How severe is CVE-2021-20808?

CVE-2021-20808 has a CVSS 3.x base score of 6.1, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2021-20808 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (55th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-20808?

CVE-2021-20808 primarily affects Sixapart Movable Type. In total, 4 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-20808?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-20808 published?

CVE-2021-20808 was published on 2021-08-26 and last updated on 2026-06-17.

CVE-2021-20808

CVE-2021-20808 is a medium-severity vulnerability in Sixapart Movable Type with a CVSS 3.x base score of 6.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-79.

Key facts

Severity: Medium (CVSS 3.x base score 6.1)
CVSS v2: 4.3
EPSS exploit prediction: 1% (55th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-79
Affected product: Sixapart Movable Type
Published: 2021-08-26
Last modified: 2026-06-17

Description

Cross-site scripting vulnerability in Search screen 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.

Frequently asked questions

What is CVE-2021-20808?: Cross-site scripting vulnerability in Search screen 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.
How severe is CVE-2021-20808?: CVE-2021-20808 has a CVSS 3.x base score of 6.1, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2021-20808 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (55th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-20808?: CVE-2021-20808 primarily affects Sixapart Movable Type. In total, 4 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-20808?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-20808 published?: CVE-2021-20808 was published on 2021-08-26 and last updated on 2026-06-17.

References

Affected products (4)

cpe:2.3:a:sixapart:movable_type:*:*:*:*:premium:*:*:*
cpe:2.3:a:sixapart:movable_type:*:*:*:*:premium_advanced:*:*:*
cpe:2.3:a:sixapart:movable_type:*:*:*:*:-:*:*:*
cpe:2.3:a:sixapart:movable_type:*:*:*:*:advanced:*:*:*

More vulnerabilities in Sixapart Movable Type

CVE-2009-0752 — Critical (CVSS 10.0): Unspecified vulnerability in Movable Type Pro and Community Solution 4.x before 4.24 has unknown impact and attack…
CVE-2026-33088 — Critical (CVSS 9.8): Movable Type provided by Six Apart Ltd. contains an SQL Injection vulnerability which may allow an attacker to execute…
CVE-2026-25776 — Critical (CVSS 9.8): Movable Type provided by Six Apart Ltd. contains a code injection vulnerability which may allow an attacker to execute…
CVE-2022-38078 — Critical (CVSS 9.8): Movable Type XMLRPC API provided by Six Apart Ltd. contains a command injection vulnerability. Sending a specially…
CVE-2021-20837 — Critical (CVSS 9.8): Movable Type 7 r.5002 and earlier (Movable Type 7 Series), Movable Type 6.8.2 and earlier (Movable Type 6 Series),…
CVE-2016-5742 — Critical (CVSS 9.8): SQL injection vulnerability in the XML-RPC interface in Movable Type Pro and Advanced 6.x before 6.1.3 and 6.2.x before…

All CVEs affecting Sixapart Movable Type →

Other CWE-79 (Cross-site Scripting (XSS)) vulnerabilities

CVE-2025-49410 — Critical (CVSS 10.0): Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability in Imran Emu TC…
CVE-2024-47875 — Critical (CVSS 10.0): DOMPurify is a DOM-only, super-fast, uber-tolerant XSS sanitizer for HTML, MathML and SVG. DOMpurify was vulnerable to…
CVE-2024-6886 — Critical (CVSS 10.0): Improper Neutralization of Input During Web Page Generation (XSS or 'Cross-site Scripting') vulnerability in Gitea…
CVE-2023-45144 — Critical (CVSS 10.0): com.xwiki.identity-oauth:identity-oauth-ui is a package to aid in building identity and service providers based on…
CVE-2023-45138 — Critical (CVSS 10.0): Change Request is an pplication allowing users to request changes on a wiki without publishing the changes directly.…
CVE-2022-4361 — Critical (CVSS 10.0): Keycloak, an open-source identity and access management solution, has a cross-site scripting (XSS) vulnerability in the…

Browse all CWE-79 (Cross-site Scripting (XSS)) vulnerabilities →