CVE-2021-20837

CRITICALNVD 9.89.8—
EchelonGraph scoreMEDIUM confidence

This critical-severity CVE scores 9.8 under NVD CVSS v3. EPSS exploit probability: 88.1%, top 0% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, nvd
Weaponized
9.8
EchelonGraph verdictPatch this weekExploitation is likely or a public exploit exists.
  • High exploitation likelihood — EPSS 88%
CISA-KEV: Not listedEPSS: 88%CVSS: 9.8Exploit: NoneExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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.

CVSS v3
9.8
EG Score
9.8(medium)
EG Risk
84(Track*)
EG Risk 84/100SSVC: Track*

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity98% × 45%
Exploitation88% × 40%
Automatability30% × 15%
Action: Watch closely — could escalate to Attend.
EPSS
99.8%
KEV
Not listed

Published

October 26, 2021

Last Modified

November 21, 2024

Advisory Details (4)

Auto-updated Jun 19, 2026
⚠️ Active exploitation confirmed. No patch confirmed yet.
generic

MovableType.org – News:Movable Type 7 r.5003 (v7.8.2), v6.8.3: Security update

https://movabletype.org/news/2021/10/mt-782-683-released.html
generic🔴 Active Exploitation

JVN#41119755: Movable Type XMLRPC API vulnerable to OS command injection

https://jvn.jp/en/jp/JVN41119755/index.html
generic

Temporarily Offline

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

Temporarily Offline

http://packetstormsecurity.com/files/164705/Movable-Type-7-r.5002-XMLRPC-API-Remote-Command-Injection.html

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 5× in last 7d / 13× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-07-24 14:15 UTCEPSS rescore
  2. 2026-07-23 01:56 UTCEG score recompute
  3. 2026-07-22 22:43 UTCEG score recompute
  4. 2026-07-22 14:05 UTCEPSS rescore
  5. 2026-07-19 02:26 UTCEPSS rescore
  6. 2026-07-15 16:55 UTCEPSS rescore
  7. 2026-07-15 16:55 UTCEPSS rescore
  8. 2026-07-07 13:43 UTCEPSS rescore
  9. 2026-07-02 16:57 UTCEPSS rescore
  10. 2026-06-28 04:54 UTCEPSS rescore
  11. 2026-06-28 04:54 UTCEPSS rescore
  12. 2026-06-25 13:48 UTCEPSS rescore
  13. 2026-06-25 13:48 UTCEPSS rescore
  14. 2026-06-23 21:31 UTCEPSS rescore
  15. 2026-06-23 21:31 UTCEPSS rescore
  16. 2026-06-17 17:51 UTCEPSS rescore
  17. 2026-06-15 17:46 UTCEPSS rescore
  18. 2026-06-08 14:15 UTCEPSS rescore
  19. 2026-06-08 14:15 UTCEPSS rescore
  20. 2026-06-07 15:23 UTCEPSS rescore
  21. 2026-06-07 15:23 UTCEPSS rescore
  22. 2026-06-02 20:11 UTCEPSS rescore
  23. 2026-06-02 20:11 UTCEPSS rescore
  24. 2026-05-26 08:28 UTCEG score recompute
  25. 2026-05-26 08:28 UTCGHSA enrichment
Show 3 more
  1. 2026-05-26 07:17 UTCEPSS rescore
  2. 2026-05-26 07:17 UTCEPSS rescore
  3. 2026-05-24 16:49 UTCEPSS rescore

Publicly available exploits

(4 references)

Working exploit code is in the public domain (2 GitHub PoCs) (1 Exploit-DB entry). Defenders should treat patch urgency accordingly — public PoCs typically lead to mass-exploitation within 24-72 hours.

  • GitHub PoCorangmuda/CVE-2021-20837
    First seen Oct 30, 2021

    XMLRPC - RCE in MovableTypePoC

    Open source ↗
  • Exploit-DBEDB-50464✓ verified
    First seen Oct 29, 2021

    Movable Type 7 r.5002 - XMLRPC API OS Command Injection (Metasploit)

    Open source ↗
  • GitHub PoCghost-nemesis/cve-2021-20837-poc
    First seen Oct 25, 2021

    PoC for the CVE-2021-20837 : RCE in MovableType

    Open source ↗
  • Nucleihttp/cves/2021/CVE-2021-20837.yaml
    First seen Jan 1, 2021

    MovableType - Remote Command Injection

    Open source ↗

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2021-20837?
CVE-2021-20837 is a critical vulnerability published on October 26, 2021. 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…
When was CVE-2021-20837 disclosed?
CVE-2021-20837 was first published in the National Vulnerability Database on October 26, 2021, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-20837 actively exploited?
CVE-2021-20837 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 99.8% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-20837?
CVE-2021-20837 has a CVSS v3 base score of 9.8 (NVD).
How do I remediate CVE-2021-20837?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-20837, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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