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

> Attackers can poison cached redirects via X-Forwarded-Host header in Ratpack, forcing users to malicious sites if custom PublicAddress is not configured.

- **Severity:** High 7.0 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 29 Jun 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-w6rq-6h34-vh7q

## What is CVE-2021-29479?

CVE-2021-29479 is a high-severity vulnerability in ratpack, published on 29 Jun 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-807 (Reliance on Untrusted Inputs in a Security Decision)

## Which versions are affected by CVE-2021-29479?

2 open source packages ship an affected version, including io.ratpack:ratpack-core. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `io.ratpack:ratpack-core` | Maven | All versions | 1.9.0 |
| `io.ratpack:ratpack-core` | Maven | All versions | 1.9.0 |

Products: Ratpack Project Ratpack.

## How do I fix CVE-2021-29479?

Upgrade io.ratpack:ratpack-core to 1.9.0 or later.

## Is CVE-2021-29479 being exploited?

There is no known exploitation of CVE-2021-29479 in the wild and no public exploit code.

## Other vulnerabilities in ratpack

- [CVE-2021-29485](https://insights.sbomify.com/CVE-2021-29485/): Remote Code Execution Vulnerability in Session Storage (critical 9.9)
- [CVE-2019-17513](https://insights.sbomify.com/CVE-2019-17513/): io.ratpack:ratpack-core vulnerable to Improper Neutralization of Special Elements in Output ('Injection') (high 7.5)
- [CVE-2021-29481](https://insights.sbomify.com/CVE-2021-29481/): Client side sessions should not allow unencrypted storage (medium 6.5)
- [CVE-2021-29480](https://insights.sbomify.com/CVE-2021-29480/): Default client side session signing key is highly predictable (medium 4.4)
- [CVE-2019-11808](https://insights.sbomify.com/CVE-2019-11808/): Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG) in Ratpack (low 3.7)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-29479 and fix it if it is affected.

What it is: CVE-2021-29479 is a high-severity vulnerability in ratpack, published on 29 Jun 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-29479 in the wild and no public exploit code.

Affected packages and fixed versions:
- io.ratpack:ratpack-core (Maven): affected all versions; fixed in 1.9.0
- io.ratpack:ratpack-core (Maven): affected all versions; fixed in 1.9.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-29479/ (Markdown: https://insights.sbomify.com/CVE-2021-29479/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-29479
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-29479
- OSV: https://osv.dev/vulnerability/CVE-2021-29479

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-29479/
Summaries are generated and may contain mistakes; the official description above is the record.