# Security Audit Report

**Branch**: refactor/decompose-large-handlers
**Base**: main
**Date**: 2025-12-06 22:00 UTC
**Files Analyzed**: 6
**Lines Changed**: ~550 lines added/modified

---

## Executive Summary

This branch performs a refactoring of two handler classes (`DependencyHandler` and `WorkerHandler`) to decompose large methods into smaller, more maintainable functions. Additionally, it introduces a spawn serialization mechanism to fix a TOCTOU (Time-of-Check Time-of-Use) race condition.

**Overall Security Assessment**: **LOW RISK**

The changes are primarily structural refactoring that preserves existing security invariants. No new attack surfaces are introduced. The spawn serialization fix actually **improves** security by preventing a race condition that could lead to resource exhaustion (fork bomb).

---

## BLOCKING Issues in Your Changes

### None Found

After thorough analysis, no blocking security issues were identified in the changed lines.

---

## SHOULD FIX Issues in Code You Touched

### None Found

The refactored code maintains all existing security invariants:

1. **DAG Validation**: Cycle detection and depth limiting remain intact in `DependencyHandler`
2. **Spawn Serialization**: The new mutex pattern correctly prevents TOCTOU races
3. **Resource Monitoring**: Worker spawn limits are preserved
4. **Error Handling**: All error paths properly handle failures without exposing sensitive information

---

## PRE-EXISTING Issues Found (Not Blocking)

These issues existed before this branch and are unrelated to the refactoring changes.

### MEDIUM - Pre-existing Issue #1

**MAX_DEPENDENCY_CHAIN_DEPTH DoS Protection** - `/workspace/delegate/src/services/handlers/dependency-handler.ts:25`

```typescript
const MAX_DEPENDENCY_CHAIN_DEPTH = 100;
```

- **Vulnerability Type**: Denial of Service (DoS) - Limited protection
- **Context**: The depth limit of 100 may be too permissive for some use cases
- **Current State**: Protection exists but may allow excessive memory usage
- **Recommendation**: Consider making this configurable and documenting the memory implications. A chain depth of 100 with complex tasks could consume significant memory in the dependency graph.
- **Reason not blocking**: This is existing behavior, not introduced by this PR. The protection does exist.

### LOW - Pre-existing Issue #2

**Spawn Backoff Fixed Value** - `/workspace/delegate/src/services/handlers/worker-handler.ts:56`

```typescript
private readonly SPAWN_BACKOFF_MS = 1000;
```

- **Vulnerability Type**: Configuration Hardcoding
- **Context**: Backoff value is hardcoded rather than configurable
- **Recommendation**: Consider making this configurable for different deployment environments
- **Reason not blocking**: Does not introduce a security vulnerability, just a configuration limitation

### LOW - Pre-existing Issue #3

**Test Double Security** - `/workspace/delegate/tests/fixtures/test-doubles.ts`

```typescript
// Line 36-37: Map for handlers with 'any' type
private handlers = new Map<string, Set<(event: any) => Promise<void>>>();
private requestHandlers = new Map<string, (event: any) => Promise<Result<any, Error>>>();
```

- **Vulnerability Type**: Type Safety in Tests
- **Context**: Test doubles use `any` types which could hide type errors
- **Recommendation**: Use proper generic types for better type safety
- **Reason not blocking**: Test code only, does not affect production security

---

## Security Analysis by Category

### 1. Input Validation & Injection - PASS

**Analysis of Changed Code:**

The refactored methods in `dependency-handler.ts` do not introduce any new input handling:

- `validateSingleDependency()` - Pure validation, no user input processing
- `handleValidationFailure()` - Logs and emits events, no injection vectors
- `handleDatabaseFailure()` - Logs errors, no injection vectors
- `updateGraphAfterPersistence()` - Internal state update only
- `emitDependencyAddedEvents()` - Event emission with typed parameters

The `worker-handler.ts` changes similarly maintain existing patterns:

- `withSpawnLock()` - Internal concurrency control, no user input
- `getSpawnDelayRequired()` - Pure calculation from internal state
- `handleSpawnDelayRequired()` - Logging and scheduling, no injection vectors
- All extracted methods operate on typed domain objects

**Existing Protection (Not Changed):**
- Branch names sanitized in `worktree-manager.ts:87-89`
- Commit messages sanitized in `worktree-manager.ts:182-188`
- PR titles/bodies sanitized in `worktree-manager.ts:224-229`
- SQL uses prepared statements in database layer

### 2. Authentication & Authorization - N/A

This codebase is an MCP server for task orchestration. It operates locally and does not implement authentication. Tasks are delegated from a trusted main Claude Code instance.

**Note**: This is by design for the MCP architecture where the host application (Claude Code) handles authentication.

### 3. Cryptography & Secrets - PASS

**No secrets found in changed files.**

- No hardcoded API keys, tokens, or passwords
- No cryptographic operations in changed code
- Database path validation exists in `database.ts` (not changed in this PR)

### 4. Race Conditions - IMPROVED

**The key security improvement in this branch:**

The new `withSpawnLock()` mechanism in `worker-handler.ts:225-248` fixes a TOCTOU race condition:

```typescript
/**
 * Execute a function while holding the spawn lock
 * Ensures only one spawn operation runs at a time, eliminating TOCTOU race conditions
 */
private async withSpawnLock<T>(fn: () => Promise<T>): Promise<T> {
  const previousLock = this.spawnLock;
  let releaseLock!: () => void;
  const ourLock = new Promise<void>(resolve => {
    releaseLock = resolve;
  });
  this.spawnLock = ourLock;
  await previousLock;
  try {
    return await fn();
  } finally {
    releaseLock();
  }
}
```

**Before (Vulnerable):**
- Multiple `processNextTask()` calls could check `lastSpawnTime` simultaneously
- All could pass the check before any updated the timestamp
- Result: Burst spawning leading to fork bomb (documented incident 2025-10-04)

**After (Fixed):**
- Promise-chain mutex ensures only one spawn operation runs at a time
- Second caller waits for first to complete
- `try/finally` ensures lock is always released even on errors

**Verdict**: Security improvement, not a vulnerability

### 5. Business Logic - PASS

**Atomicity Invariants Preserved:**

The `handleTaskDelegated()` method maintains all-or-nothing semantics:
1. Validation runs for all dependencies
2. If any validation fails, no database writes occur
3. Graph update only happens after successful database write
4. Events emitted only after graph update

This is verified by characterization tests in:
- `/workspace/delegate/tests/unit/services/handlers/dependency-handler.test.ts:752-778`

### 6. Resource Exhaustion - IMPROVED

**Fork Bomb Prevention:**

The spawn serialization fix directly addresses a resource exhaustion vulnerability:

```typescript
// INCIDENT REFERENCE: 2025-10-04
// Without spawn delay, recovery re-queued 7 tasks → all spawned simultaneously → fork bomb
//
// INCIDENT REFERENCE: 2025-12-06
// Spawn delay alone had TOCTOU race condition - multiple processNextTask() calls
// could pass the delay check before lastSpawnTime was updated. Fixed by adding
// spawn serialization via mutex.
```

**Defense in Depth Layers (All Preserved):**
1. Spawn serialization (NEW) - Only one spawn at a time
2. Spawn delay (`minSpawnDelayMs`) - 10s minimum between spawns
3. Resource monitoring - CPU/memory checks before spawn

### 7. Configuration Security - PASS

**Environment Variable Validation (Pre-existing, Not Changed):**

`/workspace/delegate/src/implementations/database.ts:52-63`:
```typescript
if (!path.isAbsolute(dataDir)) {
  throw new Error('AUTOBEAT_DATA_DIR must be an absolute path');
}
const normalized = path.normalize(dataDir);
if (normalized.includes('..')) {
  throw new Error('AUTOBEAT_DATA_DIR must not contain path traversal sequences (..)');
}
```

Path traversal protection exists for the data directory configuration.

---

## Summary

| Category | Your Changes | Code You Touched | Pre-existing |
|----------|--------------|------------------|--------------|
| CRITICAL | 0 | 0 | 0 |
| HIGH | 0 | 0 | 0 |
| MEDIUM | 0 | 0 | 1 |
| LOW | 0 | 0 | 2 |

**Security Score**: 9/10

**Merge Recommendation**: **APPROVED**

---

## Rationale

1. **No New Vulnerabilities**: The refactoring extracts methods without changing security-relevant behavior
2. **Security Improvement**: The spawn serialization fix addresses a real resource exhaustion vulnerability
3. **Invariants Preserved**: All atomicity, ordering, and validation invariants are maintained
4. **Well Documented**: The `HANDLER-DECOMPOSITION-INVARIANTS.md` document captures critical invariants
5. **Comprehensive Tests**: Characterization tests verify security-relevant behaviors

---

## Verification Checklist

- [x] No hardcoded secrets or credentials
- [x] No SQL injection vectors (uses prepared statements)
- [x] No command injection vectors (uses simple-git library, not shell)
- [x] Input validation maintained
- [x] Race condition fixed (spawn serialization)
- [x] Resource exhaustion protection preserved
- [x] Error handling does not leak sensitive information
- [x] All existing security tests pass

---

## Recommendations for Future Work

1. **Consider configurable depth limit**: `MAX_DEPENDENCY_CHAIN_DEPTH` could be made configurable
2. **Add monitoring**: Consider adding metrics for spawn serialization wait times
3. **Document security model**: Consider adding a `SECURITY.md` documenting the trust model

---

**Report Generated**: 2025-12-06 22:00 UTC
**Auditor**: Claude Code Security Audit Agent
