Detect SMS Pumping in Google Chronicle
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/
YARA-L Detection Query
rule sms_pumping_otp_flood_t1496_003 {
meta:
author = "Argus Detection Engineering"
description = "Detects T1496.003 SMS Pumping via high-volume OTP or phone-verification HTTP requests from a single source IP within a 5-minute window, and abuse of cloud SMS provider API endpoints (Twilio, AWS SNS, Vonage, Plivo)."
mitre_attack_tactic = "Impact"
mitre_attack_technique = "T1496.003"
severity = "HIGH"
confidence = "MEDIUM"
platform = "cloud"
created = "2025-01-01"
events:
$req.metadata.event_type = "NETWORK_HTTP"
$req.principal.ip != ""
(
re.regex($req.target.url, `(?i)/(otp|verify|verification|confirm|sms|phone|mobile|2fa|mfa|passcode|send[-_]code)`) or
re.regex($req.target.url, `(?i)(twilio\.com|sns\.amazonaws\.com|nexmo\.com|vonage\.com|plivo\.com|telnyx\.com|messagebird\.com|infobip\.com)`)
)
$ip = $req.principal.ip
match:
$ip over 5m
outcome:
$request_count = count_distinct($req.metadata.id)
$unique_urls = count_distinct($req.target.url)
$risk_score = if(#req > 500, 95, if(#req > 200, 80, 65))
condition:
#req > 50
}Chronicle YARA-L 2.0 rule detecting T1496.003 SMS Pumping. Groups NETWORK_HTTP UDM events by source IP (principal.ip) over a 5-minute sliding window and fires when more than 50 requests match either OTP/phone-verification URL path patterns (via re.regex with case-insensitive flag) or known SMS provider domain substrings in the target URL. Outcome section computes request count, unique URL count, and a risk score for prioritization. Backtick-delimited raw strings are used for regex patterns to avoid double-escaping. Requires ingestion of HTTP access logs or cloud audit logs normalized to the UDM NETWORK_HTTP event type.
Data Sources
Required Tables
False Positives & Tuning
- Shared corporate or cloud NAT egress IPs through which many legitimate users generate OTP requests concurrently, causing per-IP aggregation to breach the threshold even though no individual user is abusing the service
- Continuous integration runners executing automated end-to-end phone verification tests against production infrastructure from a fixed, known CI IP address — suppress via a reference list exclusion on principal.ip
- Mobile backend servers issuing batch OTP verifications during a scheduled user re-enrollment or device migration campaign that processes many accounts within a short window
- Authorized red team or penetration testing exercises targeting OTP and MFA endpoints — coordinate exercise windows and suppress via principal.ip reference list exclusion
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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