CVE-2021-21344: 
MySQL vulnerability analysis and mitigation

XStream is a Java library to serialize objects to XML and back again. In XStream before version 1.4.16, there is a vulnerability (CVE-2021-21344) which may allow a remote attacker to load and execute arbitrary code from a remote host only by manipulating the processed input stream. The vulnerability was discovered in March 2021 (MITRE, GitHub Advisory).

The vulnerability exists in the unmarshalling process where XStream creates new instances based on type information contained in the processed stream. An attacker can manipulate the input stream and replace or inject objects that result in execution of arbitrary code loaded from a remote server. The vulnerability can be exploited through both XML and JSON formats (XStream Doc). The vulnerability has been assigned a CVSS v3.1 base score of 9.8 (Critical) (Ubuntu).

A successful exploitation of this vulnerability could allow remote attackers to execute arbitrary code in the context of the application running XStream. No user is affected who followed the recommendation to setup XStream's security framework with a whitelist limited to the minimal required types (GitHub Advisory).

The vulnerability is remotely exploitable without requiring authentication. An attacker only needs the ability to manipulate the processed input stream that is used for unmarshalling objects. The vulnerability has been demonstrated using a simple PriorityQueue object that when marshalled to XML and manipulated with malicious content, can trigger remote code execution (XStream Doc).

The vulnerability is fixed in XStream version 1.4.16. Users should upgrade to this version or later. For those unable to upgrade immediately, XStream provides workarounds through its security framework by implementing a whitelist for allowed types. This can be achieved by using XStream's security framework to explicitly define which types are allowed to be unmarshalled (XStream Doc).

Multiple Linux distributions and software vendors responded to this vulnerability by releasing security updates, including Debian, Fedora, and Oracle. NetApp issued an advisory for their affected products (NetApp Advisory).