1. Introduction
Code Injection vulnerabilities, specifically those exploiting the `php://input` wrapper, allow attackers to execute arbitrary code on a server. This happens when untrusted data from a client is processed as PHP code instead of being treated as regular input. A successful attack can lead to complete server compromise, impacting confidentiality, integrity and availability of systems and data. Web applications using PHP are typically affected.
2. Technical Explanation
- Root cause: Lack of input sanitisation when processing data received via the `php://input` stream.
- Exploit mechanism: An attacker sends a crafted HTTP request with malicious PHP code in the body, which is then executed by the server due to improper handling of the `php://input` wrapper. For example, sending
as part of the POST data could allow remote command execution if ‘cmd’ parameter isn’t filtered. - Scope: Web applications using PHP that directly process user-supplied input without proper validation are affected.
3. Detection and Assessment
Confirming vulnerability requires checking how the application handles raw request bodies. A quick check involves examining the application’s configuration for use of `php://input`. Thorough assessment includes attempting to inject code via a POST request.
- Quick checks: Review PHP configurations (
php.ini) and source code for references to `php://input`. - Scanning: Burp Suite or OWASP ZAP can be used with custom payloads designed to exploit the `php://input` wrapper. These are examples only, as scanner accuracy varies.
- Logs and evidence: Check web server logs for error messages related to PHP execution errors when sending malicious input via POST requests. Look for patterns indicating code execution attempts.
# Example command placeholder:
# No specific command available without knowing the target application's configuration.
# Reviewing php.ini is a good starting point.
4. Solution / Remediation Steps
The primary solution is to avoid processing untrusted input as server-side code. Validate all user inputs and ensure they contain only the expected data types and formats.
4.1 Preparation
- Stop the web service to prevent further exploitation during remediation.
- Roll back plan: Restore from backup or revert code changes if issues arise. A change window may be needed for production systems, requiring approval from relevant teams.
4.2 Implementation
- Step 2: Sanitize the input to remove or escape any potentially malicious characters or code.
- Step 3: If possible, avoid using `php://input` altogether and use alternative methods for handling request bodies (e.g., parsing POST parameters).
4.3 Config or Code Example
Before
After
4.4 Security Practices Relevant to This Vulnerability
Several security practices help prevent code injection vulnerabilities. Least privilege limits the damage from successful attacks, while input validation blocks malicious data. Safe defaults reduce the risk of misconfiguration.
- Practice 2: Least Privilege – Run web applications with the minimum necessary privileges to limit potential damage from successful exploitation.
4.5 Automation (Optional)
Automated code scanning tools can help identify instances of `php://input` usage and potentially vulnerable code patterns.
# Example Bash script snippet for finding php://input in files:
# grep -rn "php://input" /path/to/web/application
5. Verification / Validation
Confirm the fix by attempting to inject code again and verifying that it is not executed. Check web server logs for any errors or unexpected behaviour.
- Post-fix check: Send a malicious payload via POST request (e.g.,
) and verify that the server does not execute the code. The response should indicate an error or invalid input, not successful command execution. - Re-test: Re-run the scanning methods used in detection to confirm the vulnerability is no longer present.
- Monitoring: Monitor web server logs for any attempts to exploit the `php://input` wrapper or other code injection vulnerabilities. Look for error messages related to invalid input or PHP execution errors.
# Post-fix command and expected output (example):
# curl -X POST -d "" http://target/endpoint
# Expected Output: 400 Bad Request, or an error message indicating invalid input.
6. Preventive Measures and Monitoring
Regular security baselines and pipeline checks help prevent code injection vulnerabilities. A robust patch process ensures timely updates to address known issues.
- Baselines: Update security baselines or policies to include requirements for input validation and secure coding practices.
- Asset and patch process: Implement a regular patch management cycle to address known vulnerabilities in PHP and related libraries.
7. Risks, Side Effects, and Roll Back
- Risk or side effect 1: Overly strict input validation may prevent valid user data from being submitted. Mitigation: Carefully review and adjust validation rules to allow only necessary characters and formats.
- Roll back: Restore the application’s configuration files and database from backup if issues arise. Revert any code changes made during remediation.
8. References and Resources
Link only to sources that match this exact vulnerability. Use