CVE-2026-39812: A improper neutralization of input during web page generation ('cross-site scripting') vulnerability in Fortin

Routine

MEDIUM 4.8UPGRADEUPGRADE

CVE-2026-39812 is a medium-severity flaw (CVSS 4.8) affecting fortisandbox, fortisandbox cloud. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A improper neutralization of input during web page generation ('cross-site scripting') vulnerability in Fortinet FortiSandbox 5.0.0 through 5.0.5, FortiSandbox 4.4.0 through 4.4.8, FortiSandbox 4.2 all versions, FortiSandbox PaaS 5.0.0 through 5.0.5, FortiSandbox PaaS 4.4.0 through 4.4.8, FortiSandbox PaaS 4.2 all versions may allow attacker to execute unauthorized code or commands via <insert attack vector here>

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	4.8 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	High
User interaction	Required
EPSS exploit chance	0.2% (top 91%)
CISA exploited list	No
Weakness	CWE-79
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 22:10 UTCUpdated Record last modified

fortinet fortisandbox UPGRADE

Affected: >= 4.2.0 and <= 4.2.8 · >= 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 4.2.0

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 4.2.0 (Debian / Ubuntu)

apt-cache madison fortisandbox sudo apt install fortisandbox=<VERSION_BEFORE_4.2.0> 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_4.2.0> 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.

fortinet fortisandbox cloud UPGRADE

Affected: >= 22.2.4134 and <= 23.1.4260 · >= 23.3.4329 and <= 24.1.4436 · 5.0.4 · 5.0.5

Fixed in: newer than 24.1.4436

Safe to downgrade to: a release before 5.0.4

1. Check installed version

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

2. UPGRADE to newer than 24.1.4436 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade fortisandbox-cloud

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 5.0.4 (Debian / Ubuntu)

apt-cache madison fortisandbox-cloud sudo apt install fortisandbox-cloud=<VERSION_BEFORE_5.0.4> sudo apt-mark hold fortisandbox-cloud

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

dnf --showduplicates list fortisandbox-cloud sudo dnf downgrade fortisandbox-cloud-<VERSION_BEFORE_5.0.4> sudo dnf versionlock add fortisandbox-cloud

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.

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-2026-39812?

fortisandbox: upgrade to 4.4.9, 5.0.6; fortisandbox cloud: upgrade to newer than 24.1.4436. Exact commands for each OS are on this page.

Is CVE-2026-39812 being exploited?

CVE-2026-39812 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-2026-39812 affect?

CVE-2026-39812 affects fortisandbox, fortisandbox cloud. Severity is medium (CVSS 4.8). A improper neutralization of input during web page generation ('cross-site scripting') vulnerability in Fortinet FortiSandbox 5.0.0 through 5.0.5, FortiSandbox 4.4.0 through 4.4.8, FortiSandbox 4.2 all versions, FortiSandbox PaaS 5.0.0 thro

How urgent is CVE-2026-39812?

Priority 19/100. No elevated risk signals yet.

Software pages

Fortinet vulnerabilities

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References

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