CVE-2026-44936: Rancher Fleet has SSRF in Bundle Reader via Unvalidated Helm Repository URL in fleet.yaml

A vulnerability has been identified in Fleet when the helmRepoURLRegex field isn’t set on a GitRepo resource. Fleet’s bundle reader forwards Helm authentication credentials (BasicAuth) to any URL specified in the helm.repo field of a fleet.yaml file.

An attacker with git push access to a Fleet-monitored repository can exploit this behavior by specifying a malicious URL in helm.repo. This causes the Fleet controller to send the configured Helm repository credentials to the attacker’s server.

As a result, the attacker can capture the username and password that an administrator configured to access a private Helm chart repository. However, the response body from the attacker’s server isn’t included in the error message (this behavior was fixed in Fleet v0.13.3 and later), which prevents additional internal data from leaking through the status condition.

The final severity of this vulnerability depends on the specific permissions of the leaked credentials.

Fleet recommends you to:

1. Review your system for potentially leaked credentials.
2. Replace any credentials that might be compromised.

Please consult the associated MITRE ATT&CK - Technique - Stored Data Manipulation and MITRE ATT&CK - Technique - Steal Application Access Token for further information about this category of attack.