---
id: "CVE-2026-39813"
kind: "vulnerability"
aliases: ["CVE-2026-39813"]
title: "Fortinet FortiSandbox: path traversal lets unauthenticated attackers read arbitrary files"
severity: "critical"
cvss: 9.8
epss: 0.0072
exploited: false
status: "open"
category: "vendor"
products: [{"name": "fortinet fortisandbox", "fixed": ["4.4.9"], "affected": ">= 4.4.0, < 4.4.9", "ecosystem": "vendor"}, {"name": "fortinet fortisandbox", "fixed": ["5.0.6"], "affected": ">= 5.0.0, < 5.0.6", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["cloudflare", "fortinet", "fortisandbox", "lab-disclosure", "network", "security-appliance", "vendor"]
not_affected_if: ["not-internet-exposed", "patched-version"]
published_at: "2026-04-14T16:16:45+00:00"
first_seen_at: "2026-10-24T18:43:45+00:00"
updated_at: "2026-10-25T12:38:49+00:00"
sources: [{"source": "lab", "url": "https://developers.cloudflare.com/changelog/post/2026-07-01-waf-release/", "first_seen_at": "2026-10-24T18:43:45+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-39813", "first_seen_at": "2026-10-24T18:53:56+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-39813", "first_seen_at": "2026-10-25T12:38:49+00:00"}]
---

# Fortinet FortiSandbox: path traversal lets unauthenticated attackers read arbitrary files

FortiSandbox 4.4.0 through 4.4.8 and 5.0.0 through 5.0.5 contain a path traversal flaw in how user-supplied paths are validated. A remote attacker without an account can read arbitrary files from the appliance filesystem.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:fortinet fortisandbox affected >= 4.4.0, < 4.4.9 fixed 4.4.9
- vendor:fortinet fortisandbox affected >= 5.0.0, < 5.0.6 fixed 5.0.6

## How to check

- Check the FortiSandbox firmware version in the admin GUI or with `get system status` on the CLI.
- Check whether the appliance is reachable from the internet or untrusted networks.
- Review the Cloudflare changelog for WAF rule coverage if the appliance is behind Cloudflare.

## Fix

- Upgrade FortiSandbox 4.4.x to `4.4.9`.
- Upgrade FortiSandbox 5.0.x to `5.0.6`.
- Restrict management and web access to trusted networks until patched.

## Timeline

- 2026-10-24T18:43:45+00:00 lab https://developers.cloudflare.com/changelog/post/2026-07-01-waf-release/ — Cloudflare: WAF Release - 2026-07-01 · Changelog
- 2026-10-24T18:53:56+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-39813
- 2026-10-25T12:38:49+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-39813

## Documents

- [advisory] Cloudflare: WAF Release - 2026-07-01 · Changelog https://developers.cloudflare.com/changelog/post/2026-07-01-waf-release/

## From the sources

WAF Release - 2026-07-01 · Changelog

# Changelog

New updates and improvements at Cloudflare.

July 1, 2026

## WAF Release - 2026-07-01

This release adds targeted coverage for a path traversal flaw in Fortinet FortiSandbox (CVE-2026-39813) and transitions the Anomaly:Header:User-Agent - Fake Bing or MSN Bot rule action from Block to Disabled.

Key Findings

- CVE-2026-39813: A path traversal vulnerability in Fortinet FortiSandbox allows remote, unauthenticated attackers to read arbitrary files from the underlying filesystem due to insufficient validation of user-supplied input paths.

| Ruleset | Rule ID | Legacy Rule ID | Description | Previous Action | New Action | Comments |
| --- | --- | --- | --- | --- | --- | --- |
| Cloudflare Managed Ruleset | ...d84c92c9 | N/A | Fortinet FortiSandbox - Path Traversal - CVE:CVE-2026-39813 | Log | Block | This is a new detection. |
| Cloudflare Managed Ruleset | ...c12cf9c8 | N/A | Anomaly:Header:User-Agent - Fake Bing or MSN Bot | Enabled | Disabled | We are changing the action for this rule from BLOCK to Disabled |

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_