What is CVE-2026-39813?

CVE-2026-39813 is a critical-severity vulnerability in Fortinet Fortisandbox, classified under CWE-24. CVSS score: 9.8/10. Published 2026-04-14.

How severe is CVE-2026-39813?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Is CVE-2026-39813 known to be exploited?

2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Vulnerability in Fortinet Fortisandbox

CVE-2026-39813

A path traversal: '../filedir' vulnerability in Fortinet FortiSandbox 5.0.0 through 5.0.5, FortiSandbox 4.4.0 through 4.4.8 may allow attacker to escalation of privilege via specially crafted HTTP requests.

Published 2026-04-14 · last modified 2026-06-18.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.007 (53.0th percentile), scored 2026-10-18.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 53rd percentile — 53.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.222 · newest: 0.007 · change: -0.215

Affected products

Fortinet Fortisandbox — versions 5.0.0, 4.4.0
Fortinet Fortisandbox Cloud — versions 24.1, 23.4, 5.0.4

Weakness classification (CWE)

CWE-24

Public proof-of-concept exploits

References

fortiguard.fortinet.com/psirt/FG-IR-26-112 (Vendor Advisory)

Frequently asked questions

What is CVE-2026-39813?: CVE-2026-39813 is a critical-severity vulnerability in Fortinet Fortisandbox, classified under CWE-24. CVSS score: 9.8/10. Published 2026-04-14.
How severe is CVE-2026-39813?: Critical severity. CVSS v3 base score is 9.8 out of 10.
Is CVE-2026-39813 known to be exploited?: 2 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.