Authentication Bypass via Path Traversal in FortiSandbox JRPC API
CVE-2026-39813 is a critical path traversal vulnerability in the Fortinet FortiSandbox JRPC API affecting FortiSandbox 4.4.0 through 4.4.8 and 5.0.0 through 5.0.5. The flaw is described as a '../filedir' path traversal issue and can be triggered via specially crafted HTTP requests to the JRPC API. According to the provided content, a remote unauthenticated attacker can exploit the vulnerable API to bypass authentication controls and escalate privileges on the appliance. Multiple sources in the content characterize the issue as pre-authentication and network exploitable, with no user interaction required.
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Impact, mitigation & remediation
What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
Impact
What an attacker gets, and what they’ve been doing with it.
Mitigation
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Remediation
Patch, then assume compromise.
Exploits
1 valid exploit after Mallory filtered fakes, detection scripts, and README-only repos (2 hidden).
This repository is a small exploit repo with 3 files: a Python PoC, a Nuclei template, and a README. Because it includes a Nuclei template, it is part of a framework; the main exploit logic is captured in CVE-2026-39808.yaml, while the Python script provides a standalone implementation of the same attack chain. The exploit targets Fortinet FortiSandbox and chains an unauthenticated access check against /api/v1/system/firmware (described as CVE-2026-39813 auth bypass) with a command injection in /fortisandbox/job-detail/tracer-behavior via the jid parameter (CVE-2026-39808). The injected command writes output to /web/ng/out.txt, which is then retrieved from /ng/out.txt to confirm root-level execution. The Nuclei template fingerprints the login page, extracts version information, triggers a benign id payload, and verifies success by matching uid=0/gid=0 in the output. Overall, this is a real unauthenticated web RCE PoC for vulnerable FortiSandbox versions, providing root command execution and simple output exfiltration through a web-accessible file.
Affected products & vendors
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Recent activity
72 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
An authentication bypass vulnerability in the FortiSandbox API that allows attackers to bypass login controls and gain access to administrative functions.
A critical path-traversal vulnerability in Fortinet FortiSandbox that researchers observed being exploited.
A critical pre-authentication Fortinet FortiSandbox vulnerability that was reportedly exploited in the wild. It requires no login to exploit and is among flaws enabling code execution on the appliance.
A critical path traversal vulnerability in the FortiSandbox JRPC API that can allow unauthenticated attackers to bypass authentication via crafted HTTP requests.
The version that knows your environment.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.