Litestar is an Asynchronous Server Gateway Interface (ASGI) framework. In version 2.17.0, rate limits can be completely bypassed by manipulating the X-Forwarded-For header. This renders IP-based rate limiting ineffective against determined attackers. Litestar's RateLimitMiddleware uses `cache_key_from_request()` to generate cache keys for rate limiting. When an X-Forwarded-For header is present, the middleware trusts it unconditionally and uses its value as part of the client identifier. Since clients can set arbitrary X-Forwarded-For values, each different spoofed IP creates a separate rate limit bucket. An attacker can rotate through different header values to avoid hitting any single bucket's limit. This affects any Litestar application using RateLimitMiddleware with default settings, which likely includes most applications that implement rate limiting. Version 2.18.0 contains a patch for the vulnerability.

Affected: PyPI: litestar

While testing Litestar's RateLimitMiddleware, I discovered that rate limits can be completely bypassed by manipulating the X-Forwarded-For header. This renders IP-based rate limiting ineffective against determined attackers.

## The Problem

Litestar's RateLimitMiddleware uses `cache_key_from_request()` to generate cache keys for rate limiting. When an X-Forwarded-For header is present, the middleware trusts it unconditionally and uses its value as part of the client identifier.

Since clients can set arbitrary X-Forwarded-For values, each different spoofed IP creates a separate rate limit bucket. An attacker can rotate through different header values to avoid hitting any single bucket's limit.

Looking at the relevant code in `litestar/middleware/rate_limit.py` around [line 127](https://github.com/litestar-org/litestar/blob/26f20ac6c52de2b4bf81161f7560c8bb4af6f382/litestar/middleware/rate_limit.py#L127), there's no validation of proxy headers or configuration for trusted proxies.

## Reproduction Steps

Here's a minimal test case

```python from litestar import Litestar, get from litestar.middleware.rate_limit import RateLimitConfig import uvicorn

@get("/api/data") def get_data() -> dict: return {"message": "sensitive data"}

rate_config = RateLimitConfig(rate_limit=("minute", 2))

app = Litestar( route_handlers=[get_data], middleware=[rate_config.middleware] )

if __name__ == "__main__": uvicorn.run(app, host="0.0.0.0", port=8000) ```

Testing the bypass…

Affected: PyPI: litestar

While testing Litestar's RateLimitMiddleware, I discovered that rate limits can be completely bypassed by manipulating the X-Forwarded-For header. This renders IP-based rate limiting ineffective against determined attackers.

## The Problem

Litestar's RateLimitMiddleware uses `cache_key_from_request()` to generate cache keys for rate limiting. When an X-Forwarded-For header is present, the middleware trusts it unconditionally and uses its value as part of the client identifier.

Since clients can set arbitrary X-Forwarded-For values, each different spoofed IP creates a separate rate limit bucket. An attacker can rotate through different header values to avoid hitting any single bucket's limit.

Looking at the relevant code in `litestar/middleware/rate_limit.py` around [line 127](https://github.com/litestar-org/litestar/blob/26f20ac6c52de2b4bf81161f7560c8bb4af6f382/litestar/middleware/rate_limit.py#L127), there's no validation of proxy headers or configuration for trusted proxies.

## Reproduction Steps

Here's a minimal test case

```python from litestar import Litestar, get from litestar.middleware.rate_limit import RateLimitConfig import uvicorn

@get("/api/data") def get_data() -> dict: return {"message": "sensitive data"}

rate_config = RateLimitConfig(rate_limit=("minute", 2))

app = Litestar( route_handlers=[get_data], middleware=[rate_config.middleware] )

if __name__ == "__main__": uvicorn.run(app, host="0.0.0.0", port=8000) ```

Testing the bypass…

Withdrawn by the publisher.

Affected: Ubuntu:25.04: litestar

Litestar is an Asynchronous Server Gateway Interface (ASGI) framework. In version 2.17.0, rate limits can be completely bypassed by manipulating the X-Forwarded-For header. This renders IP-based rate limiting ineffective against determined attackers. Litestar's RateLimitMiddleware uses `cache_key_from_request()` to generate cache keys for rate limiting. When an X-Forwarded-For header is present, the middleware trusts it unconditionally and uses its value as part of the client identifier. Since clients can set arbitrary X-Forwarded-For values, each different spoofed IP creates a separate rate limit bucket. An attacker can rotate through different header values to avoid hitting any single bucket's limit. This affects any Litestar application using RateLimitMiddleware with default settings, which likely includes most applications that implement rate limiting. Version 2.18.0 contains a patch for the vulnerability.