Windmill flaw exploited: your automation server is exposed

The tools you self-host to automate your business are servers. They have endpoints, they hold secrets, and if you put one on the internet without thinking about it, somebody will find it. Windmill — the open source platform teams use to build internal apps, APIs, workflows, and cron jobs — is the current example. A path traversal bug patched in January is being actively exploited in July, and the reason is the oldest one there is: nobody updated.

What actually happened

The Hacker News reported active in-the-wild exploitation of CVE-2026-29059, an unauthenticated path traversal rated CVSS 7.5. The flaw lives in Windmill's log-fetching endpoint, /api/w/{workspace}/jobs_u/get_log_file/{filename}. Per Windmill's advisory, the filename parameter was concatenated into a file path without sanitization — so ../ sequences walk out of the log directory and read anything the Windmill process can read. No credentials required.

VulnCheck researcher Valentin Lobstein, who reported the flaw and published the full chain, flagged the exploitation. VulnCheck counted roughly 170 vulnerable instances across 24 countries, with attackers pulling /etc/passwd to confirm the read primitive works, and probing both direct Windmill instances and Nextcloud proxy paths.

File read is the floor, not the ceiling. If a deployment sets SUPERADMIN_SECRET, that value is readable through the same bug — and it doubles as a Bearer token for superadmin authentication, which is a straight line to arbitrary code execution on a box that already has credentials for your other systems. That variable isn't set by default, which is the only good news in the advisory.

The fix shipped in Windmill 1.603.3 in January 2026. Six months of patched-and-ignored is what turned a disclosed bug into an exploited one.

Why this matters for your business

Self-hosting is the right call more often than the SaaS vendors would like you to believe. You own the data, you own the uptime, you own the cost curve. What you also own is the patch schedule — and that's the part people skip when they spin up an automation server on a Friday and move on.

An automation platform is the highest-value target in your stack by design. It holds API keys for your payment processor, your CRM, your email provider, your database. It runs arbitrary code on purpose. That's what makes it useful and that's what makes an unauthenticated file read on it a much bigger deal than it sounds.

Do three things today. Check your Windmill version and get to 1.603.3+ if you're behind. Get it off the public internet — automation servers belong behind a VPN or an identity-aware proxy, not on a bare port with a hostname. And rotate anything that server can read, because a file-read bug that's been exploitable since January means "assume the secrets walked" is the responsible default.

Sources: The Hacker News, Valentin Lobstein's writeup.