CVE-2024-12427 is a missing authorization vulnerability (CWE-862) in the Multi Step Form plugin for WordPress developed by mondula2016. The flaw exists because the plugin fails to perform a capability check on the AJAX action fw_upload_file, which handles file uploads. This omission allows unauthenticated attackers to invoke this action and upload files of limited types, primarily images, without any permission validation. The vulnerability affects all plugin versions up to and including 1.7.23. The attack vector is network-based and requires no privileges or user interaction, making it relatively easy to exploit. Although the uploaded files are restricted to certain types, this can still be abused to alter site content or facilitate further attacks such as phishing, defacement, or social engineering. The CVSS v3.1 base score is 5.3 (medium severity), reflecting the lack of confidentiality or availability impact but acknowledging the integrity impact due to unauthorized file uploads. No patches or official fixes are currently linked, and no known exploits have been reported in the wild. The vulnerability is particularly relevant for WordPress sites using this plugin, which is a popular form-building tool, thus potentially affecting a broad range of websites globally.

The primary impact of CVE-2024-12427 is unauthorized integrity modification through limited file uploads. Attackers can upload image files without authentication, which could be used to deface websites, insert misleading content, or host malicious images for phishing or social engineering campaigns. While the vulnerability does not allow direct code execution or access to sensitive data, the ability to upload files without authorization undermines the trustworthiness of affected websites and can damage organizational reputation. In some cases, attackers might chain this vulnerability with other flaws to escalate privileges or execute further attacks. Organizations relying on the Multi Step Form plugin face risks of website defacement, brand damage, and potential indirect compromise. The ease of exploitation and lack of authentication requirements increase the likelihood of opportunistic attacks, especially on high-traffic or high-profile sites.

To mitigate CVE-2024-12427, organizations should immediately update the Multi Step Form plugin to a version that includes proper authorization checks once available. Until a patch is released, administrators can implement the following specific mitigations: 1) Disable or restrict access to the fw_upload_file AJAX action by modifying plugin code or using WordPress hooks to enforce capability checks. 2) Employ a web application firewall (WAF) to detect and block unauthorized AJAX requests targeting the vulnerable endpoint. 3) Restrict file upload directories with strict permissions and disable execution of uploaded files to prevent abuse. 4) Monitor web server logs for unusual upload activity or repeated requests to the fw_upload_file action. 5) Educate site administrators on the risks of unauthorized file uploads and encourage regular plugin updates. These targeted actions go beyond generic advice by focusing on the specific vulnerable component and attack vector.