CVE-2025-48840 in FortiWeb
Summary
by MITRE • 03/10/2026
An authentication bypass by spoofing vulnerability in Fortinet FortiWeb 7.6.0 through 7.6.3, FortiWeb 7.4.0 through 7.4.8, FortiWeb 7.2 all versions, FortiWeb 7.0 all versions may allow a remote unauthenticated attacker to bypass hostname restrictions via a specially crafted request.
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Analysis
by VulDB Data Team • 03/13/2026
This vulnerability represents a critical authentication bypass flaw that affects multiple versions of Fortinet FortiWeb web application firewalls. The issue stems from insufficient validation of hostname parameters within the authentication flow, allowing malicious actors to spoof legitimate hostnames and bypass critical access controls. The vulnerability specifically impacts FortiWeb versions 7.6.0 through 7.6.3, 7.4.0 through 7.4.8, and all versions of 7.2 and 7.0 releases, creating a widespread exposure across the Fortinet FortiWeb product line. The flaw enables remote unauthenticated attackers to craft specially formatted requests that can circumvent hostname-based restrictions that are typically enforced during the authentication process.
The technical implementation of this vulnerability involves manipulation of HTTP headers or request parameters that contain hostname information. When FortiWeb processes incoming requests, it fails to properly validate or sanitize the hostname values, allowing attackers to inject or modify these parameters to match allowed hostnames. This spoofing mechanism exploits the trust relationship between the firewall and the hostname validation logic, effectively allowing unauthorized access to protected resources. The vulnerability operates at the application layer and can be exploited through standard network protocols without requiring any prior authentication credentials, making it particularly dangerous for organizations relying on FortiWeb for web application protection.
The operational impact of this vulnerability is severe as it fundamentally undermines the security model of FortiWeb deployments. Attackers can potentially access restricted administrative interfaces, bypass content filtering rules, and gain unauthorized access to sensitive web applications protected by the firewall. This vulnerability directly affects the principle of least privilege by allowing unauthorized access to systems that should only be accessible to authenticated administrators. Organizations may experience data breaches, unauthorized modifications to web applications, and complete compromise of web application security controls that FortiWeb was designed to protect against. The attack surface extends to any web application protected by the vulnerable FortiWeb instances, potentially affecting customer data, internal systems, and business-critical applications.
Organizations should immediately implement mitigations including updating to the latest Fortinet FortiWeb versions that contain patches for this vulnerability, implementing additional network-level controls such as firewalls and intrusion detection systems, and conducting comprehensive security assessments of their web application environments. Network administrators should also consider implementing additional hostname validation checks at multiple layers of the network infrastructure, and organizations should review their current access control policies to ensure proper segregation of duties and least privilege principles. The vulnerability aligns with CWE-285 (Improper Authorization) and can be mapped to ATT&CK technique T1078.004 (Valid Accounts: Cloud Accounts) when exploited in cloud environments. Additionally, this vulnerability demonstrates weaknesses in the principle of input validation and highlights the importance of proper hostname verification mechanisms in security-critical applications, making it a prime example of how insufficient parameter validation can lead to complete bypass of authentication controls.