CVE-2026-59840: A buffer over-read vulnerability in Fortinet FortiOS 7.6.0 through 7.6.3, FortiOS 7.4.0 through 7.4.8, FortiOS

Q: How do I fix CVE-2026-59840?

fortiproxy: upgrade to 7.4.14, 7.6.6; fortios: upgrade to 7.4.9. Exact commands for each OS are on this page.

Q: Is CVE-2026-59840 being exploited?

CVE-2026-59840 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-59840 affect?

CVE-2026-59840 affects fortiproxy, fortios. Severity is medium (CVSS 4.3). A buffer over-read vulnerability in Fortinet FortiOS 7.6.0 through 7.6.3, FortiOS 7.4.0 through 7.4.8, FortiOS 7.2 all versions, FortiOS 7.0 all versions, FortiOS 6.4 all versions, FortiProxy 7.6.0 through 7.6.5, FortiProxy 7.4.0 through 7.

Q: How urgent is CVE-2026-59840?

Priority 21/100. No elevated risk signals yet.

Routine

MEDIUM 4.3UPGRADEUPGRADE

CVE-2026-59840 is a medium-severity flaw (CVSS 4.3) affecting fortiproxy, fortios. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A buffer over-read vulnerability in Fortinet FortiOS 7.6.0 through 7.6.3, FortiOS 7.4.0 through 7.4.8, FortiOS 7.2 all versions, FortiOS 7.0 all versions, FortiOS 6.4 all versions, FortiProxy 7.6.0 through 7.6.5, FortiProxy 7.4.0 through 7.4.13, FortiProxy 7.2 all versions, FortiProxy 7.0 all versions may allow attacker to information disclosure via <insert attack vector here>

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	4.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.3% (top 77%)
CISA exploited list	No
Weakness	CWE-126
Published	2026-07-14
Last modified	2026-10-24

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

Last updated 2026-10-24 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-14 16:17 UTCPublished CVE record published
2026-10-24 21:10 UTCUpdated Record last modified

fortinet fortiproxy UPGRADE

Affected: >= 7.2.0 and < 7.4.14 · >= 7.6.0 and < 7.6.6

Fixed in: 7.4.14, 7.6.6

Safe to downgrade to: a release before 7.2.0

1. Check installed version

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

2. UPGRADE to 7.4.14 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade fortiproxy

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 7.2.0 (Debian / Ubuntu)

apt-cache madison fortiproxy sudo apt install fortiproxy=<VERSION_BEFORE_7.2.0> sudo apt-mark hold fortiproxy

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

dnf --showduplicates list fortiproxy sudo dnf downgrade fortiproxy-<VERSION_BEFORE_7.2.0> sudo dnf versionlock add fortiproxy

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 fortios UPGRADE

Affected: >= 7.2.0 and < 7.4.9 · >= 7.6.0 and <= 7.6.2

Fixed in: 7.4.9

Safe to downgrade to: a release before 7.2.0

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

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-2026-59840?

fortiproxy: upgrade to 7.4.14, 7.6.6; fortios: upgrade to 7.4.9. Exact commands for each OS are on this page.

Is CVE-2026-59840 being exploited?

CVE-2026-59840 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-2026-59840 affect?

CVE-2026-59840 affects fortiproxy, fortios. Severity is medium (CVSS 4.3). A buffer over-read vulnerability in Fortinet FortiOS 7.6.0 through 7.6.3, FortiOS 7.4.0 through 7.4.8, FortiOS 7.2 all versions, FortiOS 7.0 all versions, FortiOS 6.4 all versions, FortiProxy 7.6.0 through 7.6.5, FortiProxy 7.4.0 through 7.

How urgent is CVE-2026-59840?

Priority 21/100. No elevated risk signals yet.

Software pages

Fortinet FortiOS vulnerabilities · Fortinet vulnerabilities

Related CVEs

CVE-2026-59837 MEDIUM 6.6 UPGRADE UPGRADE A stack-based buffer overflow vulnerability in Fortinet FortiOS 7.4.0 through 7.4.1, FortiOS 7.2 all versions,
CVE-2026-23573 MEDIUM 6.1 UPGRADE UPGRADE An Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability [CWE-79]
CVE-2026-59839 MEDIUM 5.5 UPGRADE UPGRADE A improper limitation of a pathname to a restricted directory ('path traversal') vulnerability in Fortinet For
CVE-2024-21762 CRITICAL 9.8 EXPLOITED UPGRADE UPGRADE Fortinet FortiOS Out-of-Bound Write Vulnerability
CVE-2025-61624 MEDIUM 6.0 EXPLOITED UPGRADE UPGRADE Fortinet Multiple Products Path Traversal Vulnerability

References

← Back to latest CVEs