If a malformed data is input to the affected product, a CSV file downloaded from the affected product may contain such malformed data. When a victim user download and open such a CSV file, the embedded code may be executed in the user's environment. Note that Movable Type 7 series and 8.4 series, which are End-of-Life (EOL), are affected by the vulnerability as well.

If a malformed data is input to the affected product, a CSV file downloaded from the affected product may contain such malformed data. When a victim user download and open such a CSV file, the embedded code may be executed in the user's environment. Note that Movable Type 7 series and 8.4 series, which are End-of-Life (EOL), are affected by the vulnerability as well.

Movable Type provided by Six Apart Ltd. contains multiple vulnerabilities listed below.<ul><li>Stored cross-site scripting vulnerability in Edit Comment (CWE-79) - CVE-2026-21393</li><li>Stored cross-site scripting vulnerability in Export Sites (CWE-79) - CVE-2026-22875</li><li>Unrestricted upload of file with dangerous type (CWE-434) - CVE-2026-23704</li><li>Improper neutralization of formula elements in a CSV file (CWE-1236) - CVE-2026-24447</li></ul>CVE-2026-21393, CVE-2026-22875 Kentaro Ishii of GMO Cybersecurity by Ierae, Inc. reported these vulnerabilities to IPA. CVE-2026-23704, CVE-2026-24447 Six Apart Ltd. reported these vulnerabilities to JPCERT/CC to notify users of the solutions through JVN. JPCERT/CC and Six Apart Ltd. coordinated under the Information Security Early Warning Partnership.