CVE-2018-14840 in Subrion CMS
Summary
by MITRE
uploads/.htaccess in Subrion CMS 4.2.1 allows XSS because it does not block .html file uploads (but does block, for example, .htm file uploads).
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 08/04/2025
The vulnerability identified as CVE-2018-14840 resides within the file upload handling mechanism of Subrion CMS version 4.2.1, specifically within the uploads/.htaccess configuration file. This issue represents a classic security misconfiguration that enables cross-site scripting attacks through improper file type validation. The flaw manifests when the system permits .html file uploads while simultaneously blocking .htm file uploads, creating an exploitable gap in the security controls that should enforce consistent file type restrictions across all potentially dangerous file extensions.
The technical implementation of this vulnerability stems from inconsistent validation logic within the content management system's upload filtering mechanism. When a user uploads an .html file, the system fails to properly sanitize or reject this file type despite the presence of security measures that would normally block similar files with different extensions. This inconsistency creates a pathway for malicious actors to upload malicious html files that contain embedded javascript code, which can then be executed in the context of other users' browsers when the files are accessed. The vulnerability specifically targets the .htaccess configuration file which controls how uploaded files are handled and interpreted by the web server, making it a critical point of failure in the application's security architecture.
The operational impact of this vulnerability extends beyond simple cross-site scripting to potentially enable more sophisticated attacks including session hijacking, credential theft, and the delivery of malicious payloads to unsuspecting users. When an attacker successfully uploads a malicious html file, they can leverage the stored XSS vector to execute arbitrary javascript code in the victim's browser, potentially stealing session cookies, redirecting users to phishing sites, or performing actions on behalf of authenticated users. This vulnerability particularly affects web applications that rely on user-uploaded content and demonstrates the critical importance of maintaining consistent security policies across all file type validations.
The root cause of this vulnerability aligns with CWE-20, which describes insecure input handling where applications fail to properly validate or sanitize user-supplied data. Additionally, this flaw relates to ATT&CK technique T1059.001 for command and scripting interpreter execution, as attackers can leverage the uploaded html files to execute malicious scripts. The inconsistency in file extension blocking also reflects poor input validation practices that should be addressed through comprehensive security testing and proper implementation of allowlists for file types. Organizations utilizing Subrion CMS should immediately implement proper file type validation, ensure consistent extension handling, and consider implementing additional security measures such as content security policies and proper file access controls to mitigate the risk of exploitation.
The remediation approach should focus on implementing a comprehensive file type validation system that does not rely on simple extension matching but instead employs multiple verification methods including MIME type checking, file content analysis, and proper configuration of the .htaccess file to prevent execution of uploaded files. Security teams should also conduct thorough penetration testing to identify similar inconsistencies in other parts of the application and ensure that all file upload mechanisms follow consistent security policies. The vulnerability serves as a reminder of the critical importance of maintaining security controls across all application components and the necessity of regular security assessments to identify and remediate such configuration flaws before they can be exploited by malicious actors.