CSW Discovers Stored Cross-Site Scripting (XSS) Zero-Day Vulnerability in WordPress Plugin
Posted on Oct 6, 2021 | By Surojoy Gupta
A Cross-Site Scripting (XSS) attack is of major concern to the cybersecurity world, especially web applications because it can allow attackers to gain control of user’s accounts and steal their personally identifiable information, other than login credentials. CSW researchers found one such medium severity vulnerability recently in Zoho CRM Lead Magnet.
CSW researchers have discovered a Cross-Site Scripting (XSS) vulnerability in Zoho CRM Lead Magnet Version 126.96.36.199.
The discovered vulnerability targets the application's users and not the application itself, and uses the user’s application as the attack vehicle. The XSS payload executes whenever the user changes the form values or deletes a created form in Zoho CRM Lead Magnet Version 188.8.131.52.
Vulnerability at a Glance
|Product Name||Zoho CRM Lead Magnet Plugin|
|Affected Version||Version 184.108.40.206|
|CWE ID||CWE-79: Improper Neutralization of Input During Web Page Generation|
|CVSS Vector||6.1 (CVSS:3.1/AV:L/AC:L/PR:H/UI:R/S:U/C:H/I:H/A:L)|
Proof of Concept
The following vulnerability was detected in Zoho CRM Lead Magnet Version 220.127.116.11.
Issue: Stored Cross-Site Scripting
Steps to reproduce:
1. Log in to the WordPress application.
Note: A virtual host (wptest.com) was used to test the application locally.
2. Install the Zoho CRM Lead Magnet Plugin.
Figure 01: Zoho CRM Lead Magnet Version 18.104.22.168
3. Configure the Client ID and Secret Key.
4. Click the ‘Create New Form’ button, fill in the values, and then click the ‘Next’ button.
Figure 02: New form in Zoho CRM Plugin
5. Encode the payload <img src=x onerror=alert(document.cookie)> with a hexadecimal HTML encoder.
Figure 03: Encoding the Payload
6. Enter the encoded payload in the ‘Form Name’ field (formvalue parameter) to update the form. Then, click the arrow button near the ‘Create a New Form’ heading to go back to the previous page.
Figure 04: Entering Encoded XSS Payload in the ‘form Name’ Field
7. Click on the pencil icon to edit the created form.
Figure 05: Click on the Pencil Icon to Edit the Form
8. Change any form value, such as ‘Company’ or the ‘Last Name’.
Figure 06: Modifying Form Fields
Figure 07: Injected XSS Payload Executed Displaying An Alert Box With Contents of the User’s Cookies
9. The XSS payload is also executed when the user tries to delete the form.
Figure 08: XSS Payload Executed When the User Tries To Delete the Form
With cross-site scripting, an attacker can control a script executed in the victim's browser and then fully compromise that user. An XSS vulnerability enables attacks that are self-contained within the application. This means that an attacker does not need to find an external means of inducing the victim to make a request containing their exploit. Rather, the attacker can insert the exploit into the application and simply wait for users to encounter it.
A cross-site scripting attack results in the following:
- Cookie theft
- Disclosure of end-user files
- Installation of Trojan horse programs
- Redirection of the user to some other page or site
To fix this vulnerability, follow these steps:
Perform context-sensitive encoding of untrusted input before it is echoed back to a browser by using the encoding library.
Implement input validation for special characters on all variables reflected on the browser and stored in the database.
Implement client-side validation.
Figure 09: Default Cross-Site Scripting Mitigation Setting in the wp.config File Prevents Cross-site Scripting Attacks
August 26, 2021: Discovered in Zoho CRM Lead Magnet Version 22.214.171.124.
September 1, 2021: Reported to WordPress Team
September 2, 2021: Vendor Acknowledged
September 2, 2021: The vendor blocked the plugin
September 6, 2021: Zoho fixed the issue
September 7, 2021: Vendor reopened the plugin for download
September 7, 2021: CVE-2021-33849 is assigned by Cyber Security Works
Cyber Security Works Pvt. Ltd., Chennai
Keep up-to-date with the newly patched vulnerabilities.