FortiGate Web Exploitation Indicators for CVE-2023-27997 via Remote Host/Login Checks

Flags GET/POST requests to FortiGate /remote validation/login endpoints containing "enc=" as potential CVE-2023-27997 exploitation indicators.

FreeReviewedSigma · Medium · v5

Category: webserver
Author: Sergio Palacios Dominguez, Nasreddine Bencherchali (Nextron Systems) (SigmaHQ), DRL 1.1
Published: 2023-07-28
Updated: 2026-07-31

Analysis Detection

ATT&CK techniques

Initial Access

Recon
Resource Dev
Initial Access
- T1190Exploit Public-Facing Application
Execution
Persistence
Priv Esc
Defense Evasion
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

This rule flags potential exploitation attempts against FortiGate web endpoints by matching GET/POST requests whose URI query contains '/remote/hostcheck_validate' or '/remote/logincheck' along with an 'enc=' parameter. Attackers often probe vulnerable components using these request patterns and may include an encoding parameter to carry exploit-related data. Telemetry required includes webserver logs with HTTP method, full request URI/query, and query string contents to observe both the targeted paths and the presence of 'enc='.

Reporting behind it

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FortiGate Web Exploitation Indicators for CVE-2023-27997 via Remote Host/Login Checks

Pivot detection · T1190 · 9 related

Changelog

v5
Candidate ingested via manual entry.2026-07-31
v4
Candidate ingested via manual entry.2026-07-31
v3
Candidate ingested via manual entry.2026-07-31
v2
Candidate ingested via manual entry.2026-07-31
v1
No changelog recorded for this version.2026-07-30

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.

fortigate-web-logs-indicators-of-cve-2023-27997-exploitation-attempt-31e4e649

title: FortiGate Web Exploitation Indicators for CVE-2023-27997 via Remote Host/Login Checks
id: 2846b98e-7366-4484-80c8-f87524bd8318
status: test
description: This rule flags potential exploitation attempts against FortiGate web endpoints by matching GET/POST requests whose URI query contains '/remote/hostcheck_validate' or '/remote/logincheck' along with an 'enc=' parameter. Attackers often probe vulnerable components using these request patterns and may include an encoding parameter to carry exploit-related data. Telemetry required includes webserver logs with HTTP method, full request URI/query, and query string contents to observe both the targeted paths and the presence of 'enc='.
references:
  - https://blog.lexfo.fr/Forensics-xortigate-notice.html
  - https://blog.lexfo.fr/xortigate-cve-2023-27997.html
  - https://research.kudelskisecurity.com/2023/06/12/cve-2023-27997-fortigate-ssl-vpn/
  - https://labs.watchtowr.com/xortigate-or-cve-2023-27997/
  - https://github.com/SigmaHQ/sigma/blob/master/rules-emerging-threats/2023/Exploits/CVE-2023-27997/web_cve_2023_27997_pre_authentication_rce.yml
author: Sergio Palacios Dominguez, Nasreddine Bencherchali (Nextron Systems), Huntrule Team
date: 2023-07-28
tags:
  - attack.initial-access
  - attack.t1190
  - cve.2023-27997
  - detection.emerging-threats
logsource:
  category: webserver
detection:
  selection_uri:
    cs-method:
      - GET
      - POST
    cs-uri-query|contains:
      - /remote/hostcheck_validate
      - /remote/logincheck
  selection_keywords:
    - enc=
  condition: all of selection_*
falsepositives:
  - Unknown
level: medium
license: DRL-1.1
related:
  - id: 31e4e649-7394-4fd2-9ae7-dbc61eebb550
    type: derived

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