Arbitrary file upload in Six Apart Ltd. Movable Type Advanced (Software Edition)

CVE-2026-23704

A non-administrative user can upload malicious files. When an administrator or the product accesses that file, an arbitrary script may be executed on the administrator's browser. Note that Movable Type 7 series and 8.4 series, which are End-of-Life (EOL), are affected by the vulnerability as well.

Vulnerability class: Unrestricted File Upload

Published · last modified .

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.0/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:L.

EPSS exploit prediction

EPSS: 0.002 (10.7th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 11th percentile — 10.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-23704: held from 0.002 to 0.002.

EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: +0.000

Affected products

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-23704?
CVE-2026-23704 is a medium-severity vulnerability in Six Apart Ltd. Movable Type Advanced (Software Edition), classified under Unrestricted Upload of File with Dangerous Type. CVSS score: 6.5/10. Published 2026-02-04.
How severe is CVE-2026-23704?
Medium severity. CVSS v3 base score is 6.5 out of 10.