Mitigation Strategy: Lexer Error Handling
Mitigation Strategy: Lexer Error Handling
* **Description:**
1. **Wrap Lexer Calls:** Enclose *all* calls to the Doctrine Lexer's methods (e.g., `setInput()`, `moveNext()`, `lookahead`, `glimpse()`, `tokenize()`) within `try-catch` blocks (or the equivalent error handling mechanism in your programming language). This is crucial because the lexer itself can throw exceptions.
2. **Catch Lexer Exceptions:** Specifically catch exceptions that are thrown by the Doctrine Lexer, most notably `Doctrine\Lexer\LexerException`. Do *not* rely on generic exception handling; be specific.
3. **Fail Fast and Securely:** Inside the `catch` block, *immediately* stop processing the input. Do *not* attempt to "recover" or continue lexing from the point of failure. The lexer's internal state may be compromised.
4. **Log Securely (Avoid Raw Input):** Log the error for debugging purposes, but be *extremely* careful about logging the raw input string that caused the error. It might contain sensitive information or a malicious payload. Log a sanitized version of the input, or just a general error message indicating that a lexing error occurred. Include the lexer's current position *if* it's safe to do so (it might reveal information about the input structure).
5. **Return a Generic Error:** To the user or the calling code, return a *generic* error message that does *not* reveal any internal details about the lexer's state or the specific input that triggered the error. Avoid error messages that could be used for reconnaissance. A simple "Invalid input" or "Parsing error" is usually sufficient.
* **Threats Mitigated:**
* **Information Disclosure (Medium):** Prevents internal details of the lexer's operation, and potentially sensitive parts of the input, from being leaked to an attacker through error messages.
* **Unexpected Application Behavior (Medium):** Ensures that the application handles lexer errors gracefully, preventing it from entering an undefined or inconsistent state. This improves the overall robustness of the application.
* **Denial of Service (DoS) (Low):** While not the primary defense against DoS, proper error handling can prevent *some* DoS attacks that might try to exploit specific error conditions within the lexer.
* **Impact:**
* **Information Disclosure:** Risk is significantly reduced. Proper error handling prevents the leakage of sensitive information.
* **Unexpected Application Behavior:** Risk is significantly reduced. The application becomes more robust and predictable.
* **Denial of Service (DoS):** Risk is slightly reduced. Some DoS vectors might be mitigated.
* **Currently Implemented:**
* Partially implemented in most classes that use the lexer. `try-catch` blocks are present, but the logging is sometimes inconsistent (sometimes logs the raw input, which is a security risk).
* **Missing Implementation:**
* The `ReportGenerator` class completely lacks proper error handling around its lexer calls. Lexer exceptions are not caught, which could lead to uncaught exceptions and application crashes. The logging also needs a thorough review to ensure that no sensitive data is being exposed.
Mitigation Strategy: Regular Expression Timeout (ReDoS Protection) within the Lexer
Mitigation Strategy: Regular Expression Timeout (ReDoS Protection) within the Lexer
* **Description:**
1. **Identify Internal Regexes:** Carefully examine the Doctrine Lexer's source code (or documentation) to identify any regular expressions that are used *internally* by the lexer for token definition. This is crucial because you might not be directly writing these regexes, but the lexer relies on them.
2. **Configuration (If Possible):** If the Doctrine Lexer provides a configuration option to set a timeout for its internal regular expression matching, use it. This is the ideal scenario, as it allows you to control the timeout without modifying the lexer's code.
3. **Custom Lexer (If Necessary):** If the lexer *doesn't* offer a built-in timeout mechanism, you might need to create a custom subclass of the `Doctrine\Lexer\AbstractLexer` (or the specific lexer class you're using). Override the relevant methods (likely those related to token matching) to incorporate a timeout mechanism for regular expression operations. This is a more complex approach, but it might be necessary for robust ReDoS protection. Use a library or your language's built-in features to enforce the timeout.
4. **Handle Timeouts as Errors:** If a regular expression match within the lexer exceeds the timeout, treat this as a lexing error. Throw a `Doctrine\Lexer\LexerException` (or a custom exception that extends it) to signal the failure. This will then be caught by the error handling mechanism described above.
5. **Timeout Value:** A timeout of a few milliseconds (e.g., 10-100ms) is usually sufficient. The exact value should be determined through testing.
* **Threats Mitigated:**
* **Regular Expression Denial of Service (ReDoS) (High):** This directly prevents attackers from crafting input that triggers catastrophic backtracking in the lexer's *internal* regular expressions, leading to a denial-of-service condition.
* **Impact:**
* **Regular Expression Denial of Service (ReDoS):** Risk is significantly reduced (almost eliminated if timeouts are set appropriately and enforced consistently).
* **Currently Implemented:**
* Not implemented anywhere in the project. This is a critical missing security control, as it directly addresses a vulnerability within the lexer itself.
* **Missing Implementation:**
* Missing entirely. The project currently relies on the default behavior of the Doctrine Lexer and the underlying regular expression engine, which may be vulnerable to ReDoS. This needs to be addressed by either configuring a timeout (if supported) or creating a custom lexer subclass.
Mitigation Strategy: Avoid Dynamic Lexer Modification
Mitigation Strategy: Avoid Dynamic Lexer Modification
* **Description:**
1. **Static Lexer Configuration:** Ensure that the Doctrine Lexer's configuration (the set of defined tokens and their corresponding regular expressions or matching rules) is *static* and predetermined. Do *not* allow user input or any external data to modify the lexer's rules at runtime.
2. **Predefined Lexer Instances:** If you need different lexing rules for different contexts, create separate, pre-configured instances of the Doctrine Lexer. Each instance should have a fixed set of rules. Do *not* attempt to dynamically change the rules of a single lexer instance based on user input.
3. **Code Review:** Carefully review the code to ensure that there are no code paths that could allow user input to influence the lexer's configuration, either directly or indirectly.
* **Threats Mitigated:**
* **Code Injection (Critical):** Prevents attackers from injecting malicious code by manipulating the lexer's rules, potentially causing it to recognize arbitrary input as valid tokens.
* **Unexpected Tokenization (High):** Ensures that the lexer's behavior is predictable and consistent, reducing the risk of unexpected tokenization due to dynamically altered rules.
* **Impact:**
* **Code Injection:** Risk significantly reduced (almost eliminated if the lexer configuration is truly static).
* **Unexpected Tokenization:** Risk significantly reduced.
* **Currently Implemented:**
* Mostly implemented. The lexer configurations are generally static, defined in class constants or configuration files.
* **Missing Implementation:**
* Need to audit a newly added feature in `ExperimentalFeatureParser` that uses a slightly different lexer configuration based on a flag loaded from the database. This flag should be strictly controlled and validated to ensure it cannot be manipulated by users. It would be better to have two separate, pre-configured lexer instances.