CVE-2025-61505 affects e107 CMS versions through 2.3.3 and involves insecure deserialization in the install.php script. Specifically, the vulnerability is in the handling of the previous_steps POST parameter, which is base64-decoded and then unserialized without any validation or sanitization. This unsafe deserialization can be exploited by attackers who craft malicious serialized PHP objects that, when unserialized, trigger PHP object injection. Depending on the available PHP object gadgets within the e107 codebase, this can lead to remote code execution (RCE), arbitrary file operations such as reading or writing files, or denial of service by causing application crashes or resource exhaustion. The vulnerability does not require authentication or user interaction and can be exploited remotely over the network, increasing its risk profile. The CVSS 3.1 base score is 6.5, indicating a medium severity with low impact on availability but some confidentiality and integrity risks. No patches or exploit code are currently publicly available, and no known active exploitation has been reported. However, the presence of this vulnerability in a widely used CMS component like install.php, which is often accessible during setup or upgrade phases, makes it a significant concern for administrators. The root cause is the use of PHP's unserialize function on untrusted input, a well-known insecure practice categorized under CWE-502 (Deserialization of Untrusted Data).

For European organizations using e107 CMS, this vulnerability poses a risk of unauthorized remote code execution, which could lead to full system compromise, data breaches, or service disruption. Attackers exploiting this flaw could execute arbitrary commands on web servers, potentially gaining access to sensitive data or pivoting within the network. The arbitrary file operation capability could allow attackers to modify or delete critical files, impacting data integrity and availability. Denial of service attacks could disrupt business operations, especially for organizations relying on e107 CMS for public-facing websites or internal portals. Given the network-exploitable nature and lack of authentication requirements, the vulnerability could be leveraged by attackers from anywhere, increasing the threat surface. The impact is particularly critical for sectors with strict data protection regulations such as finance, healthcare, and government within Europe, where breaches could result in regulatory penalties and reputational damage.

European organizations should immediately audit their use of e107 CMS and identify any instances running version 2.3.3 or earlier. Since no official patches are currently available, administrators should consider the following mitigations: 1) Restrict access to the install.php script by IP whitelisting or web server configuration to prevent unauthorized access. 2) Disable or remove the install.php script entirely on production systems after installation or upgrade to prevent exploitation. 3) Implement web application firewall (WAF) rules to detect and block suspicious POST requests containing base64-encoded serialized data targeting previous_steps parameter. 4) Monitor web server logs for unusual requests or error patterns indicative of deserialization attempts. 5) If possible, update or patch the CMS to a version that addresses this vulnerability once available. 6) Conduct code reviews to identify and refactor any other unsafe unserialize calls in the application. 7) Employ runtime application self-protection (RASP) or endpoint detection and response (EDR) tools to detect anomalous behaviors resulting from exploitation attempts. These steps will reduce the attack surface and help detect or prevent exploitation until an official patch is released.