CVE-2025-55824 is an arbitrary file write vulnerability identified in ModStartCMS version 9.5.0. This vulnerability allows an unauthenticated attacker to write arbitrary files to the server hosting the CMS. By exploiting this flaw, attackers can upload malicious files, such as web shells or scripts, which can then be executed to perform unauthorized actions on the server. The vulnerability is classified under CWE-77, which relates to improper neutralization of special elements used in a command ('Command Injection'). The CVSS v3.1 base score is 6.5, indicating a medium severity level. The vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N) shows that the attack can be performed remotely over the network without any privileges or user interaction, affecting confidentiality and integrity but not availability. The vulnerability does not have any known exploits in the wild yet, and no official patches have been linked or published at this time. The lack of authentication requirement and the ability to write arbitrary files make this a significant risk, as it can lead to sensitive data exposure and potential further compromise of the server environment.

For European organizations using ModStartCMS 9.5.0, this vulnerability poses a considerable risk. The ability for an attacker to write arbitrary files and execute commands can lead to data breaches, including theft of sensitive customer or business data. It may also allow attackers to establish persistent access, pivot within the network, or disrupt business operations indirectly through data integrity compromise. Given that ModStartCMS is a content management system, websites and web applications running on this platform could be defaced, manipulated, or used as a launchpad for further attacks. This can damage organizational reputation, lead to regulatory non-compliance (e.g., GDPR violations due to data exposure), and incur financial losses. The medium CVSS score reflects that while the vulnerability is serious, it does not directly impact availability or require complex attack conditions, making it a moderate but urgent concern for affected entities.

Organizations should immediately verify if they are running ModStartCMS version 9.5.0 and prioritize upgrading to a patched version once available. In the absence of an official patch, temporary mitigations include restricting write permissions on directories accessible by the CMS to prevent unauthorized file uploads. Implementing web application firewalls (WAFs) with rules to detect and block suspicious file upload patterns or command injection attempts can reduce exposure. Regularly auditing server logs for unusual file creation or execution activities is recommended. Additionally, isolating the CMS environment using network segmentation can limit the impact of a successful exploit. Organizations should also enforce strict input validation and sanitization on any user inputs processed by the CMS to reduce injection risks. Finally, maintaining up-to-date backups and having an incident response plan tailored to web application compromises will aid in rapid recovery if exploitation occurs.