Bifrost HTTP transport before 2.0.0 accepts an enabled custom plugin whose path is an HTTP URL through unauthenticated POST /api/plugins when management authentication is disabled (the default, governance.auth_config.is_enabled=false). The shared-object loader treats an http-prefixed path as a download URL, writes the body to a temporary .so, and passes it to Go's plugin.Open. After a successful open, optional Init runs immediately with the supplied config as the Bifrost process user. On documented dynamically linked builds (DYNAMIC=1 / no static-link flags), which the vendor requires for custom Go plugins, plugin.Open is expected to succeed and this is unauthenticated remote code execution. On the published statically linked Docker image, plugin.Open fails with Dynamic loading not supported, so that build class is only server-side request forgery. Attack complexity is High because the attacker cannot force RCE on the default static image and a loadable plugin must match the host Go version, OS, architecture, and linkage. The 1.6.x HTTP transport line through 1.6.11 does not contain the fix.
Affects dynamically linked Bifrost binaries that can load Go plugins (DYNAMIC=1), with the management API reachable and governance.auth_config.is_enabled=false (default at disclosure). Linux and macOS only (Go plugin package). The default statically linked Docker image is not RCE-capable; that build class is SSRF only. Confirmed on maximhq/bifrost v1.6.3 for the download-then-plugin.Open path. End-to-end malicious .so load against a DYNAMIC=1 binary was not completed in lab; the RCE score is for the documented custom-plugin build class where plugin.Open is expected to succeed.
A proof of concept issues an unauthenticated POST /api/plugins with enabled=true and path set to an HTTP URL of a Go shared object built for the target Go version and linkage. On a dynamically linked Bifrost binary the loader downloads the body and plugin.Open runs Init in-process (for example writing a marker file as the gateway user). On the official static image the same request downloads the file and then fails with Dynamic loading not supported.
If custom Go plugins are not required, run the statically linked binary or official Docker image so plugin.Open cannot succeed. Otherwise enable dashboard authentication and keep the management listener off untrusted networks.
Upgrade Bifrost HTTP transport to 2.0.0 or later. The fix (PR #5763) refuses create and update of a non-builtin plugin path when the request was let through because dashboard authentication is disabled or unconfigured (403), and replaces the plugin downloader with an SSRF-hardened client. The 1.6.x line through 1.6.11 does not include this change.