attack-surface.md

Attack Surface Analysis for nikic/php-parser

Attack Surface: Unsanitized Input Leading to PHP Code Injection

• Description: The application parses user-provided input as PHP code without proper sanitization or validation, allowing attackers to inject malicious PHP code that is then processed by the parser.
• How php-parser contributes: php-parser is designed to parse PHP code. When fed unsanitized user input, it will faithfully parse any valid PHP syntax, including malicious code, into an Abstract Syntax Tree (AST). This AST then becomes available for the application to process, potentially leading to code injection vulnerabilities if the application logic is not prepared for malicious AST structures.
• Example: An application allows users to submit PHP code snippets for analysis. If the application directly passes this user input to php-parser without sanitization, an attacker can inject malicious PHP code within the snippet. When parsed, this malicious code is represented in the AST. If the application then uses this AST in a way that leads to code execution or other security-sensitive operations, a PHP code injection vulnerability is created.
• Impact: Full application compromise, remote code execution, data breaches, unauthorized access, denial of service. The impact is severe as attackers can control the application's behavior through injected code.
• Risk Severity: Critical
• Mitigation Strategies:
  • Strict Input Sanitization and Validation: Never directly parse user-provided input without rigorous sanitization and validation. Define a strict whitelist of allowed PHP syntax constructs if possible. Reject any input that deviates from the expected and safe format.
  • Parameterization/Escaping: If the application needs to generate PHP code based on user input, use parameterization or escaping techniques to prevent injection. Treat user input as data, not code.
  • Principle of Least Privilege: Run the parser and application with the minimum necessary privileges to limit the damage if code injection occurs.
  • Sandboxing: Consider executing the parsing process and any subsequent AST-based operations in a sandboxed environment to isolate potential damage from the main application.

Attack Surface: Parser Bugs Leading to Denial of Service (DoS)

• Description: Maliciously crafted PHP code input exploits vulnerabilities or inefficiencies within php-parser's parsing logic, causing excessive resource consumption (CPU, memory) and leading to application slowdown, unresponsiveness, or crashes.
• How php-parser contributes: As a complex software library, php-parser may contain bugs or algorithmic inefficiencies in its parsing engine. Attackers can craft specific PHP code inputs that trigger these vulnerabilities, forcing the parser into computationally expensive operations.
• Example: An attacker crafts a PHP code snippet with deeply nested language constructs, extremely long lines, or complex combinations of language features that expose exponential time complexity or memory leaks in php-parser. When the application attempts to parse this malicious input, php-parser consumes excessive resources, leading to a denial of service for legitimate users.
• Impact: Denial of service, application downtime, resource exhaustion, impacting availability and potentially leading to financial losses or reputational damage.
• Risk Severity: High
• Mitigation Strategies:
  • Resource Limits: Implement strict resource limits (CPU time, memory limits, execution time limits) for the parsing process to prevent runaway resource consumption. Configure these limits based on expected input size and complexity.
  • Input Complexity Limits: If feasible, impose limits on the complexity of the input PHP code, such as maximum nesting depth, maximum line length, or restrictions on certain language features known to be computationally expensive to parse.
  • Regular Updates: Keep php-parser updated to the latest version. Updates often include bug fixes and performance improvements that can address DoS vulnerabilities.
  • Fuzzing and Security Testing: Conduct regular fuzzing and security testing of the application's parser integration with a wide range of PHP code inputs, including intentionally malformed, complex, and edge-case inputs, to proactively identify potential DoS vulnerabilities in php-parser.

Attack Surface: Parser Bugs Leading to Unexpected Parser Behavior and Incorrect AST

• Description: Malicious or unexpected PHP code input triggers bugs within php-parser that result in the generation of an incorrect or incomplete Abstract Syntax Tree (AST). This flawed AST can then lead to security bypasses or incorrect application behavior if the application relies on the AST for security-critical decisions or logic.
• How php-parser contributes: Parser bugs can cause php-parser to misinterpret valid PHP code, leading to an AST that does not accurately represent the intended structure and semantics of the input code. This misrepresentation originates directly from errors within the parser's code.
• Example: A vulnerability in php-parser causes it to incorrectly parse a specific combination of PHP language features related to variable handling or function calls. This results in the AST missing a crucial node representing a security-sensitive operation or misrepresenting the type of a variable. If the application uses this flawed AST for security analysis (e.g., detecting unsafe function calls), the incorrect AST can lead to a security bypass where malicious code is not detected.
• Impact: Security bypasses, incorrect application logic based on flawed AST analysis, potential for further exploitation if the application relies on the AST for security-critical decisions, leading to vulnerabilities like privilege escalation or data manipulation.
• Risk Severity: High
• Mitigation Strategies:
  • Robust AST Processing Logic: Design and implement the application's AST processing logic to be resilient to potential inconsistencies or inaccuracies in the AST. Avoid making assumptions about the AST structure without validation. Implement defensive programming practices when traversing and analyzing the AST.
  • Thorough Testing of AST Handling: Extensively test the application's AST processing code with a wide range of PHP code examples, including complex syntax, edge cases, and potentially problematic language constructs, to identify and address any logic errors arising from incorrect AST interpretation.
  • Regular Updates: Keep php-parser updated to the latest version to benefit from bug fixes that address parser inconsistencies and incorrect AST generation.
  • AST Validation (If Feasible): If possible and practical, implement checks to validate the generated AST against expected structures or known patterns, especially for security-critical code paths. This can help detect potential parser errors leading to flawed ASTs.