SteadyNode Blog
Reduce SSRF risk in URL-based monitoring
A defensive checklist for services that fetch user-supplied URLs: validate destinations, control redirects, and isolate outbound requests.
Treat every submitted URL as untrusted
Accept only the protocols and destination formats your monitoring product needs. Resolve hostnames, reject loopback and private network ranges for both IPv4 and IPv6, and account for cloud metadata addresses.
Revalidate the destination at connection time
DNS answers can change between validation and connection. Resolve and validate the destination close to the request, and repeat checks after every redirect instead of inheriting trust from the original URL.
Enforce outbound limits outside the application
Use an egress policy or isolated worker that can reach only approved public destinations. Add strict time, response-size, and redirect limits, and record blocked requests for operational review without exposing internal network details.
Frequently asked questions
Why are uptime monitors exposed to SSRF?
A monitor that fetches customer-provided URLs can be abused to make requests from its network unless destinations and outbound traffic are restricted.
Is blocking private IP ranges sufficient?
No single check is sufficient. Combine protocol and address validation, redirect revalidation, DNS-aware connection controls, and network-level egress restrictions.
Keep investigating
Related monitoring guides and free tools
- Free toolFree Security Posture Grader PreviewPreview simulated header, TLS, CAA, SPF, and DMARC results. No requests are sent to the entered domain.
- Free toolFree CDN & Gateway Error DecoderTranslate raw Cloudflare 52x, Vercel 504, and CloudFront 502 response headers into actionable fixes.
- Free toolFree JSON Schema ComparatorCompare baseline and new API responses without noisy value diffs.
- Engineering guideSelf-healing browser testsSee how selector changes are suggested, sandbox-verified, and kept under your control.
- Engineering guideDeployment correlationUse timing and changed-file clues to narrow an incident investigation.
Make critical checks part of your routine
Start with the endpoints and customer journeys that matter most, then build coverage as your services grow.
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