CVE-2024-5853 is a critical security vulnerability identified in the Sirv Image Optimizer, Resizer and CDN plugin for WordPress, affecting all versions up to 7.2.6. The root cause is a lack of proper file type validation in the AJAX handler sirv_upload_file_by_chanks, which processes file uploads. This missing validation allows authenticated users with Contributor-level permissions or higher to upload arbitrary files, including potentially malicious scripts, to the web server hosting the WordPress site. Because Contributors typically have limited privileges, this vulnerability significantly lowers the bar for attackers to achieve remote code execution (RCE) on the server, bypassing typical privilege restrictions. The vulnerability is classified under CWE-434 (Unrestricted Upload of File with Dangerous Type), which is a common vector for web application compromise. The CVSS v3.1 base score of 9.9 reflects the critical nature of this vulnerability, with an attack vector over the network, low complexity, privileges required at a low level, no user interaction needed, and a scope change indicating that the vulnerability affects components beyond the initially vulnerable plugin. Exploiting this flaw can lead to full system compromise, data theft, defacement, or use of the server as a pivot point for further attacks. No patches or official fixes were listed at the time of publication, and no known exploits in the wild have been reported yet, but the vulnerability's characteristics suggest imminent exploitation attempts.

The impact of CVE-2024-5853 is severe for organizations running WordPress sites with the vulnerable Sirv plugin. Successful exploitation can lead to remote code execution, allowing attackers to execute arbitrary commands on the server, potentially leading to full system compromise. This jeopardizes the confidentiality of sensitive data stored or processed by the website, the integrity of website content and backend systems, and the availability of the service due to possible defacement or denial-of-service conditions. Attackers could deploy web shells, malware, or ransomware, use the compromised server as a foothold for lateral movement within the network, or launch attacks against visitors. Given WordPress's widespread use globally, especially among small to medium businesses and content-heavy sites, the vulnerability poses a significant risk to a broad range of sectors including e-commerce, media, education, and government. The requirement for only Contributor-level access means that even users with relatively low privileges can exploit this flaw, increasing the risk from insider threats or compromised user accounts.

To mitigate CVE-2024-5853, organizations should immediately update the Sirv Image Optimizer, Resizer and CDN plugin to a patched version once available. Until a patch is released, administrators should consider disabling or removing the plugin to eliminate the attack surface. Implement strict access controls and review user roles to ensure that only trusted users have Contributor-level or higher permissions. Employ web application firewalls (WAFs) with rules designed to detect and block suspicious file upload attempts targeting the sirv_upload_file_by_chanks AJAX endpoint. Monitor server logs and WordPress activity for unusual file uploads or execution patterns. Additionally, harden the server by restricting execution permissions in upload directories and isolating the web server environment to limit the impact of potential compromises. Regularly back up website data and configurations to enable rapid recovery in case of an incident. Finally, educate site administrators and users about the risks of granting elevated permissions and the importance of applying security updates promptly.