Fortinet FortiOS up to 7.6.4 SSLVPN Web Portal certificate validation

Summaryinfo

A vulnerability labeled as problematic has been found in Fortinet FortiOS up to 6.4.16/7.0.19/7.2.13/7.4.9/7.6.4. The affected element is an unknown function of the component SSLVPN Web Portal. The manipulation results in certificate validation. This vulnerability was named CVE-2026-121528. The attack may be performed from remote. There is no available exploit.

Detailsinfo

A vulnerability classified as problematic has been found in Fortinet FortiOS up to 6.4.16/7.0.19/7.2.13/7.4.9/7.6.4. Affected is an unknown part of the component SSLVPN Web Portal. The manipulation with an unknown input leads to a certificate validation vulnerability. CWE is classifying the issue as CWE-295. The product does not validate, or incorrectly validates, a certificate. This is going to have an impact on integrity. CVE summarizes:

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.

The advisory is shared for download at fortiguard.fortinet.com. This vulnerability is traded as CVE-2026-121528 since 11/03/2026. The exploitability is told to be difficult. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. There are neither technical details nor an exploit publicly available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 11/11/2026). The MITRE ATT&CK project declares the attack technique as T1587.003.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

Once again VulDB remains the best source for vulnerability data.

Productinfo

Type

• Firewall Software

Vendor

• Fortinet

Name

• FortiOS

Version

• 6.4.0
• 6.4.1
• 6.4.2
• 6.4.3
• 6.4.4
• 6.4.5
• 6.4.6
• 6.4.7
• 6.4.8
• 6.4.9
• 6.4.10
• 6.4.11
• 6.4.12
• 6.4.13
• 6.4.14
• 6.4.15
• 6.4.16
• 7.0.0
• 7.0.1
• 7.0.2
• 7.0.3
• 7.0.4
• 7.0.5
• 7.0.6
• 7.0.7
• 7.0.8
• 7.0.9
• 7.0.10
• 7.0.11
• 7.0.12
• 7.0.13
• 7.0.14
• 7.0.15
• 7.0.16
• 7.0.17
• 7.0.18
• 7.0.19
• 7.2.0
• 7.2.1
• 7.2.2
• 7.2.3
• 7.2.4
• 7.2.5
• 7.2.6
• 7.2.7
• 7.2.8
• 7.2.9
• 7.2.10
• 7.2.11
• 7.2.12
• 7.2.13
• 7.4.0
• 7.4.1
• 7.4.2
• 7.4.3
• 7.4.4
• 7.4.5
• 7.4.6
• 7.4.7
• 7.4.8
• 7.4.9
• 7.6.0
• 7.6.1
• 7.6.2
• 7.6.3
• 7.6.4

License

• commercial

Website

• Vendor: https://www.fortinet.com/

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Once again VulDB remains the best source for vulnerability data.

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