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CVE-2021-20837

89
FAUCET Score

CVE-2021-20837 is a critical OS command injection vulnerability affecting multiple versions of Six Apart Movable Type, including Movable Type 7, 6, Advanced, and Premium series, as well as all unsupported versions 4.0 and later. This flaw allows unauthenticated remote attackers to execute arbitrary operating system commands with high impact on confidentiality, integrity, and availability. With a CVSS score of 9.8 and an EPSS score of 0.94, this vulnerability is highly exploitable. While not currently on CISA's KEV catalog, public exploit code, including a Metasploit module and Nuclei templates, is available, indicating a high potential for active exploitation despite limited community discussion or media coverage.

Impacted Technologies

VendorProductVersion(s)CPE
<= 1.46CPE matchmatch criteria
cpe:2.3:a:sixapart:movable_type:*:*:*:*:premium:*:*:*
<= 1.46CPE matchmatch criteria
cpe:2.3:a:sixapart:movable_type:*:*:*:*:premium_advanced:*:*:*
>= 4.0, <= 6.3.11CPE matchmatch criteria
cpe:2.3:a:sixapart:movable_type:*:*:*:*:*:*:*:*
>= 6.5.0, <= 6.8.2CPE matchmatch criteria
cpe:2.3:a:sixapart:movable_type:*:*:*:*:-:*:*:*
>= 6.5.0, <= 6.8.2CPE matchmatch criteria
cpe:2.3:a:sixapart:movable_type:*:*:*:*:advanced:*:*:*

CVSS Data

CVSS version used by this source: 3.1

9.8CRITICAL

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
3.9
Impact Score
5.9
CvssVersion
3.1

Exploit Intelligence

EPSS Score
88.14%
Probability of exploitation in next 30 days
EPSS Percentile
99.8%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
Nuclei: CVE-2021-20837 · Oct 29, 2021
ExploitDB: EDB-50464 · Oct 29, 2021
This CVE's current EPSS score of 0.8814 is in the 99th percentile among its peer group of 36,897 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.3 Bluesky, 0.3 Mastodon, and 2.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Remediation records are not available for this CVE.

References

packetstormsecurity.com / files/164705/Movable-Type-7-r.5002-XMLRPC-API-Remote-Command-Injection.html
ExploitThird Party AdvisoryVDB Entry
packetstormsecurity.com / files/164818/Movable-Type-7-r.5002-XMLRPC-API-Remote-Command-Injection.html
Third Party AdvisoryVDB Entry
jvn.jp / en/jp/JVN41119755/index.html
Third Party Advisory
movabletype.org / news/2021/10/mt-782-683-released.html
Release NotesVendor Advisory