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CVE-2026-100389 – Unauthenticated Remote Code Execution via IMAP Attachment – GestSup before 3.2.61

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Summary

CVE-2026-100389 is a critical unrestricted file upload vulnerability (CWE-434) in GestSup’s IMAP connector, affecting all versions prior to 3.2.61. The connector fails to block dangerous file extensions when importing email attachments into monitored mailboxes, allowing an unauthenticated attacker to achieve remote code execution on the underlying web server. The issue carries a CVSS score of 9.2 (Critical).

Technical details

  • Root cause: GestSup’s basic IMAP connector, when processing incoming email attachments for ticket creation, fails to skip or reject blocked/dangerous file extensions such as .php.
  • Trigger conditions: An attacker sends an email containing a malicious PHP attachment to a mailbox that GestSup monitors via its IMAP connector; no authentication to the GestSup application itself is required.
  • Attack vector: Network — the malicious attachment is delivered via email (IMAP ingestion) and does not require any interaction with the GestSup web interface.
  • Impact: The uploaded PHP file is written into the web-accessible upload/ticket directory. Once stored there, an attacker can access it directly via HTTP, causing the web server to execute the attacker-supplied PHP code — resulting in full remote code execution with complete loss of confidentiality, integrity, and availability.

Affected software

  • GestSup versions prior to 3.2.61 (all versions before 3.2.61 are vulnerable)

Severity

  • CVSS Score: 9.2 (Critical)
  • CVSS Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate: Upgrade GestSup to version 3.2.61 or later, which fixes the file extension validation in the IMAP attachment handler.
  • If patching is not immediately possible:
    • Disable or restrict the IMAP connector/mailbox monitoring feature until the upgrade can be applied.
    • Configure the web server to disable script execution (e.g., PHP interpretation) within the upload/ticket directory used to store email attachments.
    • Deploy a web application firewall or mail-gateway filtering rule to strip or block executable attachment types (e.g., .php, .phtml) before they reach monitored mailboxes.
    • Restrict direct HTTP access to the upload/ticket directory where attachments are stored.

References

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