What is CVE-2026-100389?

CVE-2026-100389 is a high-severity vulnerability in Gestsup, classified under Unrestricted Upload of File with Dangerous Type. CVSS score: 8.1/10. Published 2026-09-25.

How severe is CVE-2026-100389?

High severity. CVSS v3 base score is 8.1 out of 10.

Arbitrary file upload in Gestsup

CVE-2026-100389

GestSup versions before 3.2.62 contain a remote code execution vulnerability in the basic IMAP connector's attachment handling that fails to skip blocked file extensions. Unauthenticated attackers can send emails with PHP attachments to monitored mailboxes, which are written to the web-accessible upload/ticket directory and executed when accessed.

Vulnerability class: Unrestricted File Upload

Published 2026-09-25 · last modified 2026-09-30.

CVSS v3 metric

CVSS v3 base score 8.1 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.006 (48.0th percentile), scored 2026-11-10.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 48th percentile — 48.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.006 · newest: 0.006 · change: 0.000

Affected products

Gestsup

Weakness classification (CWE)

CWE-434 — Unrestricted Upload of File with Dangerous Type

References

gestsup.fr/index.php (release-notes)
gestsup.fr/index.php (product)
VulnCheck Advisory: GestSup before 3.2.61 Remote Code Execution via IMAP Attachment (third-party-advisory)
blog.spiizn.xyz/articles/remote-code-execution-turning-a-ticket-into-a-new-issu… (technical-description, exploit)

Frequently asked questions

What is CVE-2026-100389?: CVE-2026-100389 is a high-severity vulnerability in Gestsup, classified under Unrestricted Upload of File with Dangerous Type. CVSS score: 8.1/10. Published 2026-09-25.
How severe is CVE-2026-100389?: High severity. CVSS v3 base score is 8.1 out of 10.