutralize script injection vectors. 5) Educate content editors and administrators about the risks of viewing untrusted content previews and encourage cautious behavior when handling content from unknown sources. 6) Monitor CMS logs and network traffic for unusual activity indicative of exploitation attempts. 7) Consider implementing Content Security Policy (CSP) headers to restrict the execution of inline scripts and reduce the impact of potential XSS payloads. These measures, combined, will reduce the attack surface and mitigate the risk until a full patch is deployed.