CVE-2021-24693 in Simple Download Monitor Plugin
Summary
by MITRE • 11/08/2021
The Simple Download Monitor WordPress plugin before 3.9.5 does not escape the "File Thumbnail" post meta before outputting it in some pages, which could allow users with a role as low as Contributor to perform Stored Cross-Site Scripting attacks. Given the that XSS is triggered even when the Download is in a review state, contributor could make JavaScript code execute in a context of a reviewer such as admin and make them create a rogue admin account, or install a malicious plugin
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Analysis
by VulDB Data Team • 11/11/2021
The CVE-2021-24693 vulnerability resides within the Simple Download Monitor WordPress plugin, affecting versions prior to 3.9.5 and represents a critical stored cross-site scripting flaw that undermines the security posture of WordPress installations. This vulnerability specifically targets the "File Thumbnail" post meta field, which fails to undergo proper output escaping before being rendered on various pages within the plugin's interface. The flaw is particularly concerning because it operates with minimal privilege requirements, allowing users holding the Contributor role to execute malicious scripts, thereby bypassing typical security boundaries that should protect administrators and other elevated users from such attacks.
The technical implementation of this vulnerability stems from inadequate input sanitization within the plugin's codebase where the "File Thumbnail" metadata is directly incorporated into HTML output without proper HTML entity encoding or context-appropriate escaping mechanisms. This oversight creates a persistent XSS vector that remains active even when downloads are in a review state, meaning that malicious payloads can be executed immediately upon page load regardless of the content's approval status. The vulnerability's exploitation potential is amplified by its ability to target administrators who are reviewing content, as these privileged users are more likely to interact with the malicious code, making the attack surface particularly dangerous in environments where contributors might have access to sensitive administrative functions.
The operational impact of this vulnerability extends beyond simple script execution, as it provides attackers with the capability to escalate privileges and compromise entire WordPress installations. When a reviewer or administrator interacts with a maliciously crafted download entry, they could inadvertently execute JavaScript that creates rogue administrator accounts, installs malicious plugins, or modifies existing site configurations. This scenario aligns with attack patterns documented in the MITRE ATT&CK framework under the T1059.001 technique for command and scripting interpreter, where adversaries leverage XSS to establish persistent access. The vulnerability also maps to CWE-79 which describes cross-site scripting flaws, and specifically demonstrates how insufficient output escaping can lead to privilege escalation through malicious content injection.
Organizations should implement immediate mitigations including updating to Simple Download Monitor version 3.9.5 or later, which contains the necessary output escaping fixes for the affected meta field. Additionally, administrators should consider implementing Content Security Policy headers to limit the execution of inline scripts and reduce the impact of potential XSS exploitation. Network monitoring should be enhanced to detect suspicious JavaScript payloads within download metadata, and access controls should be reviewed to ensure that contributor-level users cannot upload content that might be rendered to administrators. The vulnerability also underscores the importance of proper input validation and output escaping practices as outlined in the OWASP Top Ten security principles, particularly focusing on the prevention of XSS attacks through consistent sanitization of user-supplied data before rendering in web contexts.