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Fortinet FortiSandbox, JRPC API OS command injection (CVSS 9.8); actively exploited
cve
· CVE-2026-39808
Coverage
1
first 2026-06-12 → last 2026-10-11
Latest activity
2026-06-17
Defused reports exploitation of three pre-auth FortiSandbox flaws and CISA lists two in KEV; upgrading to…
Peak priority
high
1 high
Targets
public-sector
sectors: public-sector, technology, defense · regions: europe
Sources cited
8
6 hosts
Action items (1)
Do-now tasks recorded on the entries about CVE-2026-39808, newest first. Check the date before acting on an older one.
Upgrade every FortiSandbox on the 5.0, 4.4 or 4.2 branch to 5.0.6 or 4.4.9, which fixes all three flaws Defused reports exploited (CVE-2026-25089, CVE-2026-39808, CVE-2026-39813), and confirm the web UI and JRPC API answer only from the management network.
trending-vulnerabilitiesDefused reports exploitation of three pre-auth FortiSandbox flaws and CISA lists two in KEV; upgrading to 5.0.6 or 4.4.9 fixes all three
1 technique observed across 1 entry about this entity, derived from entry metadata and body evidence, never asserted without a published entry behind it · pinned to MITRE ATT&CK v20.0 · compare on the matrix · Navigator layer (JSON)
Initial AccessExploit Public-Facing Application
Initial Access TA0001
T1190Exploit Public-Facing Application×1
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network. The weakness in the system can be a software bug, a temporary glitch, or a misconfiguration.
Fortinet patched CVE-2026-25089 (CWE-78) on 2026-06-09: the FortiSandbox web interface's "start vnc" feature passes attacker-controlled JSON input to an OS command, a second-order injection that "may allow an unauthenticated attacker to execute unauthorized commands via specifically crafted HTTP requests" (Fortinet PSIRT FG-IR-26-141, 2026-06-09). Affected are FortiSandbox 5.0.0 through 5.0.5 and 4.4.0 through 4.4.8 plus FortiSandbox Cloud and PaaS 5.0.4 through 5.0.5; the fix is 5.0.6 or 4.4.9, and the 5.2 branch is not affected (Fortinet PSIRT FG-IR-26-141, 2026-06-09). CCB Belgium urged immediate patching and warned that a public proof-of-concept raises the likelihood of exploitation (CCB Belgium, 2026-06-11).
Help Net Security describes FortiSandbox as a platform that other Fortinet security products depend on for threat verdicts to enforce blocking decisions and trigger automated responses (Help Net Security, 2026-06-16).
Contradiction: CCB Belgium says a publicly available proof-of-concept exploit raises the likelihood of exploitation (CCB Belgium, 2026-06-11), while Security Affairs reports that a working exploit for CVE-2026-25089 has not been publicly disclosed and that the exploit seen in attacks appears AI-assisted and bugged (Security Affairs, 2026-06-16).
may allow an unauthenticated attacker to execute unauthorized commands via specifically crafted HTTP requests
Threat-intelligence firm Defused Cyber reported active exploitation of three FortiSandbox flaws within a 24-hour window: CVE-2026-39813 (CVSS 9.1), a JRPC API path traversal that allows authentication bypass, and CVE-2026-39808 (CVSS 9.8), an OS command injection, both patched in April 2026, and CVE-2026-25089, the web UI command injection patched on 2026-06-09 (Security Affairs, 2026-06-16). Defused researchers speculate that the CVE-2026-25089 exploit was built with AI assistance and is bugged, yet attackers are still using it against unpatched systems (Security Affairs, 2026-06-16).
Help Net Security describes FortiSandbox as a platform that other Fortinet security products depend on for threat verdicts to enforce blocking decisions and trigger automated responses, and notes that Fortinet had not yet confirmed in-the-wild exploitation (Help Net Security, 2026-06-16).
The earlier main text said no in-the-wild exploitation was reported, treated a public proof-of-concept as established and carried a table of unrelated CVEs. Defused reported exploitation of all three flaws, which Fortinet had not confirmed (Help Net Security, 2026-06-16), and Fortinet's advisories list them as not known exploited (Fortinet PSIRT FG-IR-26-141, 2026-06-09) (Fortinet PSIRT FG-IR-26-112, 2026-04-14) (Fortinet PSIRT FG-IR-26-100, 2026-04-14). CISA added CVE-2026-25089 and CVE-2026-39808 to its KEV catalog on 2026-07-16 (CISA KEV catalog, 2026-07-16). Fortinet's advisories give the affected and fixed versions. For CVE-2026-25089 and CVE-2026-39813, 5.0.0 through 5.0.5 and 4.4.0 through 4.4.8 are affected, 5.0.6 or 4.4.9 fixes them and 5.2 is not affected (Fortinet PSIRT FG-IR-26-141, 2026-06-09) (Fortinet PSIRT FG-IR-26-112, 2026-04-14). For CVE-2026-39808, 4.4.0 through 4.4.8 is affected, 4.4.9 fixes it and 5.0 is not affected (Fortinet PSIRT FG-IR-26-100, 2026-04-14). Sources disagree on whether a public proof-of-concept exists (CCB Belgium, 2026-06-11) (Security Affairs, 2026-06-16). The 2026-06-17 text said FortiSandbox feeds verdicts to FortiGate, FortiMail, FortiProxy and FortiClient and that a compromised sandbox can suppress detection across that stack, while the cited report says only that other Fortinet security products depend on its verdicts (Help Net Security, 2026-06-16). CVE-2026-39813 was listed at CVSS 9.1 next to 9.8 for the other two. Fortinet gives all three the same vector, which scores 9.8 before the temporal adjustment behind the 9.1 on its advisories (Fortinet PSIRT FG-IR-26-112, 2026-04-14).
Contradiction: NCSC-NL says Fortinet fixed the flaw in FortiSandbox versions 4.2 through 5.0.5 (NCSC-NL, 2026-06-11), while Fortinet's advisory lists 4.4.0 through 4.4.8 and 5.0.0 through 5.0.5 as affected and does not mention 4.2 (Fortinet PSIRT FG-IR-26-141, 2026-06-09). Operators still on 4.2 should assume exposure and move to 4.4.9 or later.