Implementation Vulnerabilities - ML-KEM

Overview

Detailed analysis of implementation vulnerabilities, code quality issues, and security weaknesses in the ML-KEM cipher layer implementation.

Current Vulnerabilities: 20 (0 Critical, 8 High, 12 Medium)

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High Severity Vulnerabilities

1. Missing Maximum IV Generation Attempts Validation

Severity: 🟠 HIGH (CVSS 7.0)
Location: MLKEMCipherLayer.ts:467-488
CWE: CWE-754 (Improper Check for Unusual or Exceptional Conditions)

Description: While MAX_IV_GENERATION_ATTEMPTS is set to 100, there's no monitoring or alerting when this limit is approached, which could indicate an attack or implementation issue.

Vulnerable Code:

private async generateUniqueIV(publicKeyBytes: Uint8Array): Promise<Uint8Array> {
  let attempts = 0;
  let iv: Uint8Array;
  
  do {
    iv = crypto.getRandomValues(new Uint8Array(this.IV_LENGTH));
    attempts++;
    if (attempts > this.MAX_IV_GENERATION_ATTEMPTS) {
      throw new CipherLayerError(
        "Failed to generate unique IV after multiple attempts",
        this.name,
        "encrypt"
      );
    }
  } while (this.isIVUsed(ivKey, iv));
  
  return iv;
}

Issues:

• No monitoring when approaching limit
• No alerting for security events
• Could indicate attack or bug
• No logging of security events

Recommendation:

• Add monitoring/alerting when approaching limit
• Log security events
• Consider increasing IV size or using counter-based IVs

---

2. Shared Secret Size Validation Timing

Severity: 🟠 HIGH (CVSS 6.5)
Location: MLKEMCipherLayer.ts:798-804
CWE: CWE-208 (Observable Timing Discrepancy)

Description: Shared secret size validation occurs after decapsulation, potentially leaking timing information about decapsulation success/failure.

Vulnerable Code:

// Perform ML-KEM decapsulation
const sharedSecret = await this.kem.decap({
  recipientKey: privateKey,
  enc: encapsulatedBytes.buffer as ArrayBuffer,
});

// Convert shared secret to Uint8Array
sharedSecretBytes = new Uint8Array(sharedSecret);

// Validate shared secret size immediately after decapsulation
if (sharedSecretBytes.length < this.SHARED_SECRET_MIN_SIZE) {
  throw new CipherLayerError("Decryption failed", ...);
}

Issues:

• Validation occurs after decapsulation
• Timing differs between success/failure
• Could leak information about decapsulation result

Recommendation:

• Validate encapsulated key format before decapsulation
• Use constant-time operations where possible
• Consider validating shared secret size in constant time

---

3. Key Format Validation Complexity

Severity: 🟠 HIGH (CVSS 6.0)
Location: MLKEMCipherLayer.ts:188-269
CWE: CWE-754 (Improper Check for Unusual or Exceptional Conditions)

Description: The getKeyBytes method has complex type checking logic with multiple try-catch blocks that could be exploited for DoS or type confusion attacks.

Vulnerable Code:

private async getKeyBytes(key: Uint8Array | XCryptoKey): Promise<Uint8Array> {
  if (key instanceof Uint8Array) {
    // ... validation
    return key;
  }
  
  if (key && "key" in key && key.key instanceof Uint8Array) {
    // ... validation
    return key.key;
  }
  
  // Try to serialize if it's an XCryptoKey
  if (key && typeof key.type === "string") {
    try {
      const serialized = await this.kem.serializePublicKey(key as XCryptoKey);
      // ... validation
      return bytes;
    } catch (error) {
      try {
        const serialized = await this.kem.serializePrivateKey(key as XCryptoKey);
        // ... validation
        return bytes;
      } catch {
        throw new CipherLayerError("Invalid key format", ...);
      }
    }
  }
  
  throw new CipherLayerError("Invalid key format", ...);
}

Issues:

• Multiple serialization attempts (public then private)
• No early validation of key structure
• Complex type checking logic increases attack surface
• Nested try-catch blocks

Recommendation:

• Simplify key format validation
• Validate key type early (before serialization attempts)
• Add explicit type guards
• Reduce try-catch nesting

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4. Missing Rate Limiting

Severity: 🟠 HIGH (CVSS 6.0)
Location: MLKEMCipherLayer.ts:542-660
CWE: CWE-400 (Uncontrolled Resource Consumption)

Description: No rate limiting on encryption/decryption operations, allowing attackers to exhaust CPU/memory resources.

Impact:

• DoS via resource exhaustion
• CPU exhaustion
• Memory exhaustion
• System instability

Recommendation:

• Implement rate limiting per IP/user
• Add operation quotas
• Monitor resource usage
• Implement circuit breakers

---

5. IV Tracking Key Collision Risk

Severity: 🟠 HIGH (CVSS 5.8)
Location: MLKEMCipherLayer.ts:381-388
CWE: CWE-330 (Use of Insufficiently Random Values)

Description: IV tracking uses first 16 bytes of public key as identifier. While unlikely, hash collisions could cause IV reuse across different keys.

Vulnerable Code:

private getIVTrackingKey(publicKeyBytes: Uint8Array): string {
  const keyPrefix = Array.from(publicKeyBytes)
    .slice(0, 16)
    .map((b) => b.toString(16).padStart(2, "0"))
    .join("");
  return keyPrefix;
}

Issues:

• Uses only first 16 bytes (128 bits)
• Collision probability: ~2^-64 (very low but non-zero)
• Could cause IV reuse across different keys

Recommendation:

• Use full public key hash (SHA-256) instead of prefix
• Or use full public key bytes as Map key
• Document collision probability

---

6. Missing AAD in AES-GCM

Severity: 🟠 HIGH (CVSS 5.5)
Location: MLKEMCipherLayer.ts:608-615
CWE: CWE-345 (Insufficient Verification of Data Authenticity)

Description: AES-GCM encryption does not use Additional Authenticated Data (AAD), which could allow message reordering attacks in certain protocol contexts.

Vulnerable Code:

const ciphertextBuffer = await crypto.subtle.encrypt(
  {
    name: "AES-GCM",
    iv: iv.buffer as ArrayBuffer,
    // Missing: additionalData (AAD)
  },
  aesKey,
  data.buffer as ArrayBuffer,
);

Impact:

• Potential message reordering attacks
• Missing context binding
• Reduced security guarantees

Recommendation:

• Add AAD containing algorithm identifier, version, and public key fingerprint
• Document AAD format
• Ensure AAD is included in protocol specification

---

7. Error Message Information Leakage

Severity: 🟠 HIGH (CVSS 5.3)
Location: MLKEMCipherLayer.ts:648-654, 824-830
CWE: CWE-209 (Information Exposure Through an Error Message)

Description: While error messages are generic, the underlying error object may contain sensitive information that could leak through error chaining or logging.

Recommendation:

• Ensure all error messages are truly generic
• Never include key material, IVs, or ciphertext in errors
• Sanitize error objects before throwing
• Use error codes instead of messages where possible

---

8. Performance Timing Information Exposure

Severity: 🟠 HIGH (CVSS 5.0)
Location: MLKEMCipherLayer.ts:634
CWE: CWE-208 (Observable Timing Discrepancy)

Description: Performance timing is included in metadata, which could leak information about system load, key sizes, or implementation details.

Vulnerable Code:

layerMetadata: {
  algorithm: this.name,
  version: this.version,
  timestamp: Date.now(),
  inputSize: data.length,
  outputSize: ciphertext.length,
  processingTime: endTime - startTime,
  metadata: {
    keyEncapsulation: "ML-KEM-768",
    keyDerivation: "HKDF-SHA256",
    encryption: "AES-GCM-256",
  },
}

Impact:

• Timing side-channel information
• System load information
• Implementation details

Recommendation:

• Remove timing information from production metadata
• Or add jitter to timing measurements
• Document timing exposure risks
• Consider removing metadata entirely in production

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Medium Severity Vulnerabilities

1. Missing Key Rotation Support - No mechanism for key rotation
2. No Key Escrow Protection - Keys could be escrowed by third parties
3. Missing Key Validation - No validation of key material quality
4. No Replay Protection - Missing message replay detection
5. Missing Forward Secrecy - Each encryption uses same public key
6. No Key Compromise Detection - Cannot detect compromised keys
7. Missing Audit Logging - No security event logging
8. No Key Derivation Validation - HKDF parameters not validated
9. Missing Constant-Time Operations - Some operations not constant-time
10. No Memory Protection - Sensitive data not protected from memory dumps
11. Missing FIPS 140-2 Compliance - Not validated for FIPS compliance
12. No Post-Quantum Hybrid Mode - Pure ML-KEM, no hybrid with classical crypto

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Code Quality Issues

Type Safety

Issues:

• Complex type checking in getKeyBytes() method
• Multiple type assertions (as XCryptoKey)
• Type confusion potential

Recommendation:

• Simplify type checking
• Use explicit type guards
• Reduce type assertions

Error Handling

Issues:

• Generic error messages (good)
• But error objects may contain sensitive information
• No error sanitization

Recommendation:

• Sanitize all error objects
• Never include sensitive data in errors
• Use error codes instead of messages

Memory Management

Issues:

• IV tracking memory growth
• No memory limits
• Cleanup may be insufficient

Recommendation:

• Implement memory limits
• More aggressive cleanup
• Monitor memory usage

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Recommendations Summary

Immediate (High Priority)

1. Add rate limiting
2. Enhance IV generation monitoring
3. Simplify key format validation
4. Add AAD to AES-GCM
5. Enhance error handling

Medium-Term (Recommended)

1. Add security test enhancements
2. Implement key rotation support
3. Add replay protection
4. Enhance constant-time operations

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Document Version: 1.0
Last Updated: January 2025