CVE-2021-27817 in ShopXO
Summary
by MITRE • 03/16/2021
A remote command execution vulnerability in shopxo 1.9.3 allows an attacker to upload malicious code generated by phar where the suffix is JPG, which is uploaded after modifying the phar suffix.
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Analysis
by VulDB Data Team • 04/01/2021
The vulnerability CVE-2021-27817 represents a critical remote command execution flaw in the ShopXO e-commerce platform version 1.9.3 that stems from improper file validation and handling mechanisms. This vulnerability specifically targets the file upload functionality where attackers can exploit a weakness in the content type verification process to bypass security controls. The flaw allows malicious actors to upload specially crafted files with .JPG extensions that actually contain malicious PHP code wrapped in a phar archive format, creating a sophisticated attack vector that leverages the trust placed in image file extensions.
The technical implementation of this vulnerability exploits the underlying PHP phar deserialization mechanism combined with inadequate file extension validation. When the system processes uploaded files, it fails to properly validate the actual file content against the declared file type, allowing attackers to manipulate the file suffix from .phar to .JPG while maintaining the malicious phar payload within the file. This technique relies on the fact that PHP's phar extension can process files with various extensions as long as the internal phar archive structure is intact, effectively bypassing traditional file extension filters and security checks.
From an operational impact perspective, this vulnerability creates a severe threat landscape for ShopXO users as it enables full remote code execution capabilities without requiring authentication. Attackers can leverage this flaw to execute arbitrary commands on the target server, potentially leading to complete system compromise, data exfiltration, and persistent access. The vulnerability's remote nature means that attackers can exploit it from anywhere on the internet, making it particularly dangerous for publicly accessible e-commerce platforms that handle sensitive customer data and financial transactions. The attack surface is further expanded due to the ease of exploitation and the high privileges that can be gained through successful command execution.
The vulnerability aligns with CWE-434 which describes insecure file upload vulnerabilities where applications accept files without proper validation of content type, file extension, or file structure. This flaw also maps to ATT&CK technique T1190 which covers exploit public-facing application, and T1059 which covers command and scripting interpreter. Organizations should implement immediate mitigations including strict file type validation, removal of phar extension handling capabilities, and comprehensive file content inspection. The recommended remediation involves updating to the patched version of ShopXO, implementing proper MIME type checking, and deploying Web Application Firewalls to detect and block malicious upload attempts. Additionally, organizations should conduct thorough security audits of their file upload mechanisms and implement principle of least privilege for file upload directories to minimize potential damage from successful exploitation attempts.