ZenML 0.57.0 through 0.94.2 relies on the X-Forwarded-For header to determine the client host when Uvicorn is started with the flags --proxy-headers --forwarded-allow-ips *. The rate limiter records requests by this client host; an attacker who can rotate the X-Forwarded-For header can alter the perceived client address and thereby evade the limiter. This flaw allows unthrottled attempts against the POST /api/v1/login and self password‑guessing password endpoints, making credential‑guessing attacks feasible at unlimited speed.

The vulnerability affects the open‑source ZenML platform maintained by zenml-io, specifically release series 0.57.0 up to and including 0.94.2, when deployed with a Uvicorn configuration that accepts forwarded headers from all IP addresses ("--proxy-headers --forwarded-allow-ips *").

With a CVSS score of 6.5 the threat is considered medium severity, while an EPSS of less than 1% indicates a low likelihood of exploitation in the wild. The issue is not listed in the CISA KEV catalog. Attackers can exploit the flaw remotely by sending a large number of POST requests, each rotating the X-Forwarded-For header to bypass the rate limiter and perform rapid credential guessing.