CVE-2020-4047 in WordPress
Summary
by MITRE
In affected versions of WordPress, authenticated users with upload permissions (like authors) are able to inject JavaScript into some media file attachment pages in a certain way. This can lead to script execution in the context of a higher privileged user when the file is viewed by them. This has been patched in version 5.4.2, along with all the previously affected versions via a minor release (5.3.4, 5.2.7, 5.1.6, 5.0.10, 4.9.15, 4.8.14, 4.7.18, 4.6.19, 4.5.22, 4.4.23, 4.3.24, 4.2.28, 4.1.31, 4.0.31, 3.9.32, 3.8.34, 3.7.34).
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 10/24/2020
This vulnerability exists within WordPress core software where authenticated users possessing upload privileges can exploit a flaw in media file attachment handling to inject malicious javascript code. The issue specifically affects users with roles such as authors who have the capability to upload files but typically lack administrative privileges. The vulnerability stems from insufficient input validation and output encoding when processing media file metadata, creating a cross-site scripting attack vector that can be leveraged by malicious actors with limited permissions. The flaw allows attackers to inject javascript code into media file attachment pages, which then executes when viewed by other users, including those with higher privileges such as administrators or editors. This represents a privilege escalation vulnerability where a lower-privileged user can potentially compromise higher-privileged accounts through malicious file uploads.
The technical implementation of this vulnerability involves the manipulation of media file metadata or content during the upload process, specifically targeting how WordPress handles file attachment pages. When an attacker uploads a media file and injects javascript code into the file's metadata or content, the system fails to properly sanitize or encode this input before rendering it on the attachment page. This allows the injected javascript to execute in the browser context of any user who views the affected file, regardless of their permission level. The vulnerability is particularly dangerous because it leverages the trust relationship between users and the system, enabling attackers to execute code in the context of higher-privileged users who view the malicious files. This type of vulnerability aligns with CWE-79 - Improper Neutralization of Input During Web Page Generation, which addresses the failure to properly encode or escape user-controllable data before including it in web page output. The attack pattern follows the typical exploitation sequence where a user with limited privileges crafts malicious content that gets executed when viewed by a more privileged user, creating a persistent threat vector.
The operational impact of this vulnerability extends beyond simple script execution, as it can enable attackers to perform a wide range of malicious activities including session hijacking, data exfiltration, and further privilege escalation. An attacker could potentially steal administrator sessions, modify content, delete files, or even install backdoors on the affected WordPress installation. The vulnerability affects all versions of WordPress from 3.7 through 5.4, making it a significant concern for organizations running older versions of the platform. The attack requires minimal privileges, as authors and other users with upload capabilities can exploit this issue, making it particularly dangerous in environments where multiple users have upload permissions. The impact is amplified by the fact that many WordPress installations have authors or contributors with upload privileges, creating numerous potential attack vectors across different user roles. This vulnerability also aligns with ATT&CK technique T1059.007 - Command and Scripting Interpreter: JavaScript, as it enables execution of malicious javascript code within the browser context of target users.
The remediation for this vulnerability was implemented through WordPress version 5.4.2 and subsequent patch releases for all previously affected versions. The fix involves implementing proper input sanitization and output encoding mechanisms that prevent javascript code from being executed when media files are displayed on attachment pages. This patch addresses the core issue by ensuring that user-provided content in media file metadata is properly escaped or filtered before being rendered in web pages. Organizations should immediately upgrade to WordPress version 5.4.2 or later to protect against this vulnerability, as well as apply the relevant patches for older versions. Additionally, administrators should review user permissions and consider restricting upload capabilities for users who do not require them, particularly in environments where multiple users have access to the system. The patch demonstrates the importance of proper input validation and output encoding in preventing cross-site scripting attacks, aligning with security best practices outlined in both CWE and OWASP Top Ten security standards. Organizations should also implement additional monitoring to detect unusual file upload activities and consider implementing content security policies to further mitigate the risk of script execution attacks.