The REST Plugin in Apache Struts 2.1.x, 2.3.7 through 2.3.33 and 2.5 through 2.5.12 is using an outdated XStream library which is vulnerable and allow perform a DoS attack using malicious request with specially crafted XML payload.
http://www.oracle.com/technetwork/security-advisory/alert-cve-2017-9805-3889403.html
http://www.securityfocus.com/bid/100611
http://www.securitytracker.com/id/1039262
https://security.netapp.com/advisory/ntap-20180629-0001/
https://struts.apache.org/docs/s2-051.html
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170907-struts2
Source: MITRE
Published: 2017-09-20
Updated: 2019-08-12
Type: CWE-20
Base Score: 5
Vector: AV:N/AC:L/Au:N/C:N/I:N/A:P
Impact Score: 2.9
Exploitability Score: 10
Severity: MEDIUM
Base Score: 7.5
Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Impact Score: 3.6
Exploitability Score: 3.9
Severity: HIGH