Fortinet FortiSandbox: OS command injection via unauthenticated HTTP requests

Summary

An improper neutralization of special elements in the web UI of FortiSandbox, FortiSandbox Cloud and FortiSandbox PaaS allows an unauthenticated attacker to execute unauthorized OS commands. The attacker only needs to send specifically crafted HTTP requests; Fortinet describes it as a second-order injection via JSON input on the "start vnc" feature. The CVSS score is 9.8 (critical), and CISA has added the flaw to its Known Exploited Vulnerabilities catalog, so exploitation in the wild is treated as confirmed, although Fortinet has not confirmed it.

Affected

• FortiSandbox 5.0.0 through 5.0.5
• FortiSandbox 4.4.0 through 4.4.8
• FortiSandbox 4.2 (all versions, as listed in the CVE record; Fortinet's PSIRT table does not list this branch)
• FortiSandbox Cloud 5.0.4 through 5.0.5
• FortiSandbox PaaS 5.0.4 through 5.0.5
• Not affected according to Fortinet: FortiSandbox 5.2, FortiSandbox Cloud 5.2 and 4.4, FortiSandbox PaaS 5.2, 4.4 and 23.4

Fixed in

• FortiSandbox 5.0: upgrade to 5.0.6 or later
• FortiSandbox 4.4: upgrade to 4.4.9 or later
• FortiSandbox Cloud and PaaS: the provider applies the fix; verify that the June 9, 2026 patch (FG-IR-26-141) is in place
• FortiSandbox 4.2: no fix documented; unknown

Workaround

• No official Fortinet workaround; Fortinet lists upgrades as the only solution.
• Third-party guidance: restrict access to the management interface to trusted internal addresses (not confirmed by Fortinet).
• For systems that cannot be upgraded immediately, restrict management access and place compensating controls in front of the interface.

Exploitation

• CISA KEV: known exploited, added July 16, 2026, with a July 19, 2026 deadline for federal agencies.
• Fortinet has not confirmed exploitation; the PSIRT records no prior exploitation.
• Reports of exploitation attempts from mid-June come from secondary sources and could not be verified.
• Public proof of concept: unknown.

Our recommendation

• Identify all FortiSandbox, FortiSandbox Cloud and PaaS instances and their versions.
• Upgrade 5.0 systems to 5.0.6 or later and 4.4 systems to 4.4.9 or later; prioritise systems reachable from the internet.
• For cloud and PaaS services, confirm with the provider that the fix is applied.
• Treat 4.2 systems as unpatched: ask Fortinet for a fixed version or plan a migration, and isolate the management interface in the meantime.
• Review web UI access logs for unusual requests and check the appliance for unexpected outbound connections or signs of compromise before assuming the patch is sufficient.

Public exploits iAttack code is publicly available (PoC on GitHub, Metasploit or Exploit-DB).

Links to third-party sites, not checked by us – exploit code can contain malware. Only use it in isolated test environments.

• Proof of concept on GitHub (2 repositories) iAttack code is publicly available (PoC on GitHub, Metasploit or Exploit-DB).
  HORKimhab/CVE-2026-25089 · 0xBlackash/CVE-2026-25089

Research sources

• Fortinet PSIRT FG-IR-26-141 fortiguard.fortinet.com
• CISA Known Exploited Vulnerabilities Catalog www.cisa.gov
• UpGuard CVE-2026-25089 www.upguard.com
• CSA Research Note: FortiSandbox triple CVE exploitation labs.cloudsecurityalliance.org
• CSA Singapore Alert AL-2026-073 www.csa.gov.sg
• GovInfoSecurity: CISA adds FortiSandbox bugs to KEV www.govinfosecurity.com
• Linkloot: FortiSandbox CISA KEV July 19 deadline linkloot.io

Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 31 Oct 2026, 19:53.