Vulnerability report

Active exploitation observed Confirmed confidence Not in CISA KEV

CVE-2026-39813

FortiSandbox Path Traversal

Fortinet / FortiSandbox · 5.0.0 to <= 5.0.5

Watch CVE-2026-39813 Browse KEV feed
Severity
CVSS 9.1 · Critical
Confidence
Confirmed
Exploit status
Observed in sensors
EPSS
0.7%
First observed
15 Jun 2026
Last observed
05 Aug 2026

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2026-39813 is an unauthenticated vulnerability affecting Fortinet FortiSandbox, FortiSandbox Cloud. A path traversal: '../filedir' vulnerability in Fortinet FortiSandbox 5.0.0 through 5.0.5, FortiSandbox 4.4.0...

Is it exploited?

Yes. Previdian sensors observed exploitation attempts with confirmed confidence. Also confirmed by third-party sources.

Who is affected?

Fortinet / FortiSandbox 5.0.0 to <= 5.0.5.

What should we do?

Patch immediately, validate internet-facing exposure, and monitor for matching requests.

Overview

FortiSandbox Path Traversal

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.

Fortinet Affected
FortiSandbox
Through 5.0.5 Through 4.4.8
Fortinet Affected
FortiSandbox Cloud
24.1 23.4 Through 5.0.5
Published
14 Apr 2026
Exploited Since
15 Jun 2026
Attack vector
Remote
Complexity
Low
Privileges
None
User interaction
None

Tags

edge

CVE References

Exploitation evidence

Why Previdian marks this CVE as exploited

Third-party attestation and first-party sensor observation are shown separately so teams can judge the evidence chain.

Exploited in the wild

Defused Cyber

Recorded 16 Jun 2026

Previdian independently recorded this as exploited after first seeing it in honeypot sensors.

Active exploitation observed

Previdian sensor

First observed 15 Jun 2026

Previdian first observed exploitation attempts targeting this vulnerability in our honeypot sensors.

Proof of concept available

GitHub

Recorded 21 Apr 2026

Public scanner or PoC coverage increases practical exploitability.

Known exploited vulnerability sources

Per-source evidence links for KEV attestations are available through the Previdian Pro API.

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Source Added
Defused Cyber First 2026-06-16 15:17 UTC
Previdian Sensors 2026-06-15 12:48 UTC

Operational indicators for this CVE are listed under Detection.

Sensor telemetry

First-party evidence of exploitation activity

Previdian sensors recorded exploitation attempts targeting this vulnerability. The cards and chart show volume, unique attackers, and daily activity.

4

Attempts observed

3

Unique attacker IPs

2

Attacker countries

CN · TH

1

Sensors observed

CVE-2026-39813 exploitation attempts over the last 73 days

Daily events observed by Previdian sensors

Updated 10 Oct 2026

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30 Jul 14 Aug 29 Aug 13 Sep 10 Oct

First observed 15 Jun 2026 · Last observed 05 Aug 2026

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Detection

Operational artifacts and observed signals

Make the evidence actionable in scanner, SOC, and edge-control workflows.

Observed signals

Request targets
User-Agents
Callback hosts
0
0
0

Request targets and User-Agents available in Pro. Callback host details available in Enterprise.

Scanner coverage

No scanner integrations recorded yet.

Virtual patch status

Previdian virtual patch guidance is available for this CVE.

AWS WAF Cloudflare ModSecurity

Attacker IP Indicators

Attacker IP indicators observed · available in Pro and Enterprise.

Sensor-derived attacker IP indicators are available to Pro and Enterprise accounts under Detection and through the Pro API.

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Virtual Patch Detail

Compensating WAF rules for this CVE.

Available

Enterprise feature. Virtual patch rule content and deployable vendor exports (ModSecurity, Cloudflare, AWS WAF) are available to Previdian Enterprise users.

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Risk and context

Severity, weaknesses, and research context

CVSS v3.1

9.1 Critical

Potential damage if exploited. Separate from whether attackers are using it.

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

0.7%

Estimated chance of exploitation in the next 30 days. Previdian's warning comes from evidence, not this score.

Weaknesses

Path Traversal: '../filedir' CWE-24

Recent mention · The Hacker News

Attackers Exploit Three Fortinet FortiSandbox Flaws, One Patched Last Week

Bad actors are exploiting multiple security vulnerabilities in Fortinet FortiSandbox, according to threat intelligence firm Defused Cyber. In a post shared on X, the company said it has observed exploitation of CVE-2026-39813, CVE-2026-39808, and CVE-2026-25089 over the past...

Read full advisory

Potential Proof of Concepts

These PoCs are unverified and could contain malware. Use at your own risk.

CVE-2026-39813 Deep Dive Path Traversal Authentication Bypass in FortiSandbox JRPC API

public · Created 2026-04-21 17:10:00 UTC

Timeline

From disclosure to observed exploitation

  1. 14:21 UTC

    Virtual patch available

    Compensating WAF rule available to block exploitation

  2. 15:17 UTC

    Added to Previdian KEV Feed

    High-confidence, third-party attested exploitation

  3. 12:48 UTC

    Indicators of compromise added (15)

    Indicators of compromise recorded

  4. 12:48 UTC

    Observed by Previdian sensors

    Evidence-backed exploitation signal

  5. 17:10 UTC

    Public PoC available

    Public proof-of-concept code published

  6. 15:38 UTC

    CVE published

    Vulnerability disclosed publicly

  7. 15:24 UTC

    CVE ID reserved

    Identifier reserved by the CNA

Pro API

Automate this intelligence

Confidence, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.

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  • Evidence confidence and provenance
  • First-party sensor telemetry
  • PoC and scanner references
  • Affected versions and enrichment
  • Automation-ready JSON delivery

GET /api/v2/pro/kevs/CVE-2026-39813

Free JSON includes basic KEV fields 
{
  "cve_id": "CVE-2026-39813",
  "confidence": "Confirmed",
  "cvss_score": 9.1,
  "cvss_estimated": false,
  "epss_score": 0.0072,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": true
  },
  "sensor_telemetry": { "attempts": 4, "sensors": 1 }
}