CVE-2021-29479 — ratpack-core
MEDIUMCVE-2021-29479 is a medium-severity (CVSS 6.1) CWE-807 vulnerability in io.ratpack:ratpack-core. 1 public exploit reference exists, so weaponization risk is real. A fix is available for io.ratpack:ratpack-core — see the affected versions and patch details below.
Cached redirect poisoning via X-Forwarded-Host header
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-29479 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
io.ratpack:ratpack-coreReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
Description
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:
- The default PublicAddress implementation no longer infers the address from the request context, instead relying on the configured bind host/port
- 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
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | io.ratpack:ratpack-core | all versions | 1.9.0io.ratpack:ratpack-core:1.9.0 |
Affected Products
ratpackratpack_projectResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for io.ratpack:ratpack-core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update io.ratpack:ratpack-core to 1.9.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-29479 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Frequently Asked Questions
Is CVE-2021-29479 in your dependencies?
Find it across Maven, including transitive dependencies.