Credential Stuffing on Azure

Credential stuffing attacks on Azure APIs exploit the platform's authentication mechanisms by using stolen username-password pairs from data breaches. Attackers leverage automated tools to test these credentials across Azure services, targeting endpoints like Azure Active Directory, Azure Portal, and Azure Resource Manager APIs.

In Azure environments, credential stuffing typically targets authentication endpoints such as:

https://login.microsoftonline.com/common/oauth2/token
https://management.azure.com/providers/Microsoft.Web/sites?api-version=2021-03-01
https://graph.microsoft.com/v1.0/me/messages

Attackers often use compromised credentials from third-party breaches, as users frequently reuse passwords across services. Azure's token-based authentication system becomes vulnerable when attackers successfully authenticate using stolen credentials and then attempt to enumerate resources, modify configurations, or exfiltrate data.

Common Azure-specific attack patterns include:

• Brute-forcing Azure AD credentials to gain organizational access
• Exploiting Azure Resource Manager APIs to enumerate subscriptions and resources
• Targeting Azure Storage accounts using compromised access keys
• Attempting to access Azure Key Vault instances through authenticated API calls

The Azure Security Center and Azure Monitor logs can reveal credential stuffing attempts through patterns of failed authentication from multiple geographic locations, rapid succession of login attempts, or authentication from unusual IP ranges.

Detecting credential stuffing in Azure requires monitoring authentication patterns and API access behaviors. Azure provides several native tools for this purpose:

Azure AD Identity Protection analyzes sign-in patterns and detects anomalies like atypical travel, unfamiliar sign-in properties, or IP address anomalies. It assigns risk levels to users and sign-ins, which can trigger automated responses.

Azure Monitor Logs captures authentication events that can be queried for suspicious patterns:

// Query for suspicious authentication patterns
AzureDiagnostics
| where OperationName == "Sign-in activity"
| where ResultType == "0" // Success
| summarize count() by IPAddress, bin(TimeGenerated, 15m)
| where count_ > 10 // More than 10 successful logins from same IP in 15 minutes

Azure Security Center provides threat detection for identity-related attacks, including credential compromise. It monitors for unusual authentication patterns and can integrate with Azure Sentinel for advanced threat detection.

middleBrick scans Azure API endpoints for credential stuffing vulnerabilities by testing authentication mechanisms without requiring credentials. It evaluates endpoints like Azure Resource Manager APIs for rate limiting weaknesses and authentication bypass opportunities. The scanner identifies endpoints that lack proper authentication controls or have insufficient rate limiting, which are prime targets for credential stuffing attacks.

For Azure Functions and App Services, middleBrick can detect endpoints that expose management APIs or authentication bypass paths that might be exploited during credential stuffing campaigns.

Remediating credential stuffing vulnerabilities in Azure requires a multi-layered approach using native Azure features:

Implement Azure AD Conditional Access to restrict authentication based on risk factors:

// Azure CLI - Create conditional access policy
az conditional-access policy create \
    --display-name "Block credential stuffing" \
    --conditions "{\"applications\":{\"includeApplications\":[\"All\"],\"includeAuthenticationContextClassReferences\":[\"0\"],\"includeUserActions\":[\"SignInRisk\"],\"includeUserActions\":[\"Bypass\"],\"includeUserActions\":[\"mfabypass\"],\"includeUserActions\":[\"compliantDevice\"],\"includeUserActions\":[\"domainJoinedDevice\"]},\"clientApplications\":{\"includeApplications\":[\"All\"],\"includeUserActions\":[\"All\"],\"includeUserActions\":[\"All\"]},\"locations\":{\"includeLocations\":[\"All\"],\"includeUserActions\":[\"All\"]},\"platforms\":{\"includePlatforms\":[\"All\"]},\"signInRiskLevels\":{\"high\":true,\"medium\":true,\"low\":false},\"userRiskLevels\":{\"high\":true,\"medium\":true,\"low\":false},\"users\":{\"includeUsers\":[\"All\"],\"includeGroups\":[\"All\"],\"includeRoles\":[\"All\"]}}" \
    --grant-controls "{\"operator\":\"OR\",\"builtInControls\":[\"block\"],\"customAuthenticationFactors\":[\"\"]}"

Enable Azure AD Smart Lockout to prevent brute-force attacks:

// Azure AD Smart Lockout configuration
az ad umbrella update --smart-lockout-enabled true \
    --smart-lockout-duration 5 \
    --smart-lockout-threshold 10

Implement API Management rate limiting for Azure APIs:

// Azure API Management rate limit policy
<policies>
  <inbound>
    <rate-limit-by-key calls="60" renewal-period="300" 
                     counter-key="@("message.headers["X-Forwarded-For"]")" />
  </inbound>
</policies>

Enable Multi-Factor Authentication (MFA) for all users:

// Enable MFA for all users
az ad user update --user-object-id [USER_ID] --strong-authentication-methods "[
  {
    \"id\": \"https://schemas.microsoft.com/claims/authnmethodsclaims/onpremuserpassword\",
    \"methodType\": \"OneTimePassword\"
  },
  {
    \"id\": \"https://schemas.microsoft.com/claims/authnmethodsclaims/onpremuserpassword\",
    \"methodType\": \"OneTimePassword\"
  }
]"

Monitor and alert on suspicious authentication patterns using Azure Monitor:

// Azure Monitor Alert for credential stuffing
az monitor metrics alert create \
    --name \"CredentialStuffingAlert\" \
    --resource-group \"myResourceGroup\" \
    --scopes \"/subscriptions/[SUBSCRIPTION_ID]\" \
    --condition \"total success count of \"Sign-in activity\" where \"Result Type\" = 0 over the last 5 minutes is greater than 50\" \
    --action email \"[email protected]\"