CVE-2021-24440 in Sign-up Sheets Plugin
Summary
by MITRE • 07/13/2021
The Sign-up Sheets WordPress plugin before 1.0.14 did not sanitise or escape some of its fields when creating a new sheet, allowing high privilege users to add JavaScript in them, leading to a Stored Cross-Site Scripting issue. The payloads will be triggered when viewing the 'All Sheets' page in the admin dashboard
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Analysis
by VulDB Data Team • 07/15/2021
The CVE-2021-24440 vulnerability affects the Sign-up Sheets WordPress plugin version 1.0.13 and earlier, representing a critical stored cross-site scripting flaw that exploits insufficient input sanitization mechanisms. This vulnerability specifically targets the plugin's sheet creation functionality where user inputs are not properly validated or escaped before being stored in the database and subsequently rendered on the admin dashboard interface. The flaw enables attackers with high privilege user accounts to inject malicious JavaScript code into plugin fields, which then executes whenever administrators view the 'All Sheets' page in the WordPress admin area. This represents a classic stored XSS attack vector where malicious payloads persist in the application's database and are delivered to unsuspecting users during routine administrative operations.
The technical implementation of this vulnerability stems from the plugin's failure to apply proper sanitization routines to user-supplied data during the sheet creation process. According to CWE-79, this vulnerability maps directly to Cross-Site Scripting flaws that occur when untrusted data is included in web pages without proper validation or escaping. The vulnerability's impact is amplified by the fact that it requires only high privilege user access, which is typically limited to administrators or editors within WordPress systems, making it particularly dangerous in environments where these roles are frequently used. The stored nature of the vulnerability means that once malicious code is injected, it will execute automatically every time the affected page is loaded, providing attackers with persistent access to the administrative interface.
The operational implications of this vulnerability extend beyond simple script execution, as it can enable attackers to escalate privileges, steal administrative sessions, or manipulate the plugin's functionality to compromise the entire WordPress installation. Attackers could potentially use this vulnerability to modify or delete sheets, alter user permissions, or even inject additional malicious code that could propagate to other parts of the WordPress system. The vulnerability's exploitation requires minimal technical skill since it leverages existing administrative privileges, making it an attractive target for threat actors seeking to gain unauthorized access to WordPress sites. According to ATT&CK framework, this vulnerability aligns with T1059.007 (Command and Scripting Interpreter: JavaScript) and T1566.002 (Phishing: Spearphishing Attachment) as it enables persistent script execution and can be used as part of broader attack chains targeting web applications. The vulnerability's presence in the admin dashboard context also makes it particularly effective for social engineering attacks where attackers can craft malicious payloads that appear legitimate to administrators.
Mitigation strategies for CVE-2021-24440 primarily focus on immediate plugin updates to version 1.0.14 or later, which contain the necessary sanitization fixes. Organizations should also implement additional security measures including regular plugin auditing, monitoring for suspicious administrative activities, and ensuring that only essential users have high privilege accounts. The vulnerability highlights the importance of input validation and output escaping practices as outlined in the OWASP Top Ten security principles, particularly the need for proper data sanitization at all entry points. Network-level monitoring and intrusion detection systems should be configured to detect unusual administrative activities that might indicate exploitation attempts. Additionally, implementing role-based access controls and limiting administrative privileges to only necessary personnel reduces the attack surface and minimizes the potential impact of such vulnerabilities in the event of compromise.