OS Command Injection in Six Apart Movable Type

Published: 2021-10-20 | Updated: 2021-10-26
Risk High
Patch available YES
Number of vulnerabilities 1
CVE-ID CVE-2021-20837
Exploitation vector Network
Public exploit Public exploit code for vulnerability #1 is available.
Vulnerable software
Movable Type
Web applications / CMS

Movable Type Advanced
Web applications / CMS

Movable Type Premium
Web applications / CMS

Movable Type Premium Advanced
Web applications / CMS

Vendor Six Apart Ltd

Security Bulletin

This security bulletin contains one high risk vulnerability.

1) OS Command Injection

EUVDB-ID: #VU57555

Risk: High

CVSSv3.1: 8.8 [CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:P/RL:O/RC:C]

CVE-ID: CVE-2021-20837

CWE-ID: CWE-78 - Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')

Exploit availability: Yes


The vulnerability allows a remote attacker to execute arbitrary shell commands on the target system.

The vulnerability exists due to improper input validation in Movable Type XMLRPC API. A remote unauthenticated attacker can send a specially crafted message and execute arbitrary OS commands on the target system.

Successful exploitation of this vulnerability may result in complete compromise of vulnerable system.


Install updates from vendor's website.

Vulnerable software versions

Movable Type: 6.8.2, r.5002

Movable Type Advanced: 6.8.2, r.5002

Movable Type Premium: 1.46

Movable Type Premium Advanced: 1.46

CPE2.3 External links


Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability. However, proof of concept for this vulnerability is available.