CVE-2018-3814 in Craft
Summary
by MITRE
Craft CMS 2.6.3000 allows remote attackers to execute arbitrary PHP code by using the "Assets->Upload files" screen and then the "Replace it" option, because this allows a .jpg file to have embedded PHP code, and then be renamed to a .php extension.
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Analysis
by VulDB Data Team • 12/28/2019
This vulnerability in Craft CMS version 2.6.3000 represents a critical server-side code execution flaw that arises from improper file validation and handling within the asset management system. The issue manifests through the Assets->Upload files interface where users can replace existing files, creating a pathway for malicious actors to bypass security controls. The vulnerability stems from insufficient input sanitization and file extension validation mechanisms that fail to properly inspect file content regardless of its reported extension. Attackers can exploit this by uploading a maliciously crafted jpeg file containing embedded php code and then renaming it to have a .php extension, effectively circumventing the upload restrictions that should prevent execution of php scripts.
The technical exploitation occurs through a combination of file extension manipulation and content inspection bypass. When Craft CMS processes the file replacement operation, it does not perform comprehensive content validation to verify that a file with .php extension actually contains php code rather than being a legitimate image file. This creates a scenario where the system accepts the file based on its extension but fails to validate its actual content. The vulnerability operates at the application layer and can be classified under CWE-434 as "Unrestricted Upload of File with Dangerous Type" which directly relates to improper file type validation. The flaw is particularly dangerous because it allows attackers to execute arbitrary php commands on the server, potentially leading to complete system compromise.
The operational impact of this vulnerability extends beyond simple code execution to encompass full system compromise and data breach potential. An attacker who successfully exploits this vulnerability can gain unauthorized access to the server environment, potentially leading to data theft, system infiltration, or further lateral movement within the network infrastructure. The attack vector is particularly concerning because it leverages legitimate user functionality within the content management system, making it difficult to detect through standard network monitoring. This vulnerability can be exploited to upload backdoor scripts, modify existing files, or even establish persistent access to the compromised system, making it a significant threat to organizations relying on Craft CMS for their web presence.
Organizations should implement multiple layers of mitigation strategies to address this vulnerability effectively. Immediate patching of Craft CMS to version 2.6.3001 or later is essential as this release includes proper file validation and content inspection mechanisms. Additionally, administrators should implement strict file type validation policies that reject executable files regardless of their extension, combined with content-based file analysis that examines file headers and actual content rather than relying solely on extension-based checks. Network segmentation and access controls should be enforced to limit the impact of potential exploitation, while monitoring systems should be configured to detect unusual file upload patterns and unauthorized file modifications. The remediation approach should also include regular security audits and penetration testing to identify similar vulnerabilities in other applications and systems within the organization's infrastructure, following ATT&CK framework guidance for mitigating server-side request forgery and file upload vulnerabilities.