Code Injection in Stumasy via Mathematical Sentence

Executive Summary

This vulnerability is an unauthenticated PHP code injection in the stumasy project, specifically in the file application/pages/imba_calculator/calculate.php. It occurs because the application directly passes attacker-controlled POST data to the eval() function without any validation or sanitization.

An attacker can send a specially crafted POST request containing malicious PHP code in the value field of a user-supplied JSON array. Since the endpoint does not require authentication, this allows remote attackers to execute arbitrary PHP code on the server.

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Impact Analysis

The impact of this vulnerability can be severe. An attacker can execute arbitrary PHP code on the web server, which may lead to:

• Disclosure of local files
• Writing files into the web root
• Executing operating system commands
• Full compromise of the application and its database, depending on the PHP configuration

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Detection Guidance

This vulnerability can be detected by monitoring for suspicious POST requests sent to the endpoint related to the calculator functionality, specifically targeting the file application/pages/imba_calculator/calculate.php.

Look for POST requests containing JSON data where the 'value' field includes PHP code or suspicious payloads that could be evaluated by the eval() function.

You can use network monitoring tools or web server logs to identify such requests.

• Use curl to test the endpoint with a crafted payload to see if code injection is possible, for example:
• curl -X POST -H "Content-Type: application/json" -d '{"value":"phpinfo();"}' http://yourserver/application/pages/imba_calculator/calculate.php
• Check web server access logs for unusual POST requests to the calculator endpoint.
• Use intrusion detection systems (IDS) or web application firewalls (WAF) to alert on suspicious payloads containing PHP code in POST data.

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Mitigation Strategies

Immediate mitigation steps include preventing unauthenticated access to the vulnerable endpoint and disabling the use of eval() on user-supplied input.

Specifically:

• Restrict access to application/pages/imba_calculator/calculate.php by implementing authentication and authorization controls.
• Sanitize and validate all user inputs before passing them to any code execution functions.
• Remove or replace the use of eval() with safer alternatives that do not execute arbitrary code.
• Monitor logs for exploitation attempts and block suspicious IP addresses.
• If possible, temporarily disable the vulnerable functionality until a patch or fix is available.

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