Ratpack's default client side session signing key is highly predictable

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

4.4 · CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N

EPSS

• CVE-2021-29480: 0.26% estimated exploitation activity in the next 30 days; percentile 18.10 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact 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. Vulnerability Location https://github.com/ratpack/ratpack/blob/29434f7ac6fd4b36a4495429b70f4c8163100332/ratpack-session/src/main/java/ratpack/session/clientside/ClientSideSessionConfig.java#L29 Patches As of Ratpack 1.9.0 the default value is a securely randomly generated value, generated at application startup time. Workarounds Supply an alternative signing key, as per the documentation's recommendation.

Published by the source

1 Jul 2021, 17:02 UTC

Last modified by the source

29 Jan 2023, 05:02 UTC

Source last checked

26 Oct 2026, 16:02 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-2cc5-23r7-vc4v

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# Patch Next advisory brief: CVE-2021-29480

Advisory: Ratpack's default client side session signing key is highly predictable
IDs: CVE-2021-29480, GHSA-2cc5-23r7-vc4v
Record: https://patchnext.com/advisories/cve-2021-29480 (revision 1, source checked 26 Oct 2026, 16:02 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: io.ratpack:ratpack-session 1.9.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven io.ratpack:ratpack-session: affected < 1.9.0; fixed in 1.9.0

## Suggested inspection (read-only)
- Maven io.ratpack:ratpack-session: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on io.ratpack:ratpack-session.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-2cc5-23r7-vc4v (GitHub-reviewed advisory GHSA-2cc5-23r7-vc4v lists affected ranges: Maven io.ratpack:ratpack-session >=0 <1.9.0)

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