WordPress is an open publishing platform for the Web. Its possible for a file of a type other than a zip file to be submitted as a new plugin by an administrative user on the Plugins -> Add New -> Upload Plugin screen in WordPress. If FTP credentials are requested for installation (in order to move the file into place outside of the uploads directory) then the uploaded file remains temporary available in the Media Library despite it not being allowed. If the DISALLOW_FILE_EDIT constant is set to true on the site and FTP credentials are required when uploading a new theme or plugin, then this technically allows an RCE when the user would otherwise have no means of executing arbitrary PHP code. This issue only affects Administrator level users on single site installations, and Super Admin level users on Multisite installations where its otherwise expected that the user does not have permission to upload or execute arbitrary PHP code. Lower level users are not affected. Sites where the DISALLOW_FILE_MODS constant is set to true are not affected. Sites where an administrative user either does not need to enter FTP credentials or they have access to the valid FTP credentials, are not affected. The issue was fixed in WordPress 6.4.3 on January 30, 2024 and backported to versions 6.3.3, 6.2.4, 6.1.5, 6.0.7, 5.9.9, 5.8.9, 5.7.11, 5.6.13, 5.5.14, 5.4.15, 5.3.17, 5.2.20, 5.1.18, 5.0.21, 4.9.25, 2.8.24, 4.7.28, 4.6.28, 4.5.31, 4.4.32, 4.3.33, 4.2.37, and 4.1.40. A workaround is available. If the DISALLOW_FILE_MODS constant is defined as true then it will not be possible for any user to upload a plugin and therefore this issue will not be exploitable.
Weakness
The product allows the attacker to upload or transfer files of dangerous types that can be automatically processed within the product’s environment.
Potential Mitigations
- Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
- When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
- Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
- For example, limiting filenames to alphanumeric characters can help to restrict the introduction of unintended file extensions.
- Run the code in a “jail” or similar sandbox environment that enforces strict boundaries between the process and the operating system. This may effectively restrict which files can be accessed in a particular directory or which commands can be executed by the software.
- OS-level examples include the Unix chroot jail, AppArmor, and SELinux. In general, managed code may provide some protection. For example, java.io.FilePermission in the Java SecurityManager allows the software to specify restrictions on file operations.
- This may not be a feasible solution, and it only limits the impact to the operating system; the rest of the application may still be subject to compromise.
- Be careful to avoid CWE-243 and other weaknesses related to jails.
References