Vulnerability report

Active exploitation observed Confirmed confidence In CISA KEV

CVE-2026-39808

FortiSandbox Os command injection

Fortinet / FortiSandbox · 4.4.0 to <= 4.4.8

Watch CVE-2026-39808 Browse KEV feed
Severity
CVSS 9.1 · Critical
Confidence
Confirmed
Exploit status
Observed in sensors
EPSS
47.4%
First observed
12 Jun 2026
Last observed
07 Oct 2026

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2026-39808 is an unauthenticated vulnerability affecting Fortinet FortiSandbox, FortiSandbox PaaS. A improper neutralization of special elements used in an os command ('os command injection') vulnerability in...

Is it exploited?

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

Who is affected?

Fortinet / FortiSandbox 4.4.0 to <= 4.4.8.

What should we do?

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

Overview

FortiSandbox Os command injection

A improper neutralization of special elements used in an os command ('os command injection') vulnerability in Fortinet FortiSandbox 4.4.0 through 4.4.8 may allow attacker to execute unauthorized code or commands via

Fortinet Affected
FortiSandbox
Through 4.4.8
Fortinet Affected
FortiSandbox PaaS
23.4.4374 23.4.4350 23.3.4329 23.1.4245 22.2.4151 22.2.4134 22.1.4113 21.4.4072 21.3.4055
Published
14 Apr 2026
Exploitation Reported
12 Jun 2026
Attack vector
Remote
Complexity
Low
Privileges
None
User interaction
None

Tags

edge nuclei_scanner cisa

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

Previdian

Recorded 12 Jun 2026

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

Active exploitation observed

Previdian sensor

First observed 12 Jun 2026

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

Proof of concept available

Nuclei Templates

Recorded 12 Jun 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.

Learn about Pro API access
Source Added
Previdian Sensors First 2026-06-12 13:59 UTC
The Shadowserver 2026-07-09 00:00 UTC
All CISA Advisories 2026-07-16 12:00 UTC
CISA 2026-07-16 17:00 UTC
CVE 2026-07-16 17:51 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.

205

Attempts observed

48

Unique attacker IPs

22

Attacker countries

AE · AR · CH · CN · DE · ER · FR · HK · ID · IL · IQ · IT · JP · KR · MY · NL · SG · TW · US · UZ · VN · VU

5

Sensors observed

CVE-2026-39808 exploitation attempts over the last 90 days

Daily events observed by Previdian sensors

Updated 09 Oct 2026

0
2
26
0
0
8
26
14
4
30
0
0
2
0
0
4
0
0
2
0
0
0
5
0
0
0
2
1
0
0
0
0
0
0
5
0
0
0
0
0
0
4
2
0
6
0
2
0
3
0
0
0
0
0
19
0
3
2
0
0
0
0
11
0
4
1
0
0
0
0
2
0
0
0
0
0
0
0
8
4
0
0
0
0
0
2
0
1
0
0
12 Jul 30 Jul 17 Aug 4 Sep 9 Oct

First observed 12 Jun 2026 · Last observed 07 Oct 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
27
8
3

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

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.

Learn about Pro API access

Scanner Artifacts

Scanner and exploit-framework references linked to this CVE.

Scanner Reference Detected
Nuclei https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-39808.yaml 01 Jun 2026

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

47.4%

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

Weaknesses

Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection') CWE-78

Recent mention · All CISA Advisories

CISA Adds Three Known Exploited Vulnerabilities to Catalog

CISA has added three new vulnerabilities to its Known Exploited Vulnerabilities (KEV) Catalog, based on evidence of active exploitation. CVE-2026-25089 Fortinet FortiSandbox OS Command Injection Vulnerability   CVE-2026-39808 Fortinet FortiSandbox OS Command Injection...

Read full advisory

All Mentions

Recent mention · All CISA Advisories

CISA Adds Three Known Exploited Vulnerabilities to Catalog

All CISA Advisories · 16 Jul 2026

CISA has added three new vulnerabilities to its Known Exploited Vulnerabilities (KEV) Catalog, based on evidence of active exploitation. CVE-2026-25089 Fortinet FortiSandbox OS Command Injection Vulnerability   CVE-2026-39808 Fortinet FortiSandbox OS Command Injection Vulnerability   CVE-2026-58644 Microsoft SharePoint Deserialization of Untrusted Data Vulnerability These types of vulnerabilities are frequent attack vectors for malicious cyber actors and pose significant risks to the federal enterprise. Binding Operational Directive (BOD) 26-04: Prioritizing Security Updates Based on Risk...

Recent mention · The Hacker News

Attackers Exploit Three Fortinet FortiSandbox Flaws, One Patched Last Week

The Hacker News · 16 Jun 2026

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 24 hours. CVE-2026-39813 (CVSS score: 9.1) refers to a path traversal vulnerability in FortiSandbox JRPC API that could

Potential Proof of Concepts

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

gotr00t0day/CVE-2026-39808

github · Created 2026-10-03 15:50:23 UTC · 0 stars · AI assessment 90%

An unauthenticated OS command injection vulnerability

Fortinet FortiSandbox - Command Injection

nuclei · Created Unknown

Timeline

From disclosure to observed exploitation

  1. 17:51 UTC

    KEV confirmed by CVE

    Exploitation attested by an external source

  2. 17:00 UTC

    Added to CISA KEV

    Listed in the CISA Known Exploited Vulnerabilities catalog

  3. 12:00 UTC

    KEV confirmed by All CISA Advisories

    Exploitation attested by an external source

  4. 00:00 UTC

    KEV confirmed by The Shadowserver

    Exploitation attested by an external source

  5. 14:21 UTC

    Virtual patch available

    Compensating WAF rule available to block exploitation

  6. 14:21 UTC

    Public PoC available

    Public proof-of-concept code published

  7. 13:59 UTC

    Indicators of compromise added (87)

    Indicators of compromise recorded

  8. 13:59 UTC

    Observed by Previdian sensors

    Evidence-backed exploitation signal

  9. 15:34 UTC

    Nuclei template available

    Scanner coverage available

  10. 15:38 UTC

    CVE published

    Vulnerability disclosed publicly

  11. 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-2026-39808

Free JSON includes basic KEV fields 
{
  "cve_id": "CVE-2026-39808",
  "confidence": "Confirmed",
  "cvss_score": 9.1,
  "cvss_estimated": false,
  "epss_score": 0.47362,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": true
  },
  "sensor_telemetry": { "attempts": 205, "sensors": 5 }
}