CVE-2021-20837

Exp

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.

Published: 2021-10-26 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-20837 is rated High Exploit Risk (89.3/100): CVSS Critical severity, with high exploitation likelihood (EPSS 94.19%, 100th percentile). 2 public exploit reference(s) are indexed (Exploit-DB). Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2021-20837

EDB-ID Source Kind Published Link
50464 exploit_db edb 2021-10-29 Exploit-DB ↗
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2021-20837

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-03-04 94.09% 94.19% +0.09%
2 2026-03-01 94.19% 94.09% -0.09%
3 2026-02-04 — 94.19% —

Full EPSS history (44 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-20837

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
9.8 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 5.9 [email protected]
7.5 2.0 HIGH
AV:N/AC:L/Au:N/C:P/I:P/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:P)
Partial availability impact.
 10.0 6.4 [email protected]

Weakness enumeration for CVE-2021-20837

Affected software / configurations for CVE-2021-20837

Vendor Product Version Raw CPE
sixapart movable_type <= 1.46 cpe:2.3:a:sixapart:movable_type:*:*:*:*:premium:*:*:*
sixapart movable_type <= 1.46 cpe:2.3:a:sixapart:movable_type:*:*:*:*:premium_advanced:*:*:*
sixapart movable_type >= 4.0, <= 6.3.11 cpe:2.3:a:sixapart:movable_type:*:*:*:*:*:*:*:*
sixapart movable_type >= 6.5.0, <= 6.8.2 cpe:2.3:a:sixapart:movable_type:*:*:*:*:-:*:*:*
sixapart movable_type >= 6.5.0, <= 6.8.2 cpe:2.3:a:sixapart:movable_type:*:*:*:*:advanced:*:*:*
sixapart movable_type >= 7.0, <= 7.8.1 cpe:2.3:a:sixapart:movable_type:*:*:*:*:-:*:*:*
sixapart movable_type >= 7.0, <= 7.8.1 cpe:2.3:a:sixapart:movable_type:*:*:*:*:advanced:*:*:*

References for CVE-2021-20837

cvelogic Threat Intelligence