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

Status: published. Published: 2026-08-20. Updated: 2026-11-08.

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.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: VulnCheck) — https://github.com/decolua/9router/pull/3370

## Affected products and versions

- decolua / 9router (9router): ≥ 0; ≤ 0.5.55 (affected, custom). Source: CNA: VulnCheck

## Severity and prioritization

- CVSS 3.1: 8.5 (high); CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:N; source: CNA: VulnCheck

- CVSS 4.0: 6.3 (medium); CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:H/SI:L/SA:N; source: CNA: VulnCheck

- CISA KEV: No listing in collected sources

- EPSS: 0.38% as of 2026-11-08; percentile 32.71%

- SSVC: exploitation poc; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-918, CWE-184

## Exploit evidence

- exploit: https://github.com/decolua/9router/issues/3293 (ADP: CISA-ADP)

## References

- https://github.com/decolua/9router/issues/3293 (CNA: VulnCheck; issue-tracking)

- https://github.com/decolua/9router/blob/master/src/shared/utils/ssrfGuard.js (CNA: VulnCheck; technical-description)

- https://github.com/decolua/9router/blob/master/src/app/api/provider-nodes/validate/route.js (CNA: VulnCheck; technical-description)

- https://github.com/decolua/9router/pull/3370 (CNA: VulnCheck; issue-tracking, patch)

- https://github.com/decolua/9router (CNA: VulnCheck; product)

- https://www.vulncheck.com/advisories/9router-server-side-request-forgery-via-api-provider-nodes-validate-because-the-ipv4-mapped-ipv6-denylist-check-is-unreachable (CNA: VulnCheck; third-party-advisory)

- https://github.com/decolua/9router/issues/3293 (ADP: CISA-ADP; exploit)

## Provenance

- CNA: VulnCheck: https://www.cve.org/CVERecord?id=CVE-2026-72860; retrieved 2026-11-08; source updated 2026-11-08

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-72860; retrieved 2026-11-08; source updated Not reported

Revision: 3c408d22de2f9a207b6dabf39c032cc73d906139b6d49ae1f1f5d5798d01cf8e

Canonical: https://y2.dev/cve/CVE-2026-72860

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