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

Severity: medium (CVSS 6.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.9% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2021-06-29 · updated 2026-06-17
Weakness: CWE-807

Description

Ratpack is a toolkit for creating web applications. In versions prior to 1.9.0, 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. For versions prior to 1.9.0, by default, Ratpack utilizes an inferring version of `PublicAddress` which is vulnerable. 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. The vulnerability was patched in Ratpack 1.9.0. As a workaround, ensure that `ServerConfigBuilder::publicAddress` correctly configures the server in production.

Affected products

ratpack: before 1.9.0 — fixed in 1.9.0

How to fix

Upgrade to a fixed version: ratpack 1.9.0. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2021-29479 or the next vulnerability affects your stack