CVE-2011-2745 in Chyrp
Summary
by MITRE
upload_handler.php in the swfupload extension in Chyrp 2.0 and earlier relies on client-side JavaScript code to restrict the file extensions of uploaded files, which allows remote authenticated users to upload a .php file, and consequently execute arbitrary PHP code, via a write_post action to the default URI under admin/.
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Analysis
by VulDB Data Team • 12/08/2024
The vulnerability described in CVE-2011-2745 affects the swfupload extension within Chyrp 2.0 and earlier versions, representing a critical security flaw that undermines the application's file upload validation mechanisms. This issue stems from a fundamental design weakness where the system delegates file extension validation to client-side JavaScript rather than implementing robust server-side verification. The vulnerability specifically targets the upload_handler.php component that processes file uploads through the swfupload functionality, creating an exploitable path for authenticated attackers to bypass intended security restrictions.
The technical implementation of this vulnerability exploits the trust placed in client-side validation mechanisms, which is a well-documented weakness categorized under CWE-693 Protection Mechanism Failure. The flaw occurs because the system relies entirely on client-side JavaScript to enforce file type restrictions, allowing malicious users to modify the JavaScript code or directly submit requests to bypass these controls. When an authenticated user performs a write_post action through the admin/ URI, the system processes the upload without proper server-side validation of the file extension, enabling the upload of malicious PHP files that can execute arbitrary code on the server.
This vulnerability presents significant operational impact as it allows authenticated attackers to escalate their privileges and gain full control over the affected system. The ability to upload PHP files creates a persistent backdoor that can be used for data exfiltration, system compromise, or further network infiltration. The attack vector requires only authentication access to the system, which is often easier to obtain than attempting to exploit unauthenticated vulnerabilities. This makes the vulnerability particularly dangerous in environments where administrative credentials might be compromised through social engineering, weak password policies, or other attack vectors.
The exploitation of this vulnerability aligns with several tactics described in the MITRE ATT&CK framework, particularly those related to privilege escalation and persistence mechanisms. Attackers can leverage this vulnerability to establish a foothold within the system and maintain access over time. The recommended mitigations include implementing robust server-side file extension validation, enforcing strict content type checking, and removing or disabling the swfupload extension until proper security controls are implemented. Additionally, organizations should ensure that all file upload mechanisms include multiple layers of validation, including server-side checks that cannot be bypassed by client-side modifications. The vulnerability underscores the critical importance of defense in depth principles and the necessity of not relying solely on client-side security controls for protecting critical system functions.