# CVE-2026-39813 — Fortinet FortiSandbox

> As of 2026-06-18, CVE-2026-39813 is a CRITICAL-severity vulnerability in Fortinet FortiSandbox, CVSS v3.1 9.1, EPSS 0.7% (52.5th percentile). Threadlinqs Intelligence links 6 tracked threat campaigns to CVE-2026-39813, most recently “Critical FortiSandbox GUI Authentication Bypass (CVE-2026-107656)”.

**Last updated:** 2026-06-18

## What is 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.

The record classifies CVE-2026-39813 under weakness class [CWE-24](https://cwe.mitre.org/data/definitions/24.html). Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs no user interaction, and has high impact on confidentiality, integrity, availability. 2 affected-product entries are recorded, across 1 vendor, listed below. The identifier was first published 183 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 9.1 — CRITICAL (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C`)
- **EPSS (FIRST):** 0.7% probability of exploitation in the next 30 days, higher than 52.5% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 8.7/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-04-14, last modified 2026-06-18

## Is CVE-2026-39813 being exploited?

Weaponised exploit code for CVE-2026-39813 is publicly available. 2 public proof-of-concept repositories are tracked for this identifier. It currently carries a trending score of 36 in the Threadlinqs vulnerability feed.

- [0xBlackash/CVE-2026-39813](https://github.com/0xBlackash/CVE-2026-39813) (github)
- [HORKimhab/CVE-2026-39813](https://github.com/HORKimhab/CVE-2026-39813) (github)

## Affected products and versions

- [Fortinet](https://intel.threadlinqs.com/vendors/fortinet): FortiSandbox, FortiSandbox Cloud

## How to fix CVE-2026-39813

No vendor patch reference has been recorded for CVE-2026-39813 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-39813

6 tracked threats in the Threadlinqs corpus reference CVE-2026-39813, either in the campaign’s CVE list or as an indicator on the campaign record.

- [Critical FortiSandbox GUI Authentication Bypass (CVE-2026-107656)](https://intel.threadlinqs.com/threat/TL-2026-3433) — CRITICAL · 2026-10-13
- [CISA KEV: Fortinet FortiSandbox OS Command Injection Vulnerabilities Exploited (CVE-2026-39808, CVE-2026-25089)](https://intel.threadlinqs.com/threat/TL-2026-1432) — CRITICAL · 2026-07-17
- [CISA Orders Federal Agencies to Patch Exploited Fortinet FortiSandbox Command Injection Flaws (CVE-2026-39808, CVE-2026-25089, CVE-2026-39813)](https://intel.threadlinqs.com/threat/TL-2026-1433) — CRITICAL · 2026-07-17
- [CISA Orders Patch of Actively Exploited Critical FortiSandbox OS Command Injection Flaws (CVE-2026-39808, CVE-2026-25089, CVE-2026-39813)](https://intel.threadlinqs.com/threat/TL-2026-1447) — CRITICAL · 2026-07-17
- [FortiSandbox VNC Server Exposure Allows Unauthenticated Access to Scanning VMs (CVE-2026-59835)](https://intel.threadlinqs.com/threat/TL-2026-1319) — HIGH · 2026-07-14
- [FortiSandbox Unauthenticated RCE Chain: JRPC API Path-Traversal Auth Bypass and OS Command Injection (CVE-2026-39813, CVE-2026-39808, CVE-2026-25089)](https://intel.threadlinqs.com/threat/TL-2026-0823) — CRITICAL · 2026-06-16

## Sources

Enriched from CVE.org, FIRST EPSS, GitHub Security Advisories, public proof-of-concept repositories. Last verified by Threadlinqs on 2026-10-10.

**Other references**

- [fortiguard.fortinet.com](https://fortiguard.fortinet.com/psirt/FG-IR-26-112)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-39813
Full detection coverage and IOCs for threats exploiting CVE-2026-39813 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp