NVD / CVE Program· CNA jpcert

CVE-2021-20837: 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

Noroxi assessment

Priority: This week (action score 65/100)

A ready-made attack module is public (Nuclei); exploiting it takes no special expertise.
Public proof-of-concept code exists (Exploit-DB, GitHub); there is no record of exploitation in the wild.
Probability of exploitation in the next 30 days: 88.1% (FIRST EPSS); higher than 99.7% of all records.
Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
According to the record, no fixed version is available yet.

Don’t wait for the next maintenance window. Until a fix is released, restrict access to the affected component and follow the vendor's advisory.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

CriticalCVSS 9.8 · v3.1—Proof of concept No fix recorded

Published: Oct 26, 2021
Updated: Jun 16, 2026
EPSS: 88.1% · 99th percentile
CWE: CWE-78

Report tools

JSON

Action score

This week

Don’t wait for the next maintenance window.

CVSS: 39 / 40 · 9.8 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 26 / 30 · 88.1%

Get told when this record changes

Not in KEV: no record of exploitation in the wild
Proof of concept exists, no weaponized module
No fixed version yet

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
sixapart	movable type	cpe:2.3:a:sixapart:movable_type

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

sixapart movable typeup to 1.46 inclusive
sixapart movable type4.0 and later · up to 6.3.11 inclusive
sixapart movable type6.5.0 and later · up to 6.8.2 inclusive
sixapart movable type7.0 and later · up to 7.8.1 inclusive

Versions reported by the vendor

Affected version ranges reported by the assigning authority (jpcert). Independent of NVD's CPE analysis and usually ahead of it.

Six Apart Ltd. Movable Type
- 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 affected

Same product

sixapart: all records

Other highest-scoring records for the same primary product.

CVE-2013-0209lib/MT/Upgrade.pm in mt-upgrade.cgi in Movable Type 4.2x and 4.3x through 4.38 does not require authentication for requests to database-migr
44Plan
CVE-2022-38078Movable Type XMLRPC API provided by Six Apart Ltd.
40Plan
CVE-2009-0752Unspecified vulnerability in Movable Type Pro and Community Solution 4.x before 4.24 has unknown impact and attack vectors, possibly related
40Plan

Published before and after this one in the same product

← EarlierCVE-2021-20814Aug 25, 2021 · Cross-site scripting vulnerability in Setting screen of ContentType Information Widget Plugin of Movable Type (Movable Type 7 r.4903 and ear
24Monitor
← EarlierCVE-2021-20815Aug 25, 2021 · Cross-site scripting vulnerability in Edit Boilerplate screen of Movable Type (Movable Type 7 r.4903 and earlier (Movable Type 7 Series), Mo
24Monitor
Later →CVE-2020-5669Oct 26, 2021 · Cross-site scripting vulnerability in Movable Type Movable Type Premium 1.37 and earlier and Movable Type Premium Advanced 1.37 and earlier
21Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

No fix version is recorded for this entry. Check the references for vendor advisories.

Exploit status

Proof of concept available

A public proof of concept or detection signature exists. Exploit knowledge is out there; don't delay patching.

Evidence

Exploit-DB entry ×1
Nuclei detection template ×2
Proof-of-concept repository on GitHub ×3

Noroxi does not host or link to exploit code. Metasploit module names and Nuclei template ids are shown (names, not code); Exploit-DB entries and PoC repositories are given as counts only.

Public exploit evidence
Source	Kind	Date
Exploit-DB entry	webapps	2021-10-29
Nuclei detection template	Nuclei template CVE-2021-20837	—
Nuclei detection template	Nuclei template movable-workflow	—
Proof-of-concept repository on GitHub	stars:18	2021-10-25
Proof-of-concept repository on GitHub	stars:21	2021-10-30
Proof-of-concept repository on GitHub	stars:0	2021-11-01

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

First PoCOct 25, 2021-1 d
PublishedOct 26, 2021
TodayOct 30, 2026+1830 d

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
No account or password is required.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality: high · data can be read
Integrity: high · data or configuration can be modified
Availability: high · the service can be disrupted

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality impact: High
Integrity impact: High
Availability impact: High

Weakness class (CWE)

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

CVSS vector

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

nvd-primary

Root cause

User input is inserted as text into a shell command. The shell may interpret special characters in the input as part of the command.

The bug in code

The whole CWE-78 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1const host = req.body.host;
2exec("ping -c 1 " + host, onResult);

Fixed

1const host = req.body.host;
2if (!/^[a-z0-9.-]{1,253}$/i.test(host)) return res.sendStatus(400);
3execFile("ping", ["-c", "1", host], onResult);

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Attack patterns (CAPEC)

ATT&CK techniques

—

Change log

No changes recorded on tracked fields yet. Score, KEV, exploit maturity and fix status changes appear here.

References

packetstormsecurity.com/files/164818/Movable-Type-7-r.5002-XMLRPC-API-Remote-Command-Injection.html

Show all references (2 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records