Hackers Exploit Windmill Flaw to Read Arbitrary Server Files Without Authentication

A high-severity security flaw impacting open-source developer platform Windmill has come under active exploitation in the wild, per VulnCheck.

The vulnerability in question is CVE-2026-29059 (CVSS score: 7.5), a case of unauthenticated path traversal impacting Windmill's "get_log_file" endpoint ("/api/w/{workspace}/jobs_u/get_log_file/{filename}").

"The filename parameter is concatenated into a file path without sanitization, allowing an attacker to read arbitrary files on the server using ../ sequences," according to an advisory published by Windmill in March 2026.

"The primary sensitive value exposed by this vulnerability is the SUPERADMIN_SECRET environment variable, readable via /proc/1/environ. When set, this secret can be used as a Bearer token to authenticate as a superadmin and execute arbitrary code through the job preview API."

However, it's worth noting that SUPERADMIN_SECRET is not set by default, and for standalone Windmill instances without SUPERADMIN_SECRET configured, the impact of the vulnerability is limited to arbitrary file read. The issue has since been addressed in Windmill 1.603.3, released in January 2026, by adding sanitization checks to the filename parameter to prevent directory traversal.