Vulnerability record · CVE-2021-20809 · published 26 August 2021

CVE-2021-20809: Sixapart movable type cross-site scripting vulnerability

SSixapart · Movable Type

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.

6.1 CVSS 3.1 Medium EPSS 0.90% · top 41.9% CWE-79 · Cross-site scripting

6.1CVSS 3.1 base score, v2 4.3

0.90%EPSS exploitation probability, 30 days

NoNot in CISA KEV

1Affected product versions listed by NVD

4References

17 Jun 2026Last modified by NVD

Description

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

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

SMovable Type Sixapart

References

Link	Tags
https://jvn.jp/en/jp/JVN97545738/index.html	Third Party Advisory
https://movabletype.org/news/2021/08/mt-780-681-released.html	Release NotesVendor Advisory
https://jvn.jp/en/jp/JVN97545738/index.html	Third Party Advisory
https://movabletype.org/news/2021/08/mt-780-681-released.html	Release NotesVendor Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

10.0CVE-2009-0752Sixapart movable type vulnerabilityUnspecified vulnerability in Movable Type Pro and Community Solution 4.x before 4.24 has unknown impact and attack vectors, possibly related to the p…EPSS 1.4%3 Mar 2009 9.8CVE-2022-38078Sixapart movable type code injection vulnerabilityMovable Type XMLRPC API provided by Six Apart Ltd. contains a command injection vulnerability. Sending a specially crafted message by POST method to …EPSS 2.1%24 Aug 2022 9.8CVE-2021-20837Movable Type XMLRPC API OS command injectionMovable Type 7, 6, Advanced and Premium editions (and all versions 4.0 or later, including EOL releases) contain an OS command injection flaw reachab…EPSS 88%analysed26 Oct 2021 9.8CVE-2016-5742Sixapart movable type sql injection vulnerabilitySQL injection vulnerability in the XML-RPC interface in Movable Type Pro and Advanced 6.x before 6.1.3 and 6.2.x before 6.2.6 and Movable Type Open S…EPSS 1.6%23 Jan 2017 9.3CVE-2026-25776Sixapart movable type code injection vulnerabilityMovable Type provided by Six Apart Ltd. contains a code injection vulnerability which may allow an attacker to execute arbitrary Perl script.EPSS 0.73%8 Apr 2026 8.8CVE-2020-5576Sixapart movable type cross-site request forgery vulnerabilityCross-site request forgery (CSRF) vulnerability in Movable Type series (Movable Type 7 r.4606 (7.2.1) and earlier (Movable Type 7), Movable Type Adva…EPSS 0.84%14 May 2020 8.8CVE-2020-5577Sixapart movable type unrestricted file upload vulnerabilityMovable Type series (Movable Type 7 r.4606 (7.2.1) and earlier (Movable Type 7), Movable Type Advanced 7 r.4606 (7.2.1) and earlier (Movable Type Adv…EPSS 1.7%14 May 2020 7.5CVE-2013-2184Sixapart movable type vulnerabilityMovable Type before 5.2.6 does not properly use the Storable::thaw function, which allows remote attackers to execute arbitrary code via the comment_…EPSS 3.6%27 Mar 2015

Source: NIST National Vulnerability Database (record CVE-2021-20809), CISA KEV, FIRST EPSS (scores of 2026-09-28). This page is refreshed as NVD updates the record.