CVE-2021-29479: Cached redirect poisoning via X-Forwarded-Host header

A user supplied X-Forwarded-Host header can be used to perform cache poisoning of a cache fronting a Ratpack server if the cache key does not include the X-Forwarded-Host header as a cache key.

Users are only vulnerable if they do not configure a custom PublicAddress instance. A custom PublicAddress can be specified by using ServerConfigBuilder::publicAddress. For versions prior to 1.9.0, by default, Ratpack utilizes an inferring version of PublicAddress which is vulnerable.

Impact

This can be used to perform redirect cache poisoning where an attacker can force a cached redirect to redirect to their site instead of the intended redirect location.

Patches

As of Ratpack 1.9.0, two changes have been made that mitigate this vulnerability:

1. The default PublicAddress implementation no longer infers the address from the request context, instead relying on the configured bind host/port
2. Relative redirects issued by the application are no longer absolutized; they are passed through as-is

Workarounds

In production, ensure that ServerConfigBuilder::publicAddress correctly configures the server.

References

• https://portswigger.net/web-security/web-cache-poisoning