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CVE-2026-59800 – Unauthenticated OS Command Injection (RCE) – 9Router before v0.4.44

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Summary

CVE-2026-59800 is a critical OS command injection vulnerability in 9Router (decolua/9router), an AI coding proxy designed for internet-facing VPS and cloud deployments, affecting all versions before 0.4.44. The vulnerability exists in the POST /api/tunnel/tailscale-install endpoint, which is absent from the application’s authentication middleware matcher, allowing any unauthenticated remote attacker to reach it and inject arbitrary shell commands. Rated 9.8 Critical (CVSS v3.1) and 9.2 Critical (CVSS v4.0), this vulnerability has been confirmed as actively exploited in the wild since July 4, 2026.

Technical details

  • Root cause (CWE-862 — Missing Authorization): The /api/tunnel/tailscale-install route is not included in the Next.js middleware matcher inside src/proxy.js, meaning dashboardGuard.proxy() is never invoked and no authentication check is applied to requests reaching this endpoint.
  • Root cause (CWE-78 — OS Command Injection): The endpoint reads a sudoPassword field from the JSON request body and writes it directly to the stdin of a sudo -S sh child process, alongside the body of the Tailscale install script. No sanitization or validation is performed on this input.
  • Trigger conditions: Exploitation succeeds when the 9Router Node.js process runs as root (the default in Docker images derived from node:* without a USER directive, or when installed globally via npm i -g as root), when NOPASSWD is configured for sudo, or when a valid sudo timestamp cache exists. All three conditions are common in typical self-hosted deployments.
  • Attack vector: A single unauthenticated HTTP POST request over the network; no credentials, user interaction, or prior access are required.
  • Impact: Full remote OS command execution on the host running 9Router, inheriting root privileges in the most common deployment configurations — enabling complete system takeover, data exfiltration, and lateral movement.
  • Active exploitation: The Shadowserver Foundation first observed exploitation evidence on July 4, 2026 (UTC), three days before CVE publication.

Affected software

  • 9router (npm package, vendor: decolua) — all versions before 0.4.44

Severity

  • CVSS v3.1 base score: 9.8 Critical
  • Vector string: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  • CVSS v4.0 score: 9.2 Critical (CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N)

Mitigation and recommended actions

  • Immediate: Upgrade 9router to version 0.4.44 or later, which moves the Tailscale install route inside the authenticated middleware matcher and removes the unauthenticated code execution path.
  • If immediate patching is not possible: Block external network access to the 9Router dashboard port (default: 20128) via firewall or network-level controls; restrict access to trusted IP ranges only.
  • Hardening: Ensure the 9Router Node.js process does not run as root — use a dedicated non-root user and avoid NOPASSWD sudo configurations.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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