# CVE-2021-29480: Default client side session signing key is highly predictable

> Attackers can tamper with session data if they predict the application startup time, as the default signing key is weak and predictable.

- **Severity:** Medium 4.4 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 29 Jun 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-2cc5-23r7-vc4v

## What is CVE-2021-29480?

CVE-2021-29480 is a medium-severity vulnerability in ratpack, published on 29 Jun 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Ratpack is a toolkit for creating web applications. In versions prior to 1.9.0, the client side session module uses the application startup time as the signing key by default. This means that if an attacker can determine this time, and if encryption is not also used (which is recommended, but is not on by default), the session data could be tampered with by someone with the ability to write cookies. The default configuration is unsuitable for production use as an application restart renders all sessions invalid and is not multi-host compatible, but its use is not actively prevented. As of Ratpack 1.9.0, the default value is a securely randomly generated value, generated at application startup time. As a workaround, supply an alternative signing key, as per the documentation's recommendation.

Weakness: CWE-330 (Use of Insufficiently Random Values), CWE-340 (Generation of Predictable Numbers or Identifiers)

## Which versions are affected by CVE-2021-29480?

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


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

Products: Ratpack Project Ratpack.

## How do I fix CVE-2021-29480?

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

## Is CVE-2021-29480 being exploited?

There is no known exploitation of CVE-2021-29480 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-2021-29479](https://insights.sbomify.com/CVE-2021-29479/): Cached redirect poisoning via X-Forwarded-Host header (high 7.0)
- [CVE-2021-29481](https://insights.sbomify.com/CVE-2021-29481/): Client side sessions should not allow unencrypted storage (medium 6.5)
- [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-2021-29480 and fix it if it is affected.

What it is: CVE-2021-29480 is a medium-severity vulnerability in ratpack, published on 29 Jun 2021. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-29480 in the wild and no public exploit code.

Affected packages and fixed versions:
- io.ratpack:ratpack-session (Maven): affected all versions; fixed in 1.9.0
- io.ratpack:ratpack-session (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-2021-29480/ (Markdown: https://insights.sbomify.com/CVE-2021-29480/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-29480
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-29480
- OSV: https://osv.dev/vulnerability/CVE-2021-29480

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-29480/
Summaries are generated and may contain mistakes; the official description above is the record.