Detect SMS Pumping in Microsoft Sentinel
Adversaries may leverage messaging services for SMS pumping, a telecommunications fraud technique where the attacker first obtains a block of phone numbers from a carrier, then abuses a victim's SMS infrastructure to generate large volumes of messages to those numbers. The adversary earns per-message payments from the carrier proportional to traffic volume. Attack vectors typically target public-facing web forms — OTP verification, account confirmation, password reset — backed by services such as Twilio, AWS SNS, or Amazon Cognito. Indicators include a spike in SMS API calls from a small set of source IPs, sequential or numerically adjacent destination phone numbers, destination numbers concentrated in high-fraud carrier prefixes, and a sharp increase in SMS-related cloud spend. Unlike volumetric DoS, SMS pumping is financially motivated: the attacker profits directly from the victim's messaging bill.
MITRE ATT&CK
- Tactic
- Impact
- Technique
- T1496 Resource Hijacking
- Sub-technique
- T1496.003 SMS Pumping
- Canonical reference
- https://attack.mitre.org/techniques/T1496/003/
KQL Detection Query
let SMSFormThreshold = 50;
let OTPPatterns = dynamic(["otp", "verify", "verification", "confirm", "sms", "phone", "mobile", "2fa", "mfa", "passcode", "one-time", "send-code"]);
// Branch 1: Application Insights — spike in requests to OTP/phone-verification endpoints
let Branch1 = AppRequests
| where TimeGenerated > ago(1h)
| where Url has_any (OTPPatterns) or Name has_any (OTPPatterns)
| where ResultCode == "200" or ResultCode == "429"
| summarize
RequestCount = count(),
SuccessCount = countif(ResultCode == "200"),
ThrottledCount = countif(ResultCode == "429"),
UniqueURLs = dcount(Url),
SampleURL = any(Url)
by bin(TimeGenerated, 5m), ClientIP, AppRoleName
| where RequestCount >= SMSFormThreshold
| extend DetectionSource = "AppRequests-OTPSpike"
| project TimeGenerated, SourceIP = ClientIP, Service = AppRoleName, RequestCount, UniqueTargets = UniqueURLs, DetectionSource;
// Branch 2: Azure Communication Services diagnostics — abnormal SMS send volume
let Branch2 = AzureDiagnostics
| where TimeGenerated > ago(1h)
| where ResourceType =~ "MICROSOFT.COMMUNICATION/COMMUNICATIONSERVICES"
| where OperationName =~ "SmsSend" or OperationName =~ "SmsDelivery"
| extend RecipientPhone = tostring(column_ifexists("recipientPhoneNumber_s", ""))
| summarize
RequestCount = count(),
UniqueTargets = dcount(RecipientPhone),
FailedCount = countif(ResultType =~ "Failed")
by bin(TimeGenerated, 5m), SourceIP = tostring(callerIpAddress_s), Service = ResourceGroup
| where RequestCount > 100
| extend DetectionSource = "AzureDiagnostics-SMSSpike";
// Combine detection branches
union Branch1, Branch2
| sort by TimeGenerated descDetects SMS pumping via two complementary branches targeting Azure-hosted services: (1) Application Insights AppRequests — identifies a rate spike to OTP/phone-verification form endpoints from a single IP, aggregated over 5-minute windows with a configurable threshold (default 50 requests/window); (2) Azure Communication Services diagnostic logs — fires when the SMS send operation count from a single caller exceeds 100 per 5-minute window. Both branches project matching schemas for union. Tune SMSFormThreshold against your environment's 99th-percentile OTP request baseline.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate bulk SMS marketing or promotional campaigns sending high volume through the same Communication Services resource
- Load testing or security testing of OTP endpoints by internal teams without prior SOC notification
- A viral product launch or viral marketing event driving a legitimate spike in new-user OTP verification requests
- Misconfigured health-check or synthetic monitoring scripts repeatedly hitting verification form endpoints
Other platforms for T1496.003
Testing Methodology
Validate this detection against 4 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1AWS SNS Publish Burst to Phone Number via CLI
Expected signal: AWS CloudTrail: 15 eventName=Publish events from eventSource=sns.amazonaws.com within ~5 seconds, each with requestParameters containing phoneNumber=+15550001234 and message content. Events appear in CloudTrail within ~15 minutes. SNS CloudWatch metric NumberOfMessagesSentToPhoneNumbers increments by 15. SMSMonthToDateSpentUSD increases.
- Test 2Amazon Cognito ForgotPassword OTP Flood
Expected signal: AWS CloudTrail: up to 20 eventName=ForgotPassword events from eventSource=cognito-idp.amazonaws.com within ~10 seconds, all sharing the same sourceIPAddress. requestParameters.username will be consistent across all events. Cognito may throttle after ~5 rapid requests, generating ThrottlingException errors also visible in CloudTrail.
- Test 3OTP Form Endpoint Burst via curl Parallel Requests
Expected signal: Application Insights AppRequests table: 60 request entries for /api/auth/send-otp with identical ClientIP (local machine), ResultCode 200 or 429 (rate-limited), arriving within a ~15-second window. Telemetry visible in Application Insights within 1-2 minutes. If Application Insights SDK is not instrumented in the local app, substitute with reviewing the application access log.
- Test 4Twilio REST API SMS Burst
Expected signal: Twilio Console: 5 outbound messages visible under Monitor > Logs > Messaging Logs within seconds. Twilio REST API: GET /2010-04-01/Accounts/{AccountSid}/Messages.json returns 5 records with Direction=outbound-api, Status=delivered or sent. Twilio usage record increments SMSSent by 5. NOTE: Direct Twilio API calls do NOT generate AWS CloudTrail or Azure Diagnostic events — detection requires Twilio Event Streams ingested into SIEM or Twilio's native fraud scoring dashboard.
References (10)
- https://attack.mitre.org/techniques/T1496/003/
- https://www.twilio.com/en-us/blog/sms-pumping-fraud-solutions
- https://www.twilio.com/docs/glossary/what-is-sms-pumping-fraud
- https://reinforce.awsevents.com/content/dam/reinforce/2024/slides/TDR432_New-tactics-and-techniques-for-proactive-threat-detection.pdf
- https://docs.aws.amazon.com/sns/latest/dg/sms_stats_cloudwatch.html
- https://docs.aws.amazon.com/cognito/latest/developerguide/user-pool-settings-mfa.html
- https://docs.microsoft.com/en-us/azure/communication-services/concepts/analytics/logs/sms-logs
- https://docs.microsoft.com/en-us/azure/azure-monitor/app/asp-net
- https://owasp.org/www-community/attacks/SMS_OTP_Bypass
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1496/T1496.md
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