---
id: "CVE-2026-121528"
page: "https://infrastack.ai/live/CVE-2026-121528"
kind: "vulnerability"
aliases: ["CVE-2026-121528"]
title: "FortiOS: improper certificate validation lets attackers intercept SSL VPN portal traffic"
severity: "high"
cvss: 8.1
epss: null
exploited: false
status: "open"
category: "vendor"
products: []
ecosystems: []
tags: ["firewall", "fortigate", "fortios", "ssl-vpn", "vendor"]
not_affected_if: ["unknown"]
published_at: "2026-11-11T22:17:11+00:00"
first_seen_at: "2026-11-11T22:29:27+00:00"
updated_at: "2026-11-11T22:31:49+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-121528", "first_seen_at": "2026-11-11T22:29:27+00:00"}]
exploit_sources: []
---

# FortiOS: improper certificate validation lets attackers intercept SSL VPN portal traffic

Link for people: https://infrastack.ai/live/CVE-2026-121528 (this .md is for agents)

FortiOS SSL VPN web portal does not properly validate certificates on its connection to the backend website. A remote, unauthenticated attacker positioned in the network path can perform a man-in-the-middle attack and read or alter traffic between the portal and the backend.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the FortiOS version on the device against the affected ranges: `7.6.0` through `7.6.4`, `7.4.0` through `7.4.9`, `7.2.0` through `7.2.13`.
- Confirm whether SSL VPN web portal is enabled on the device; the sources do not say which configuration is required.

## Fix

- Fixed versions are not stated in the sources provided; check the Fortinet advisory for the fixed release in each branch.

## Timeline

- 2026-11-11T22:29:27+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-121528

## From the sources

A improper certificate validation vulnerability in Fortinet FortiOS 7.6.0 through 7.6.4, FortiOS 7.4.0 through 7.4.9, FortiOS 7.2.0 through 7.2.13 may allow a remote and unauthenticated attacker to perform a Man-in-the-Middle attack on the communication channel between the SSLVPN web portal and the backend destination website.

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