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CVE-2021-20809

• Severity: medium (CVSS 6.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.9% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2021-08-26 · updated 2026-06-17
• Weakness: CWE-79

Description

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.

Affected products

• Six Apart Ltd. Movable Type: through 1.44; from 6.0 through 6.8.0; from 7.0 before 7.8.0 — fixed in 7.8.0

How to fix

Upgrade to a fixed version: Six Apart Ltd. Movable Type 7.8.0. Check the vendor advisory for mitigations.

References

• https://jvn.jp/en/jp/JVN97545738/index.html
• https://movabletype.org/news/2021/08/mt-780-681-released.html
• https://jvn.jp/en/jp/JVN97545738/index.html
• https://movabletype.org/news/2021/08/mt-780-681-released.html

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