CVE-2021-20837

Name: CVE-2021-20837
Creator: NVD / NIST
Published: 2021-10-26T06:15:06.987+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9.8/10EPSS 88.14%

Last modified Jun 17, 2026

CVE-2021-20837 is a critical-severity vulnerability rated 9.8/10 on the CVSS scale. Movable Type 7 r.5002 and earlier (Movable Type 7 Series), Movable Type 6.8.2 and earlier (Movable Type 6 Series), Movable Type Advanced 7 r.5002 and earlier (Movable Type Advanced 7 Series), Movable Type Advanced 6.8.2 and earlier (Movable Type Advanced 6 Series), Movable Type Premium 1.46 and earlier, and Movable Type Premium Advanced 1.46 and earlier allow remote attackers to execute arbitrary OS commands via unspecified vectors. Note that all versions of Movable Type 4.0 or later including unsupported (End-of-Life, EOL) versions are also affected by this vulnerability.. EPSS estimates a 88.14% chance of exploitation in the next 30 days.

Description

Movable Type 7 r.5002 and earlier (Movable Type 7 Series), Movable Type 6.8.2 and earlier (Movable Type 6 Series), Movable Type Advanced 7 r.5002 and earlier (Movable Type Advanced 7 Series), Movable Type Advanced 6.8.2 and earlier (Movable Type Advanced 6 Series), Movable Type Premium 1.46 and earlier, and Movable Type Premium Advanced 1.46 and earlier allow remote attackers to execute arbitrary OS commands via unspecified vectors. Note that all versions of Movable Type 4.0 or later including unsupported (End-of-Life, EOL) versions are also affected by this vulnerability.

Metrics

CVSS 3.1

9.8/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Probability

88.14%

99.7th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-78

Affected Software

Vendor	Product	Versions
Sixapart	Movable Type	<= 1.46
Sixapart	Movable Type	>= 4.0, <= 6.3.11
Sixapart	Movable Type	>= 6.5.0, <= 6.8.2
Sixapart	Movable Type	>= 7.0, <= 7.8.1

References

http://packetstormsecurity.com/files/164705/Movable-Type-7-r.5002-XMLRPC-API-Remote-Command-Injection.htmlExploit, Third Party Advisory, VDB Entry
http://packetstormsecurity.com/files/164818/Movable-Type-7-r.5002-XMLRPC-API-Remote-Command-Injection.htmlThird Party Advisory, VDB Entry
https://jvn.jp/en/jp/JVN41119755/index.htmlThird Party Advisory
https://movabletype.org/news/2021/10/mt-782-683-released.htmlRelease Notes, Vendor Advisory
http://packetstormsecurity.com/files/164705/Movable-Type-7-r.5002-XMLRPC-API-Remote-Command-Injection.htmlExploit, Third Party Advisory, VDB Entry
http://packetstormsecurity.com/files/164818/Movable-Type-7-r.5002-XMLRPC-API-Remote-Command-Injection.htmlThird Party Advisory, VDB Entry
https://jvn.jp/en/jp/JVN41119755/index.htmlThird Party Advisory
https://movabletype.org/news/2021/10/mt-782-683-released.htmlRelease Notes, Vendor Advisory

Timeline

Published: Oct 26, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-20837?

How severe is CVE-2021-20837?

CVE-2021-20837 has a CVSS score of 9.8/10 (CRITICAL severity). The EPSS model estimates a 88.14% probability of exploitation in the next 30 days.

How do I fix CVE-2021-20837?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-20837?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST