CVE-2021-29479
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. O3 Security confirms whether CVE-2021-29479 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Cached redirect poisoning via X-Forwarded-Host header
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
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 Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | io.ratpack:ratpack-core | all versions | 1.9.0 |
Research 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. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
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.
How O3 protects you
O3 pinpoints whether CVE-2021-29479 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2021-29479. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2021-29479 in your dependencies?
O3 detects CVE-2021-29479 across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.