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

This week

CRITICAL 9.8REMOTEUPGRADE

CVE-2026-39813 is a critical-severity flaw (CVSS 9.8) affecting fortisandbox. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

Critical severity
EPSS top 2%: very likely to be exploited
CISA SSVC: automatable with total technical impact
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	22.2% (top 2%)
CISA exploited list	No
Weakness	CWE-24
Published	2026-04-14
Last modified	2026-10-26

Publisher (CNA): Fortinet, Inc. · Vendor: fortinet

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-14 16:16 UTCPublished CVE record published
2026-10-26 21:10 UTCUpdated Record last modified

fortinet fortisandbox UPGRADE

Affected: >= 4.4.0 and < 4.4.9 · >= 5.0.0 and < 5.0.6

Fixed in: 4.4.9, 5.0.6

Safe to downgrade to: a release before 4.4.0

1. Check installed version

apt-cache policy fortisandbox || rpm -q fortisandbox || fortisandbox --version

2. UPGRADE to 4.4.9 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade fortisandbox

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade fortisandbox

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 4.4.0 (Debian / Ubuntu)

apt-cache madison fortisandbox sudo apt install fortisandbox=<VERSION_BEFORE_4.4.0> sudo apt-mark hold fortisandbox

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list fortisandbox sudo dnf downgrade fortisandbox-<VERSION_BEFORE_4.4.0> sudo dnf versionlock add fortisandbox

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

GitHub PoC: 0xBlackash/CVE-2026-39813 (0 stars)
GitHub PoC: HORKimhab/CVE-2026-39813 (0 stars)

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-39813?

fortisandbox: upgrade to 4.4.9, 5.0.6. Exact commands for each OS are on this page.

Is CVE-2026-39813 being exploited?

CVE-2026-39813 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-39813 affect?

CVE-2026-39813 affects fortisandbox. Severity is critical (CVSS 9.8). 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.

How urgent is CVE-2026-39813?

Priority 67/100. Critical severity; EPSS top 2%: very likely to be exploited; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action

Software pages

Fortinet vulnerabilities

Related CVEs

CVE-2026-25691 MEDIUM 6.7 UPGRADE DOWNGRADE A improper limitation of a pathname to a restricted directory ('path traversal') vulnerability in Fortinet For
CVE-2026-39812 MEDIUM 4.8 UPGRADE UPGRADE A improper neutralization of input during web page generation ('cross-site scripting') vulnerability in Fortin
CVE-2026-39808 CRITICAL 9.8 EXPLOITED UPGRADE Fortinet FortiSandbox OS Command Injection Vulnerability
CVE-2026-27316 LOW 2.7 UPGRADE DOWNGRADE A insufficiently protected credentials vulnerability in Fortinet FortiSandbox 5.0.0 through 5.0.5, FortiSandbo
CVE-2026-26083 CRITICAL 9.8 UPGRADE UPGRADE A missing authorization vulnerability in Fortinet FortiSandbox 5.0.0 through 5.0.1, FortiSandbox 4.4.0 through

References

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