CVE-2021-20809

Cross-site scripting vulnerability in Create screens of Entry, Page, and Content Type of Movable Type (Movable Type 7 r.4903 and earlier (Movable Type 7 Series), Movable Type 6.8.0 and earlier (Movable Type 6 Series), Movable Type Advanced 7 r.4903 and earlier (Movable Type Advanced 7 Series), Movable Type Premium 1.44 and earlier, and Movable Type Premium Advanced 1.44 and earlier) allows remote attackers to inject arbitrary script or HTML via unspecified vectors.

Published: 2021-08-26 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-20809 is rated Moderate Risk (43.2/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 0.35%). Review affected assets and schedule remediation.

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

Exploit prediction scoring system (EPSS) score for CVE-2021-20809

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 2025-03-30 0.55% 0.35% -0.20%
2 2025-03-29 0.35% 0.55% +0.20%
3 2025-03-17 — 0.35% —

Full EPSS history (10 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-20809

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
6.1 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N 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:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:C)
Breaking this can reach past the original component and bite other resources—bigger blast radius.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 2.8 2.7 [email protected]
4.3 2.0 MEDIUM
AV:N/AC:M/Au:N/C:N/I:P/A:N Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:M)
Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:N)
No availability impact.
 8.6 2.9 [email protected]

Weakness enumeration for CVE-2021-20809

OS Trackers for CVE-2021-20809

vendor priority summary link
ubuntu medium CVE-2021-20809 medium priority: Ubuntu including 1 source packages (movabletype-opensource), 8 status rows across 8 suites (bionic, focal, hirsute, impish, jammy, trusty, upstream, xenial): DNE 6, ignored 1, needs-triage 1. https://ubuntu.com/security/CVE-2021-20809

Affected software / configurations for CVE-2021-20809

Vendor Product Version Raw CPE
sixapart movable_type <= 1.44 cpe:2.3:a:sixapart:movable_type:*:*:*:*:premium:*:*:*
sixapart movable_type <= 1.44 cpe:2.3:a:sixapart:movable_type:*:*:*:*:premium_advanced:*:*:*
sixapart movable_type >= 6.0, <= 6.8.0 cpe:2.3:a:sixapart:movable_type:*:*:*:*:-:*:*:*
sixapart movable_type >= 7.0, < 7.8.0 cpe:2.3:a:sixapart:movable_type:*:*:*:*:-:*:*:*
sixapart movable_type >= 7.0, < 7.8.0 cpe:2.3:a:sixapart:movable_type:*:*:*:*:advanced:*:*:*

References for CVE-2021-20809

cvelogic Threat Intelligence