CVE-2016-5839 in WordPress
Summary
by MITRE
WordPress before 4.5.3 allows remote attackers to bypass the sanitize_file_name protection mechanism via unspecified vectors.
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Analysis
by VulDB Data Team • 05/08/2019
WordPress versions prior to 4.5.3 contained a critical vulnerability in the sanitize_file_name function that allowed remote attackers to bypass file name sanitization protections. This vulnerability originated from insufficient input validation and filtering mechanisms within the core WordPress file handling system, creating a pathway for malicious actors to manipulate file names during upload operations. The flaw specifically affected the sanitization process that was designed to prevent potentially dangerous characters and sequences from being included in file names, which could lead to various security implications including directory traversal attacks and arbitrary file upload scenarios.
The technical implementation of this vulnerability stemmed from the WordPress core code where file name sanitization was not consistently applied across all upload pathways. Attackers could exploit this weakness by crafting specially formatted file names that would pass the initial validation checks but still retain malicious elements when processed by the system. This particular flaw fell under the category of improper input validation as classified by CWE-20, where the system failed to properly validate or sanitize user-provided data before processing it. The vulnerability was particularly concerning because it operated at the core level of WordPress file handling, affecting all plugins and themes that relied on the standard upload mechanisms.
The operational impact of this vulnerability was significant for WordPress installations, as it could enable attackers to bypass security measures designed to prevent malicious file uploads. Remote attackers could potentially upload files with dangerous extensions or payloads that would be executed on the server, leading to complete system compromise. The vulnerability created opportunities for directory traversal attacks where malicious file names could be crafted to navigate to unintended directories, and it also allowed for the execution of arbitrary code through the upload of malicious files such as php shells or webshells. This weakness directly impacted the principle of least privilege and could result in privilege escalation scenarios where attackers could gain elevated system access.
Organizations running vulnerable WordPress installations faced substantial risk of exploitation, particularly those with public-facing websites or content management systems that allowed user uploads. The vulnerability was particularly dangerous in multi-user environments where different users had varying levels of access to the upload functionality. Security teams needed to implement immediate mitigations including updating to WordPress version 4.5.3 or later, which contained the necessary patches to properly sanitize file names across all upload paths. Additional defensive measures included implementing strict file type validation, restricting upload directories, and monitoring for unusual file name patterns. The ATT&CK framework categorizes this vulnerability under T1059 for command and scripting interpreter and T1190 for exploit public-facing application, highlighting the exploitation methods and attack vectors that could be leveraged by threat actors. Organizations should have also considered implementing web application firewalls and security monitoring solutions to detect and prevent exploitation attempts targeting this specific vulnerability.