threat-modeling.md

Threat Model Analysis for koajs/koa

Threat: Middleware Context Spoofing

• Description: An attacker crafts a malicious request that interacts with a poorly designed custom middleware or misconfigured standard middleware. This middleware, placed before authentication/authorization, incorrectly modifies the ctx.state, ctx.request, or ctx.response object. A subsequent middleware, relying on the modified context, grants unauthorized access. The attacker leverages Koa's middleware chain and context passing mechanism to bypass security.
  • Impact: Unauthorized access to protected resources or functionality. The attacker could gain access to data, perform actions, or escalate privileges they shouldn't have.
  • Affected Component: The interaction between middleware in the Koa application, specifically how ctx is passed and modified. app.use() and the order in which middleware are registered are critical. Vulnerable custom middleware or misconfigured standard middleware (e.g., placing a context-modifying middleware before authentication) are the direct points of failure.
  • Risk Severity: High
  • Mitigation Strategies:
    • Strict middleware ordering: Place authentication/authorization middleware before any middleware that modifies the context in ways that could affect security.
    • Thorough middleware testing: Unit test custom middleware and integration test the middleware chain to ensure correct context handling.
    • Input validation: Validate all data used to modify the ctx object, even within trusted middleware.
    • Use established middleware: Prefer well-vetted authentication/authorization middleware (e.g., koa-passport) and ensure they are configured correctly.
    • Context integrity checks: Validate ctx properties at critical points if upstream modification is a risk, even with seemingly trusted middleware.

Threat: Prototype Pollution via Body Parsing

• Description: An attacker sends a request with a specially crafted JSON payload designed to exploit a vulnerable body-parsing middleware. The payload contains properties like __proto__, constructor, or prototype. If the middleware (e.g., an outdated or misconfigured koa-bodyparser, koa-body, or a custom parser) doesn't properly sanitize these properties, they can be injected into the Object.prototype. This affects all objects in the application, including Koa's ctx object, potentially leading to altered application logic, bypassed security checks, or denial of service. This directly exploits how Koa handles request bodies through middleware.
  • Impact: Wide-ranging, potentially severe. Could lead to arbitrary code execution (in extreme cases), data leakage, denial of service, or bypassing security controls. The impact is amplified because it affects the core ctx object used throughout Koa.
  • Affected Component: Body-parsing middleware that interacts with Koa's request handling. Specifically, middleware like koa-bodyparser, koa-body, or any custom middleware that parses request bodies and merges them into objects without proper sanitization.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Use secure body parsers: Employ only body-parsing middleware that is explicitly known to be secure against prototype pollution. Verify the security advisories and configuration options of the chosen middleware (e.g., ensure a recent, patched version of koa-bodyparser is used with appropriate settings to prevent prototype pollution).
    • Input sanitization: Sanitize and validate all user-supplied data before parsing, even if using a supposedly secure parser. This adds a layer of defense.
    • Object freezing/sealing: Consider freezing or sealing critical objects (like ctx) to prevent prototype modification, although this can be complex to implement correctly.
    • Dependency updates: Regularly update all dependencies, especially body-parsing middleware, to the latest secure versions.
    • Avoid recursive merging: Be extremely cautious with any middleware that recursively merges objects without thorough sanitization.

Threat: Error Handling Information Disclosure

• Description: An unhandled error occurs within a Koa application or its middleware. If the error handling is misconfigured (or absent), Koa's default behavior (or a poorly written custom error handler) might expose sensitive information, such as stack traces, database queries, or internal file paths, to the client. This is a direct consequence of how Koa handles (or doesn't handle) errors and how the developer configures the error response.
  • Impact: Leakage of sensitive information that could aid an attacker in further exploiting the application. The exposed information can reveal details about the application's internal structure, dependencies, and configuration.
  • Affected Component: Koa's error handling mechanism (the app.on('error', ...) event listener) and any custom error handling middleware. The default behavior of Koa if no error handler is provided is a key factor.
  • Risk Severity: High
  • Mitigation Strategies:
    • Custom error handler: Implement a custom error handling middleware that catches all errors and prevents sensitive information from reaching the client.
    • Generic error messages: Return only generic error messages to the client in production. Never expose stack traces, internal paths, or other sensitive details.
    • Secure logging: Log detailed error information (including stack traces) to a secure location only for debugging purposes, and ensure these logs are protected.
    • koa-onerror: Use a dedicated error handling middleware like koa-onerror and configure it correctly for production environments (i.e., to suppress detailed error output).
    • NODE_ENV: Set the NODE_ENV environment variable to production to disable detailed error messages that might be enabled by default in development mode.

Threat: ctx Data Exposure

• Description: A middleware adds sensitive data (e.g., API keys, database credentials) to the Koa ctx object. A subsequent middleware, either intentionally or unintentionally (e.g., through logging or error handling), exposes this data to the client or logs it insecurely. This directly relates to how Koa's ctx object is used as a shared data container across the middleware chain.
  • Impact: Leakage of sensitive credentials, potentially leading to unauthorized access to other systems or data. The severity depends on the nature of the exposed data.
  • Affected Component: Any middleware that adds sensitive data to the ctx object, and any subsequent middleware that logs or otherwise exposes the ctx object (or parts of it). The core issue is the shared nature of the ctx object in Koa.
  • Risk Severity: High
  • Mitigation Strategies:
    • Avoid ctx for secrets: Do not store sensitive data directly in the ctx object. Use environment variables, a secure configuration management system, or a dedicated secrets management solution.
    • Dedicated ctx property: If absolutely necessary to store sensitive data temporarily in ctx, use a dedicated, clearly named property (e.g., ctx.state.secrets) and ensure that this property is never logged or exposed to the client under any circumstances.
    • Redacting logs: Use a logging library with redaction capabilities to prevent sensitive data from being written to logs, even if a middleware attempts to log the entire ctx object.
    • Careful logging: Thoroughly review all logging statements in all middleware to ensure they don't inadvertently include sensitive data from the ctx object.

Threat: Middleware Resource Exhaustion (DoS)

• Description: An attacker sends a large number of requests or specially crafted requests that exploit a vulnerable middleware within Koa's request handling pipeline. This middleware, lacking proper resource limits (e.g., request body size, file upload size, processing time), consumes excessive resources (CPU, memory, disk space), leading to denial of service. This is distinct from general DoS attacks; it targets the specific way Koa processes requests through its middleware chain.
  • Impact: Application unavailability, denial of service to legitimate users.
  • Affected Component: Any middleware within Koa's request handling pipeline that handles resource-intensive operations without proper limits. Examples include body-parsing middleware (koa-bodyparser, koa-body - if misconfigured or outdated), file upload middleware, image processing middleware, or custom middleware performing complex calculations without built-in resource constraints.
  • Risk Severity: High
  • Mitigation Strategies:
    • Request size limits: Use middleware specifically designed to limit the size of request bodies (e.g., koa-bodyparser with explicitly configured size limits). Ensure these limits are enforced.
    • File upload limits: Implement strict limits on file upload sizes and types within the middleware handling uploads.
    • Processing timeouts: Set timeouts for resource-intensive operations within middleware. This prevents a single request from consuming resources indefinitely.
    • Rate limiting: Use rate-limiting middleware (e.g., koa-ratelimit) to prevent attackers from flooding the application with requests, mitigating the impact of resource exhaustion attempts.
    • Resource monitoring: Monitor resource usage (CPU, memory, disk space) and set up alerts for anomalies, allowing for proactive response to potential DoS attacks.