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A Denial of Wallet (or cost-amplification attack) is when an attacker calls a function that costs the company money repeatedly, without paying for it—leaving the company to foot the bill. This attack exploits services that are free for users but incur costs for the provider.
Common Attack Vectors
- Cloud Services – Serverless functions (like AWS Lambda) are billed per use. Attackers abuse public-facing APIs to trigger excessive executions.
- Email & SMS – Flooding verification systems with requests drains paid email/SMS credits.
- AI/LLM APIs – Abusing AI chat endpoints (OpenAI, Claude) can rapidly escalate API costs.
You Should Know:
1. Mitigating Cloud Service Abuse (AWS Lambda Example)
AWS Lambda can be abused if not rate-limited. Use AWS WAF and API Gateway throttling:
Set API Gateway rate limiting
aws apigateway create-usage-plan --name "Anti-DoW-Plan" \
--throttle burstLimit=100,rateLimit=50 \
--quota limit=5000,offset=0,period=MONTH
Enable AWS WAF rules to block suspicious IPs
aws wafv2 create-web-acl \
--name "LambdaProtection" \
--scope REGIONAL \
--default-action Allow={} \
--visibility-config SampledRequestsEnabled=true,CloudWatchMetricsEnabled=true,MetricName="LambdaProtection"
2. Preventing Email/SMS Flooding
Implement CAPTCHA and request delays:
Flask example with rate-limiting
from flask_limiter import Limiter
from flask_limiter.util import get_remote_address
app = Flask(<strong>name</strong>)
limiter = Limiter(app, key_func=get_remote_address)
@app.route("/send_verification", methods=["POST"])
@limiter.limit("5 per minute") Max 5 requests/min per IP
def send_verification():
Logic here
3. Securing AI API Endpoints
Restrict OpenAI usage with per-user quotas:
Use API Gateway to meter OpenAI calls aws apigateway create-api-key --name "OpenAI-User-Key" \ --enabled --stage-keys restApiId=API_ID,stageName=prod aws apigateway create-usage-plan-key \ --usage-plan-id PLAN_ID \ --key-id API_KEY_ID \ --key-type API_KEY
What Undercode Say
Denial of Wallet attacks exploit financial dependencies in modern cloud architectures. Key defenses include:
- Rate Limiting (
iptables,fail2ban) - CAPTCHA Enforcement (reCAPTCHA, hCAPTCHA)
- AI Cost Monitoring (AWS Cost Explorer, OpenAI usage alerts)
- Serverless Hardening (AWS Lambda concurrency limits)
Linux Command for IP Blocking:
Block abusive IPs via iptables sudo iptables -A INPUT -p tcp --dport 443 -m recent --name ATTACKER --set sudo iptables -A INPUT -p tcp --dport 443 -m recent --name ATTACKER --update --seconds 60 --hitcount 10 -j DROP
Windows Command for Log Analysis:
Check excessive API calls in Event Logs
Get-WinEvent -LogName "Application" | Where-Object { $_.Message -like "LambdaInvoke" } | Group-Object -Property IP
Expected Output:
A hardened system with:
✅ API rate-limiting
✅ AI/cloud cost alerts
✅ Automated IP blocking
✅ CAPTCHA on free-tier services
References:
Reported By: Aaandrei %F0%9D%90%96%F0%9D%90%A1%F0%9D%90%9A%F0%9D%90%AD%F0%9D%90%AC – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
