Canshu PHP Web Shell

The PHP web shell is a lightweight upload shell. It will typically be used as an initial staging shell to upload more files to act upon the malicious user’s objectives. To access the functionality of this shell, a user will include ‘login=canshu’ as the parameter value pairing. This allows access to the simple uploader script that can be accessed via a browser or a command line.

Exploitation

Stages

1. The malicious user uploads/downloads the PHP web shell via a vulnerability or other mechanism.
2. The server responds indicating success.
3. The malicious user accesses the PHP shell. The URI will contain ‘login=canshu’.

Prerequisites

The attacker must be able to inject the malicious code onto the web server through another vulnerability or exploit.

Alert Logic Coverage

Alert Logic® has evaluated its customer base for exposure to the exploit and has developed signatures for mitigating the threat depending on the security service in place.

The Network-Based Intrusion Detection System (IDS) has been updated with the new signatures for this exploit when detected via Alert Logic Threat Manager™. If this signature is detected, an incident is generated in the Alert Logic console.

Recommendations for Mitigation

The attacker must have exploited some other entry vector to allow the malicious files to become resident on the victim machine.