Security readout for executives and security teams
Plain-English summary
CVE-2021-20813 is a cross-site scripting issue in Movable Type’s Content Data edit screen. An attacker could inject script or HTML through unspecified input. The source bundle does not provide CVSS, detailed prerequisites, or confirmed active exploitation.
Executive priority
Treat this as a targeted platform maintenance issue unless Movable Type administration is exposed to many users. Prioritize upgrade verification for public-facing publishing environments.
Technical view
The vulnerability affects Movable Type 7 r.4903 and earlier, including Movable Type Advanced 7 r.4903 and earlier. It is described as XSS in the Content Data edit screen via unspecified vectors. Technical trigger conditions and privilege requirements are not provided.
Likely exposure
Organizations running affected Movable Type 7 or Movable Type Advanced 7 instances are potentially exposed, especially where content editing workflows are reachable by untrusted or lower-trust users.
Exploitation context
The bundle states remote attackers may inject arbitrary script or HTML. It does not cite public exploitation, and KEV is false, so active exploitation is not established here.
Researcher notes
Key gaps are CVSS, exploit prerequisites, and the unspecified injection vector. Testing should remain non-destructive and focus on version confirmation, UI exposure, and vendor-fixed release comparison.
Mitigation direction
- Check Six Apart’s referenced release guidance for the corrected Movable Type version.
- Upgrade affected Movable Type 7 and Advanced 7 installations beyond r.4903 where vendor guidance confirms remediation.
- Restrict access to administrative content editing interfaces to trusted users.
- Review custom Content Data fields and workflows for untrusted input paths.
Validation and detection
- Inventory Movable Type and Movable Type Advanced versions in production and staging.
- Confirm whether any instance is r.4903 or earlier in the 7 Series.
- Review access controls for the Content Data edit screen.
- Check vendor release notes and JVN advisory for remediation status.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
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CVE-2021-20813 mapping review
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Open ATT&CK lookup- Severity
- Unknown
- CVSS
- Not scored
- Known Exploited
- No
- Published
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS and timeline data
No CVSS vectors or timeline events were available in the normalized CVE source material.
Source materials
- CVE List V5 sourceCVE List V5
- https://movabletype.org/news/2021/08/mt-780-681-released.htmlCVE reference · x_refsource_MISC
- https://jvn.jp/en/jp/JVN97545738/index.htmlCVE reference · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.