Remote Code Execution Vulnerability in Session Storage

Vulnerability

Ratpack versions prior to 1.9.0 contain an insecure deserialization vulnerability in the session store. An attacker who can write to the session data store (server-side storage) or obtain the secrets used to encrypt/sign client-side session cookies can craft malicious serialized objects. When the application deserializes session data, the attacker's gadget chain can execute arbitrary code. Applications that do not use Ratpack's session mechanism are not affected. [1][2]

Exploitation

An attacker needs either write access to the server-side session data store (e.g., a database) or the ability to decrypt and re-encrypt client-side session cookies. With that access, the attacker can inject a malicious serialized Java object (gadget chain) into session data. Ratpack's default deserialization of the stored object triggers the chain, leading to code execution. The exact payload depends on the serialization mechanism used. [2]

Impact

Successful exploitation yields remote code execution (RCE) with the privileges of the application. The attacker can execute arbitrary commands on the server, compromising confidentiality, integrity, and availability. [1][2]

Mitigation

Ratpack 1.9.0 introduces a strict allow-list mechanism via SessionSerializer and SessionTypeFilter that mitigates the vulnerability. Users of earlier versions should upgrade to 1.9.0 or later. Workarounds include reducing the likelihood of attackers writing to the session data store, or manually backporting the allow-list by providing an alternative SessionSerializer implementation. [1][2]