mitigations.md

Mitigation Strategies Analysis for app-vnext/polly

Mitigation Strategy: Bounded Retries with Exponential Backoff and Jitter (using Polly's RetryPolicy)

Description:

1. Identify Retry Points: Locate all instances where Polly's RetryPolicy or WaitAndRetryPolicy is used.
2. Set Maximum Retries: Ensure RetryForever() is never used. Replace with Retry(n) or WaitAndRetryAsync(n, ...) where n is a small, finite number (e.g., 3-5).
3. Implement Exponential Backoff: Use WaitAndRetryAsync with a sleepDurationProvider delegate. Calculate delay: TimeSpan.FromSeconds(Math.Pow(2, attempt)).
4. Add Jitter: Within sleepDurationProvider, add random component: + TimeSpan.FromMilliseconds(_random.Next(0, 100)). Use a thread-safe random number generator.
5. Test: Verify retry logic (number of retries, delays, jitter) with unit/integration tests.

Threats Mitigated:

• DoS Amplification (High Severity): Polly won't flood services with retries.
• Resource Exhaustion (Medium Severity): Limits resources used by retries.
• Covert Channel (Low Severity): Jitter reduces timing predictability.

Impact:

• DoS Amplification: Significantly reduced; retries are strictly bounded.
• Resource Exhaustion: Reduced by limiting retry duration/frequency.
• Covert Channel: Moderate reduction due to randomness.

Currently Implemented:

• OrderService.cs: WaitAndRetryAsync with exponential backoff and jitter for PaymentGateway calls.
• ProductCatalogClient.cs: Retry(3) for fetching product details.

Missing Implementation:

• NotificationService.cs: Uses RetryForever(). Needs bounded retry, backoff, and jitter.
• UserAuthenticationService.cs: Retry(2) without delay/jitter. Needs WaitAndRetryAsync.

Mitigation Strategy: Fallback with Timeouts (using Polly's FallbackPolicy and TimeoutPolicy)

Description:

1. Identify Fallback Policies: Locate FallbackPolicy or FallbackAsync instances.
2. Analyze Fallback Actions: Ensure the fallbackAction delegate is simple and efficient.
3. Minimize Resource Consumption: Avoid complex logic/queries. Prefer cached data (validated) or default values.
4. Implement Timeouts: Wrap fallbackAction with a TimeoutPolicy. Use TimeoutStrategy.Pessimistic (if uninterruptible) or TimeoutStrategy.Optimistic. Example:

   Policy.TimeoutAsync(TimeSpan.FromSeconds(2), TimeoutStrategy.Pessimistic)
         .WrapAsync(Policy.Handle<Exception>().FallbackAsync(...));

5. Test: Verify fallback actions are fast, resource-efficient, and respect timeouts.

Threats Mitigated:

• Resource Exhaustion (Medium Severity): Fallbacks don't consume excessive resources.

Impact:

• Resource Exhaustion: Significantly reduced; fallbacks are lightweight and time-limited.

Currently Implemented:

• ProductService.cs: Fallback returns cached product list (short TTL) with a 2-second timeout.
• RecommendationService.cs: Returns default recommendations with a 1-second timeout.

Missing Implementation:

• OrderProcessingService.cs: Fallback sends email (slow/failable). Needs timeout, simpler fallback.
• AnalyticsService.cs: Fallback performs complex calculation. Simplify or use cached value.

Mitigation Strategy: Policy Ordering (using Polly's PolicyWrap)

Description:

1. Identify Policy Wraps: Locate all PolicyWrap instances.
2. Analyze Policy Order: Security policies (authentication, authorization) must be inside resilience policies (retry, circuit breaker, fallback).
3. Correct Ordering: Refactor if incorrect. Example: authenticationPolicy.Wrap(retryPolicy.Wrap(circuitBreakerPolicy)).
4. Document Rationale: Explain why security policies are inside.
5. Test: Verify security checks happen before resilience logic, even on failures.

Threats Mitigated:

• Bypassing Security Controls (High Severity): Resilience doesn't bypass auth checks.

Impact:

• Bypassing Security Controls: Eliminates this specific bypass risk.

Currently Implemented:

• ApiService.cs: Correctly wraps auth policies inside retry/circuit breaker.
• SecureDataClient.cs: Data access policies applied before retries.

Missing Implementation:

• LegacyIntegrationService.cs: Retry before authentication. Needs correction.
• ExternalServiceClient.cs: Policy order unclear; review and document.

Mitigation Strategy: Circuit Breaker Integration with Retries (using Polly's CircuitBreakerPolicy and RetryPolicy)

Description:

1. Identify Retry Policies: Locate instances where RetryPolicy is used, especially for external dependencies.
2. Combine with Circuit Breaker: Wrap the RetryPolicy with a CircuitBreakerPolicy. This prevents repeated attempts to a failing service after a certain threshold.

   Policy
       .Handle<Exception>()
       .CircuitBreakerAsync(
           exceptionsAllowedBeforeBreaking: 3,
           durationOfBreak: TimeSpan.FromMinutes(1)
       )
       .WrapAsync(retryPolicy); // retryPolicy defined earlier

3. Configure Circuit Breaker:
   • exceptionsAllowedBeforeBreaking: Number of failures before the circuit opens.
   • durationOfBreak: How long the circuit stays open before transitioning to half-open.
4. Test: Simulate sustained failures and verify the circuit breaker opens and closes as expected.

Threats Mitigated:

• DoS Amplification (High Severity): Prevents continued retries to a failing service, reducing load.
• Resource Exhaustion (Medium Severity): Avoids wasting resources on repeated failed attempts.

Impact:

• DoS Amplification: Significantly reduced by stopping requests to a failing service.
• Resource Exhaustion: Reduced by preventing resource consumption on known-to-fail operations.

Currently Implemented:

• ExternalPaymentService.cs: Combines RetryPolicy and CircuitBreakerPolicy for calls to a payment gateway.
• DatabaseClient.cs: Uses a circuit breaker to protect against database connection failures.

Missing Implementation:

• ThirdPartySearchService.cs: Only uses a RetryPolicy. Should be combined with a CircuitBreakerPolicy.
• MessageQueueClient.cs: No circuit breaker; repeated failures could overwhelm the message queue.