The SP Project & Document Manager WordPress plugin before 4.24 allows any authenticated users, such as subscribers, to upload files. The plugin attempts to prevent PHP and other similar files that could be executed on the server from being uploaded by checking the file extension. It was discovered that on Windows servers, the security checks in place were insufficient, enabling bad actors to potentially upload backdoors on vulnerable sites.

References

• https://nvd.nist.gov/vuln/detail/CVE-2021-4225
• https://github.com/pang0lin/CVEproject/blob/main/wordpress_SP-Project_fileupload.md
• https://wpscan.com/vulnerability/bd1083d1-edcc-482e-a8a9-c8b6c8d417bd