Web application firewall rules bypass in FortiWeb

Published: 2025-03-13

Risk	Medium
Patch available	YES
Number of vulnerabilities	2
CVE-ID	CVE-2023-42784 CVE-2024-55594
CWE-ID	CWE-20
Exploitation vector	Network
Public exploit	N/A
Vulnerable software	Fortinet FortiWeb Server applications / Remote management servers, RDP, SSH
Vendor	Fortinet, Inc

Security Bulletin

This security bulletin contains information about 2 vulnerabilities.

1) Input validation error

EUVDB-ID: #VU105694

Risk: Medium

CVSSv4.0: 1.7 [CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N/E:U/U:Green]

CVE-ID: CVE-2023-42784

CWE-ID: CWE-20 - Improper input validation

Exploit availability: No

Description

The vulnerability allows a remote attacker to bypass firewall protection.

The vulnerability exists due to insufficient validation of files. A remote attacker can send a specially crafted HTTP request with an empty filename and bypass implemented firewall rules.

Mitigation

Install updates from vendor's website.

MANDATORY steps to enable the fix :

Update to the latest FDS version
Approve signature 050240001
Enable signature policy in corresponding Web Protection Profile, "Say Standard Protection"
Go to Web Protection/Input Validation/File Security/File Security Rule
Click Create New, set name to "file_security"
In "Request URL Type" choose "Regular Expression" in "Request URL"
Add "/" Click "OK"
Go to Web Protection/Input Validation/File Security/File Security Policy
Click Create New
Set a name say file_test
Enable "Signature Detection", Click "OK"
Click "Create New", Select the above added "File Security Rule", Click "OK"
In CLI :

'''
Config waf http-protocol-parameter-restriction

edit "hpc1"

set chunk-size-action alert_deny

set chunk-size-severity High

end

'''

Vulnerable software versions

Fortinet FortiWeb: 7.0.0 - 7.4.6

CPE2.3

External links

http://fortiguard.fortinet.com/psirt/FG-IR-23-115

Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

How the attacker can exploit this vulnerability?

The attacker would have to send a specially crafted request to the affected application in order to exploit this vulnerability.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.

2) Input validation error

EUVDB-ID: #VU105695