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ExploitedNot in CISA KEV yet

CVE-2021-20837

Exploitation confirmed. First attested on 2023-10-14 by GCVE · kevintel, GCVE · shadowserver.

  • Published2021-10-26
  • WeaknessCWE-78

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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.

Timeline

dates in UTC
  1. 2021-10-2606:15CVE publishedNVD
  2. 2021-10-29Exploit-DB entryExploit-DB
  3. 2023-10-1414:56Listed as exploited by GCVEGCVE
  4. 2023-10-1414:56Exploitation first reportedGCVE

Observed activity

isMalicious corpus · updated 2026-11-03 21:37 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-20837?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-20837?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD
Sixapart movable type
BranchAffectedFixed in
1.46≤ 1.46no fix published
6.3≥ 4.0, ≤ 6.3.11no fix published
6.x≥ 6.5.0, ≤ 6.8.2no fix published
7.x≥ 7.0, ≤ 7.8.1no fix published

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

Advisories and patches

Detection

read 2026-11-03 22:42 UTC
Nuclei template
available
ProjectDiscovery
Exploit-DB
EDB-50464
Exploit-DB
Proof-of-concept repositories
3 repositories, unverifiedghost-nemesis/cve-2021-20837-pocorangmuda/CVE-2021-20837Cosemz/CVE-2021-20837
PoC-in-GitHub
Metasploit modules
none listed
Metasploit Framework

Sources

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Published
2021-10-26
Last Modified
2026-06-17
NVD status
Modified

Frequently asked questions

What is 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.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.

Is CVE-2021-20837 actively exploited?

Active exploitation of CVE-2021-20837 has not been confirmed. Its EPSS score was 88.1% on 2026-11-03, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-20837?

CVE-2021-20837 has a CVSS v3 base score of 9.8 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

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Sources for this record