Auth Bypass in Aws Bedrock

Detecting auth bypass in Aws Bedrock requires examining both infrastructure configurations and runtime behavior. Start with IAM policy analysis to identify overly permissive policies that allow broad model invocation.

middleBrick's Aws Bedrock scanner specifically targets these authentication weaknesses through black-box testing. The scanner attempts unauthenticated API calls to Bedrock endpoints, checking if IAM authentication is properly enforced.

Key detection patterns include:

• Testing InvokeModel endpoints without credentials
• Checking for CORS misconfigurations that expose Bedrock APIs
• Analyzing IAM policies for wildcard permissions
• Detecting exposed model endpoints through API gateway
• Scanning for debug endpoints that bypass auth

middleBrick's LLM security module includes 27 regex patterns specifically designed to detect system prompt leakage in Bedrock responses. These patterns identify ChatML, Llama 2, Mistral, and other format markers that indicate unauthorized access to model internals.

# Using middleBrick CLI to scan Bedrock endpoints
middlebrick scan https://api.example.com/bedrock

# Output includes:
# - Auth bypass risk (A-F score)
# - IAM policy analysis
# - Prompt injection vulnerability detection
# - Model endpoint exposure assessment

The scanner also performs active prompt injection testing with five sequential probes designed for Bedrock's specific response patterns. This includes testing for DAN jailbreak variants that work specifically with Bedrock's model implementations.

CloudTrail log analysis complements black-box scanning by identifying unusual invocation patterns, such as unexpected geographic locations or unusual timing that might indicate unauthorized access.

Remediating auth bypass in Aws Bedrock requires implementing defense-in-depth controls at multiple layers. Start with IAM policy hardening to enforce least privilege access.

// Secure IAM policy for Bedrock access
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {
        "AWS": [
          "arn:aws:iam::123456789012:user/bedrock-user",
          "arn:aws:iam::123456789012:role/bedrock-service"
        ]
      },
      "Action": "bedrock:InvokeModel",
      "Resource": "arn:aws:bedrock:us-east-1:123456789012:model/*",
      "Condition": {
        "Bool": { "aws:MultiFactorAuthPresent": true }
      }
    }
  ]
}

Implement API Gateway with IAM authorization in front of Bedrock endpoints. This adds an additional authentication layer and provides request logging.

// Secure Bedrock wrapper with IAM auth
const { InvokeModel } = require('aws-sdk/clients/bedrock');
const bedrock = new InvokeModel({ region: 'us-east-1' });

app.post('/api/bedrock/secure', async (req, res) => {
  // Verify IAM credentials exist
  if (!req.user || !req.user.sub) {
    return res.status(401).json({ error: 'Authentication required' });
  }
  
  // Check user permissions
  if (!await hasBedrockPermission(req.user.sub)) {
    return res.status(403).json({ error: 'Insufficient permissions' });
  }
  
  try {
    const result = await bedrock.invokeModel({
      modelName: req.body.modelName,
      body: JSON.stringify(req.body)
    }).promise();
    
    res.json(result);
  } catch (error) {
    res.status(500).json({ error: error.message });
  }
});

Implement request validation to prevent prompt injection attacks that could bypass auth through model manipulation.

// Prompt sanitization for Bedrock
function sanitizePrompt(prompt, maxLength = 4000) {
  // Remove suspicious patterns
  const sanitized = prompt
    .replace(/(
|
)/g, ' ') // Remove newlines
    .replace(/(ignore|override|system|instruction)/gi, '') // Remove control words
    .substring(0, maxLength);
  
  return sanitized;
}

Add rate limiting and usage quotas to prevent cost exploitation even if auth bypass occurs.

// Rate limiting for Bedrock usage
const usageTracker = new Map();

async function invokeWithLimits(userId, modelName, prompt) {
  const userUsage = usageTracker.get(userId) || { count: 0, lastReset: Date.now() };
  
  // Daily limit: 100 invocations
  if (Date.now() - userUsage.lastReset > 86400000) {
    userUsage.count = 0;
    userUsage.lastReset = Date.now();
  }
  
  if (userUsage.count >= 100) {
    throw new Error('Daily invocation limit reached');
  }
  
  userUsage.count++;
  usageTracker.set(userId, userUsage);
  
  return await bedrock.invokeModel({ modelName, body: JSON.stringify({ prompt }) }).promise();
}

Enable CloudTrail logging for all Bedrock API calls and set up alerts for unusual patterns. middleBrick's continuous monitoring can automatically scan your Bedrock configurations on a schedule and alert you to auth bypass vulnerabilities.