julienbrs/exploit-cve-2023-3460Exploit and analysis of CVE-2023-3460, a critical privilege escalation in the Ultimate Member WordPress plugin, with reproduction environment and mitigation guidance.
| CVE ID | CVSS Score | Discovered | Affected Plugin | Vulnerability Type |
|---|---|---|---|---|
| CVE-2023-3460 |  | 07/04/2023 | Ultimate Member | Unauthorized Admin Access |
This study focuses on CVE¹-2023-3460, a critical vulnerability affecting the "Ultimate Member" WordPress plugin, allowing unauthorized privilege escalation. This plugin is widely deployed and used for profile management on WordPress sites. This vulnerability poses a major risk because it allows an attacker to obtain administrator rights and therefore full control of the site. This is why this flaw was classified as critical and rated 9.1 on the CVSS scale by NIST².
CVE-2023-3460 exploits a flaw in the plugin's role and permission management. In WordPress, the WP_Capabilities³ function is used to manage user roles and permissions. This function allows administrators to define specific capabilities for each user role. However, improper use of this function can lead to privilege escalation vulnerabilities.
In the case of Ultimate Member, the vulnerability allows an attacker to bypass WP capability checks and gain administrator-level access to the site. The plugin operates by using a predefined list of user metadata keys that should not be manipulated by users. However, this security approach, based on blocklists, is often insufficient because it leaves room for bypasses.
WordPress manages user roles and permissions through a structure called wp_capabilities. This structure is a serialized representation of the different roles and permissions granted to users. For example, an administrator will have a different set of capabilities than an editor or a contributor. These capabilities are stored in the WordPress database as serialized arrays in the wp_usermeta table.
The CVE-2023-3460 flaw originates from Ultimate Member's implementation of role and permission management. The plugin operates by using a predefined list of user metadata keys that users should not manipulate. This list is used to check whether users attempt to save these keys when creating an account. This approach is a common security anti-pattern, where blocking known harmful inputs (blocklists) may seem intuitive, but proves more complex than expected and often leaves room for security bypasses.
Here, Ultimate Member uses insufficient verification of metadata submitted during user registration. The plugin uses a function called is_metakey_banned to check whether the metadata submitted by the user is allowed. This function checks whether the submitted metadata appears in the list of banned metadata. If so, the function returns true and user registration is blocked. Otherwise, the function returns false and user registration is allowed.
However, WordPress accepts certain accented characters as default characters. If a user submits metadata with accented characters, the is_metakey_banned function will not detect them and user registration will be allowed.
The Ultimate Member plugin is widely used in various environments, ranging from small personal blogs to large e-commerce sites. No specific assumption can be made about the IT security skills of end users or site administrators.
Servers hosting WordPress sites are generally located in secure data centers. For personal sites, physical security depends on the individual user's environment.
It is assumed that the Ultimate Member plugin is installed and configured correctly according to the official instructions. The WordPress site is assumed to be kept up to date, with basic security measures in place.
7.5 Security functions
As an administrator, here are concrete measures that can be taken to mitigate the risks associated with this vulnerability.
User Input Validation: Implement server-side validations to check all user inputs, especially those that modify metadata such as wp_capabilities. Use regular expressions or validation lists (whitelists) rather than blocklists to control inputs.
CAPTCHA and Rate Limits: Integrate CAPTCHAs and rate limits on registration forms to prevent automated attacks. Client-Side Checks: Although client-side validations are not sufficient on their own, they can help prevent automated attacks and improve the user experience.
Log Monitoring: Set up a log monitoring system to detect any suspicious changes to user roles or metadata injection attempts. This can be done using log analysis tools.
Web Application Firewall (WAF): Configure a WAF⁴ to block known and unknown attacks, including malicious code injection attacks. Intrusion Detection/Prevention Systems (IDS/IPS)⁵: Implement an IDS/IPS to detect attempts to exploit the vulnerability.
User Role Review: Regularly review the roles assigned to users to detect any abnormal privilege escalation. Permission Restriction: Limit the permissions granted by default to new users and require administrative validation for assigning elevated roles, following the principle of least privilege. See details on this principle here.
Rapid Application of Updates: Perform regular security updates for plugins and WordPress itself.
Train developers on the security best practices mentioned above, and raise awareness of the risks/impacts of poor implementation.
A Makefile is available to help you launch the exploitation of the flaw. You can use it as follows:
make up to launch WordPress with all necessary installations. After a waiting period, it will start a WordPress server, configure it, and install version 2.6.5 of the Ultimate Member plugin.
You will then be able to log into WordPress on the Login page with the credentials admin:password. By going to the Users tab, you will see
that only the admin user is present.
Note: if you have docker-compose and not docker compose, you can modify the Makefile accordingly (variable DOCKER_COMPOSE= docker-compose).
Then, you can launch the exploitation of the flaw:
make exploit
You will then be able to log into WordPress on Login with the credentials provided by the exploit and observe in the Users tab that a new user has been created with the Administrator role.
make down to stop the WordPress server and delete the data.
make exploit runs the exploit.py script. This script acts in several steps:
Technical Details of the Exploit1. Vulnerability Check: Before proceeding with the exploitation, the script checks whether the version of the Ultimate Member plugin installed on the target site is vulnerable, i.e., lower than version 2.6.7.
2. Retrieving the Security Nonce: The script retrieves a security nonce³ from the target site's registration page. This nonce is required for the registration request to be accepted by WordPress. The nonce is retrieved by parsing the HTML code of the registration page.
3. Exploiting the Vulnerability: The script then submits a POST request to the registration page, including a manipulated parameter (wp_càpabilities[administrator]=1). This parameter uses an accented character (à) to bypass the plugin's security controls and incorrectly serialize the data, thereby assigning the administrator role to the newly created user.
4. Exploit Confirmation: After sending the request, the script checks whether the operation succeeded by parsing the server's response.
| Threats | A1 (User data confidentiality) | A2 (Website integrity) | A3 (Ultimate Member plugin integrity) |
|---|
| T1 Unauthorized access | X | X | X |
| T2 Malicious code injection | X | X | |
| T3 Data leakage | X | ||
| T4 Reputation damage | X |
| Name | Link |
|---|
| NIST CVE-2023-3460 | https://nvd.nist.gov/vuln/detail/CVE-2023-3460 |
| Ultimate Member Github | https://github.com/ultimatemember/ultimatemember |
| Package version used for exploitation 2.6.5 | https://wordpress.org/plugins/ultimate-member/advanced/ |
| Patch of the exploit | https://github.com/ultimatemember/ultimatemember/commit/fae47c6065ce07e9a8b44501002fa5b4f16d2456 |
| Review of the exploit | https://thesecmaster.com/how-to-fix-cve-2023-3460-a-privilege-escalation-vulnerability-in-ultimate-member-wordpress-plugin/ |
| OWASP Top 10 Application Security Risks | https://owasp.org/www-project-top-ten/ |