CVE-2022-39297 is a vulnerability classified under CWE-502, which involves the deserialization of untrusted data in the MelisCms component of the Melis Platform. MelisCms is a content management system that provides features such as templating, drag-and-drop plugins, SEO tools, and administrative functionalities. The vulnerability affects versions of melisplatform/melis-cms up to and including 5.0.0. The core issue arises from the system's unsafe handling of serialized data inputs, allowing attackers to supply crafted serialized objects that the application deserializes without proper validation or restriction. This leads to the execution of arbitrary PHP code on the affected system. Notably, exploitation of this vulnerability does not require any authentication or user interaction, making it highly accessible to remote attackers. The root cause was addressed in version 5.0.1 by implementing restrictions on the classes allowed during deserialization, effectively preventing malicious payloads from triggering code execution. Although there are no known exploits in the wild as of the published date, the nature of the vulnerability—remote code execution without authentication—makes it a critical risk if left unpatched. The vulnerability was publicly disclosed on October 12, 2022, and has been enriched by CISA, indicating recognition by cybersecurity authorities. The absence of a CVSS score requires an independent severity assessment based on the potential impact and exploitability factors.

For European organizations using MelisCms versions 5.0.0 or earlier, this vulnerability poses a significant risk. Successful exploitation could lead to full system compromise, allowing attackers to execute arbitrary PHP code remotely. This could result in unauthorized access to sensitive data, defacement of websites, disruption of services, or use of compromised servers as pivot points for further attacks within the network. Given that MelisCms is a CMS, organizations in sectors such as media, publishing, e-commerce, and public administration that rely on this platform for their web presence are particularly vulnerable. The lack of authentication requirement lowers the barrier for attackers, increasing the likelihood of automated scanning and exploitation attempts. Additionally, compromised CMS platforms can be leveraged to distribute malware or conduct phishing campaigns, amplifying the threat beyond the initial target. The impact on confidentiality, integrity, and availability is therefore high, with potential reputational damage and regulatory consequences under GDPR for data breaches. The absence of known exploits in the wild suggests that proactive patching can effectively mitigate risk before widespread exploitation occurs.

European organizations should immediately upgrade melisplatform/melis-cms to version 5.0.1 or later, where the vulnerability has been fixed by restricting allowed classes during deserialization. Beyond upgrading, organizations should implement the following specific measures: 1) Conduct a thorough inventory of all web applications to identify any instances of MelisCms and verify their versions. 2) Employ web application firewalls (WAFs) with custom rules to detect and block suspicious serialized payloads targeting deserialization endpoints. 3) Monitor web server and application logs for unusual POST requests or serialized data patterns indicative of exploitation attempts. 4) Apply strict input validation and sanitization on all user-supplied data, especially where deserialization occurs. 5) Implement network segmentation to limit the impact of a potential compromise of the CMS server. 6) Regularly backup CMS data and configurations to enable rapid recovery in case of compromise. 7) Educate development and security teams about secure coding practices related to serialization and deserialization to prevent similar vulnerabilities in custom code. These targeted actions, combined with patching, will reduce the attack surface and improve detection and response capabilities.