CVE-2026-59800: 9router: Missing Authorization and OS Command Injection

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 2.0%, percentile 81: FIRST’s model estimates a 2.0% chance of exploitation activity in the next 30 days, higher than 81% of all scored CVEs (elevated). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes 9router (npm) < 0.4.44, fixed in 0.4.44. Check your lockfile, including transitive dependencies.

What it is

9Router before 0.4.44 contains an OS command injection vulnerability in the unauthenticated POST /api/tunnel/tailscale-install endpoint (this route is not covered by the dashboard middleware matcher, so no authorization check is applied). The sudoPassword field from the request body is written to the stdin of a 'sudo -S sh' child process. When sudo does not prompt for a password (the process runs as root, NOPASSWD is configured, or a recent sudo timestamp cache exists), the sudoPassword value is interpreted by sh as a shell command, allowing a remote unauthenticated attacker to execute arbitrary OS commands. Exploitation evidence was first observed by the Shadowserver Foundation on 2026-07-04 (UTC).

From the GitHub advisory

Unauthenticated RCE via /api/tunnel/tailscale-install

Affected: 9router (npm package) — current master (v0.4.39).

Summary

POST /api/tunnel/tailscale-install accepts a JSON body with a sudoPassword field and pipes it, followed by the body of https://tailscale.com/install.sh, into a child process spawned as sudo -S sh. The route is not present in the dashboard middleware matcher in src/proxy.js, so the request reaches the handler without invoking dashboardGuard.proxy(). In deployments where the Node process runs as root (Docker images derived from node: without a USER directive, npm i -g 9router invoked as root, or systemd units without User=), the spawned sh runs as root and executes the attacker-supplied bytes.

Details

Weakness type: CWE-78, CWE-862.

Product: 9router (npm) · Assigned by: VulnCheck · Published: 2026-07-07

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Attack requirements: present (depends on deployment conditions)
• Privileges required: none (no login)
• User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable no, technical impact total.
• FIRST EPSS (model of 2026-10-21): 2.04% probability of exploitation activity in the next 30 days; percentile 81.

Timeline

• 2026-07-02 — GitHub-reviewed advisory GHSA-g6g7-pvmx-m74p published (critical)
• 2026-07-07 — CVE record last updated
• 2026-07-07 — CVE record published by VulnCheck

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vendor and project advisories, patches

1. GitHub Security Advisory (GHSA-g6g7-pvmx-m74p) github.com

Vulnerability records

1. GitHub Advisory GHSA-g6g7-pvmx-m74p github.com
2. CVE.org record CVE-2026-59800 cve.org
3. NVD entry CVE-2026-59800 nvd.nist.gov

Other references from the CVE record and advisory

1. vulncheck.com vulncheck.com
2. github.com github.com

Critical npm advisories · Today’s Security Digest