CVE-2021-39146: 
Java vulnerability analysis and mitigation

CVE-2021-39146 affects XStream, a simple library used to serialize objects to XML and back again. The vulnerability was discovered in August 2021 and affects all versions up to and including 1.4.17. This vulnerability allows a remote attacker to load and execute arbitrary code from a remote host by manipulating the processed input stream (XStream CVE, GitHub Advisory).

The vulnerability exists in XStream's unmarshalling process where the stream contains type information to recreate previously written objects. During unmarshalling, XStream creates new instances based on this type information. An attacker can manipulate the input stream to replace or inject objects that result in execution of arbitrary code loaded from a remote server. The vulnerability is particularly concerning when using XStream with its default configuration (XStream CVE).

A successful exploitation of this vulnerability could allow remote attackers to execute arbitrary code on the affected system. The vulnerability is rated as HIGH with a CVSS score of 8.5 (CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H) (NetApp Advisory).

The vulnerability was fixed in XStream version 1.4.18, which no longer uses a blacklist by default since it cannot be secured for general purpose. Users are strongly recommended to upgrade to version 1.4.18 or later. Additionally, it is recommended to setup XStream's security framework with a whitelist limited to the minimal required types (GitHub Advisory).

Multiple vendors and organizations responded to this vulnerability by releasing security advisories and patches, including Red Hat, Debian, Oracle, and NetApp. The vulnerability was part of a larger security update that addressed multiple XStream vulnerabilities (Red Hat Advisory, Debian Advisory).