CVE-2021-29485: Remote Code Execution Vulnerability in Session Storage

Severity: high (CVSS 8.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 2.0% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-06-29 · updated 2026-06-17
Weakness: CWE-502

Description

Ratpack is a toolkit for creating web applications. In versions prior to 1.9.0, a malicious attacker can achieve Remote Code Execution (RCE) via a maliciously crafted Java deserialization gadget chain leveraged against the Ratpack session store. If one's application does not use Ratpack's session mechanism, it is not vulnerable. Ratpack 1.9.0 introduces a strict allow-list mechanism that mitigates this vulnerability when used. Two possible workarounds exist. The simplest mitigation for users of earlier versions is to reduce the likelihood of attackers being able to write to the session data store. Alternatively or additionally, the allow-list mechanism could be manually back ported by providing an alternative implementation of `SessionSerializer` that uses an allow-list.

Affected products

ratpack: before 1.9.0 — fixed in 1.9.0

How to fix

Upgrade to a fixed version: ratpack 1.9.0. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2021-29485 or the next vulnerability affects your stack