FortiGate - VPN SSL Settings Modified

Status: experimental
Severity: medium
Log source: product fortigate, service event
Author: Marco Pedrinazzi (@pedrinazziM) (InTheCyber)
Source: github.com/SigmaHQ/sigma

Detects the modification of VPN SSL Settings (for example, the modification of authentication rules). This behavior was observed in pair with the addition of a VPN SSL Web Portal.

Known false positives

VPN SSL settings can be changed for legitimate purposes.

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	`T1133` External Remote Services
Persistence	`T1133` External Remote Services

Rule body

title: FortiGate - VPN SSL Settings Modified
id: 8b5dacf2-aeb7-459d-b133-678eb696d410
status: experimental
description: |
    Detects the modification of VPN SSL Settings (for example, the modification of authentication rules).
    This behavior was observed in pair with the addition of a VPN SSL Web Portal.
references:
    - https://www.fortiguard.com/psirt/FG-IR-24-535
    - https://docs.fortinet.com/document/fortigate/7.6.4/fortios-log-message-reference/398/event
    - https://docs.fortinet.com/document/fortigate/7.6.4/cli-reference/114404382/config-vpn-ssl-settings
    - https://docs.fortinet.com/document/fortigate/7.6.4/fortios-log-message-reference/44546/44546-logid-event-config-attr
author: Marco Pedrinazzi (@pedrinazziM) (InTheCyber)
date: 2025-11-01
tags:
    - attack.persistence
    - attack.initial-access
    - attack.t1133
logsource:
    product: fortigate
    service: event
detection:
    selection:
        action: 'Edit'
        cfgpath: 'vpn.ssl.settings'
    condition: selection
falsepositives:
    - VPN SSL settings can be changed for legitimate purposes.
level: medium

Stages and Predicates

Stage 0: `condition`

selection

Stage 1: `selection`

selection:
    action: 'Edit'
    cfgpath: 'vpn.ssl.settings'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`action`	eq	`Edit`	`field:"action" kind:eq value:"Edit"`
`cfgpath`	eq	`vpn.ssl.settings`	`field:"cfgpath" kind:eq value:"vpn.ssl.settings"`