Detect SMS Pumping in Elastic Security
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/
Elastic Detection Query
sequence by source.ip with maxspan=5m
[network where
event.category == "network" and
network.protocol in ("http", "https") and
http.request.method in ("POST", "GET") and
(
url.path : (
"*/otp*", "*/verify*", "*/verification*", "*/confirm*",
"*/sms*", "*/phone*", "*/mobile*", "*/2fa*", "*/mfa*",
"*/passcode*", "*/send-code*", "*/send_code*"
) or
url.query : ("*phone*", "*mobile*", "*otp*", "*verify*") or
url.original : (
"*twilio.com*", "*sns.amazonaws.com*", "*vonage.com*",
"*plivo.com*", "*telnyx.com*", "*messagebird.com*"
)
) and
http.response.status_code in (200, 400, 422, 429)
] with runs=50Detects T1496.003 SMS Pumping by identifying a single source IP issuing 50 or more HTTP requests to OTP/phone-verification endpoint paths or known cloud SMS provider API domains within a 5-minute window. The 'runs=50' modifier on the sequence step counts repeated matching events from the same source.ip within the maxspan window. For production deployment, create an Elastic Security Threshold rule using this query with group-by on source.ip and a count threshold of 50 over a 5-minute window. A companion branch can be added using event.provider in ("aws.cloudtrail") and event.action : ("sns:Publish", "GetUserAttributeVerificationCode") for direct cloud API coverage.
Data Sources
Required Tables
False Positives & Tuning
- Load testing or QA automation suites (e.g., k6, Gatling, JMeter) hammering OTP or phone-verification endpoints from a fixed runner IP — coordinate with engineering to whitelist known test source IPs or suppress during scheduled test windows
- High-traffic consumer applications where a promotional event or product launch causes a genuine burst of OTP requests from many real users sharing a corporate NAT or cloud egress IP, breaching the per-IP threshold even though individual user activity is benign
- Automated uptime monitors or synthetic transaction scripts (e.g., Datadog Synthetics, Checkly) that invoke the full OTP verification flow on a short polling interval to verify end-to-end SMS delivery health
- Enterprise SSO or identity provider migration jobs that batch-re-verify phone numbers for large user populations and route all traffic through a single service account IP
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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