Affected: Homebrew: aider

### Summary A server-side request forgery in LiteLLM Proxy lets an authenticated caller redirect the proxy's outbound request to a host of their choosing by smuggling an `api_base` inside the `user_config` request body, bypassing the existing parameter guard.

### Details LiteLLM Proxy validates request bodies with `is_request_body_safe`, which blocks the `api_base` and `base_url` parameters but does not cover `user_config`. The `user_config` object is used to build the outbound router for a request, so a caller can place an `api_base` inside it and reach an arbitrary host. The guard only inspected the two top-level keys, so the same `api_base` nested inside `user_config` was never checked.

Exploitation requires a valid virtual key.

### Impact An authenticated caller can make the proxy issue server-side requests to internal or external hosts of their choosing, reaching endpoints the caller cannot otherwise access.

### Affected / Patched Affected: `<= 1.83.8` Patched: `1.83.9`

### Remediation Upgrade to 1.83.9 or later (released 2026-04-17).

Affected: BerriAI litellm

LiteLLM is a proxy server (AI Gateway) to call LLM APIs in OpenAI (or native) format. Prior to 1.83.9, an authenticated LiteLLM Proxy caller with a valid virtual key can place api_base inside the user_config request body to bypass is_request_body_safe, which blocks top-level api_base and base_url but previously did not inspect or reject user_config. Because user_config constructs the outbound router, the nested destination redirects a server-side request to an internal or external host selected by the caller and can expose endpoints the caller cannot otherwise access. This issue is fixed in version 1.83.9.