Table of Contents
Key Takeaway
- ⚡ The Flaw: The Fortinet authentication flaw CVE-2026-26035 lets a remote, unauthenticated attacker log in to the FortiWeb GUI or CLI with a random username and password — no credentials required.
- 🎯 The Trigger: The vulnerability is triggered when the wildcard setting for administrator accounts is enabled — a non-default configuration that matches any username on a remote server with the Remote User account.
- 📊 The Scope: Fortinet patched 8 vulnerabilities across its products, including CVE-2026-70468 in FortiManager (authentication bypass allowing impersonation of any FortiGate device) and CVE-2026-70465 in FortiClient for Windows (buffer overflow allowing arbitrary code execution via crafted DNS responses).
- 🏢 The Workaround: For FortiWeb, Fortinet recommends disabling the wildcard setting as an immediate workaround if patching cannot be done immediately. FortiWeb versions 8.0.3, 7.6.7, 7.4.12, and 7.2.13 contain the fix.
- 🔑 What You Should Do: Patch all FortiWeb and FortiManager appliances immediately, disable wildcard admin settings, and audit all FortiGate management certificates for potential impersonation.
The Fortinet authentication flaw disclosed on August 13, 2026, reads like a parody of bad security design: a remote, unauthenticated attacker can log in to a FortiWeb appliance’s management interface with a random username and password. Not a stolen credential. Not a brute-forced password. A random one. The vulnerability, tracked as CVE-2026-26035, exploits a configuration option that was designed for convenience — the wildcard administrator setting — and turns it into an open door that bypasses authentication entirely.
This is not a subtle exploitation path. It is the kind of vulnerability that makes security engineers question how it was ever possible. The answer lies in the interaction between a non-default configuration setting and the authentication mechanism: when the wildcard setting is enabled, the system matches any username on a remote server with the Remote User account, effectively treating any incoming credential as valid. The Fortinet authentication flaw is a reminder that convenience features in security products are attack surfaces, and non-default configurations can introduce vulnerabilities that default deployments do not have.
How the FortiWeb Authentication Bypass Works
According to SecurityWeek’s reporting on Fortinet’s advisory, the Fortinet authentication flaw in FortiWeb is an improper authentication issue impacting deployments configured with specific, non-default settings. The vulnerability is associated with the wildcard setting for administrator accounts, which is disabled by default. When enabled, the system matches any username on a remote server with the Remote User account.
The technical mechanism is straightforward. FortiWeb supports remote authentication through external servers — typically LDAP or RADIUS. The wildcard setting is designed to simplify admin access by matching any username from the remote server to the local Remote User account. When this setting is enabled alongside a defined admin user group, the system matches users on the remote server whose group name matches the defined value. The vulnerability occurs because this matching process does not properly validate the credentials — it accepts any username and password combination as long as the wildcard setting is active and the group name condition is met.
The result is that an attacker who knows the FortiWeb management interface is accessible and the wildcard setting is enabled can log in with literally any username and password. No credential theft. No brute force. No exploit code sophistication. Just a login attempt with random strings. The Fortinet authentication flaw turns the authentication mechanism into a formality.
The FortiManager Impersonation Vulnerability
The Fortinet authentication flaw extends beyond FortiWeb. CVE-2026-70468 is an authentication bypass vulnerability in FortiManager that allows remote attackers to impersonate any FortiGate device managed by FortiManager. This is a different class of vulnerability with potentially broader impact, because FortiManager is the centralized platform that many enterprises use to configure and manage their entire fleet of FortiGate firewalls.
The FortiManager vulnerability requires two conditions: a specific CLI option must be set, and the attacker must possess a valid certificate. While these requirements make exploitation more difficult than the FortiWeb flaw, the impact is significantly more severe. If an attacker can impersonate a FortiGate device, they can potentially push malicious configurations through FortiManager to every firewall in the fleet. This is not a single-device compromise — it is a supply chain attack on the network security infrastructure itself.
The critical infrastructure implication is clear. FortiGate firewalls are deployed at the network perimeter of thousands of organizations worldwide. A compromise that allows an attacker to push configurations to every FortiGate through FortiManager would give the attacker control over the security posture of the entire network — effectively turning the firewall management system into an attack distribution platform.
The FortiClient Buffer Overflow
Fortinet also patched CVE-2026-70465, a high-severity buffer overflow vulnerability in FortiClient for Windows. This vulnerability allows unauthenticated attackers who can modify or craft DNS responses to execute arbitrary code on the affected system. The attack vector is DNS — the attacker does not need to interact with the FortiClient directly. They need only to control DNS responses that the FortiClient processes.
DNS-based attacks are particularly dangerous because they bypass many network security controls. If an attacker can poison a DNS cache, compromise a DNS server, or intercept DNS traffic through a perimeter device compromise, they can deliver the crafted DNS response to FortiClient without directly targeting the endpoint. This makes the vulnerability exploitable from the network level, not just the endpoint level.
The Wildcard Configuration Trap
The Fortinet authentication flaw highlights a broader issue in security product configuration: features designed for administrative convenience can introduce critical vulnerabilities. The wildcard setting in FortiWeb was designed to simplify remote authentication by matching any username from the remote server to the Remote User account. In theory, this is useful for organizations that want to grant administrative access based on group membership rather than individual user accounts. In practice, it creates an authentication bypass that requires no credentials at all.
This pattern is not unique to Fortinet. The Cisco FMC vulnerability involved hardcoded credentials — another convenience feature that became a critical flaw. The Adobe ColdFusion vulnerability included incorrect authorization flaws that could lead to arbitrary code execution. Security products are not immune to the same categories of vulnerabilities that affect the systems they protect. In some cases, they are more vulnerable because the complexity of their feature sets introduces more configuration-dependent attack surfaces.
For organizations, the lesson is that every non-default configuration in a security product should be treated as a potential vulnerability until proven otherwise. The wildcard setting in FortiWeb is disabled by default for a reason. Organizations that enable it should understand the risk they are accepting: an authentication bypass that lets any attacker with network access to the management interface log in with random credentials.
What Organizations Running Fortinet Must Do Now
Fortinet’s patches are available for all affected products. The specific actions depend on which Fortinet products are deployed:
1. FortiWeb — Patch or disable wildcard. Update to FortiWeb 8.0.3, 7.6.7, 7.4.12, or 7.2.13. If patching cannot be done immediately, disable the wildcard setting for administrator accounts. This is the workaround Fortinet recommends, and it eliminates the vulnerability by removing the configuration that enables the authentication bypass.
2. FortiManager — Patch and audit certificates. Update FortiManager to the latest version. Audit all FortiGate device certificates registered with FortiManager for validity. The FortiManager vulnerability requires a valid certificate for exploitation, so ensuring that all registered certificates are legitimate and accounted for reduces the attack surface.
3. FortiClient for Windows — Patch all endpoints. Update FortiClient to the latest version to address the buffer overflow vulnerability. Review DNS infrastructure for potential compromise, as the attack vector relies on crafted DNS responses. The AI patch deployment approach becomes relevant here — when a vendor patches 8 vulnerabilities across multiple products in a single release, organizations need automated patching processes to keep up.
The Perimeter Device Pattern in 2026
The Fortinet authentication flaw is the latest in a year-long pattern of perimeter security device vulnerabilities. The SonicWall zero-day, the VMware vCenter exploit, the GeoServer zero-day, and now the Fortinet authentication flaw all share the same characteristic: they target the infrastructure that organizations rely on for security, not the endpoints they are trying to protect. The CrowdStrike 2026 Global Threat Report documented a 65% increase in average breakout speed, with edge devices as a primary breach point. When the security device is the entry point, the defender’s advantage disappears.
The August Patch Tuesday data showed that the one actively exploited Microsoft bug was rated Important, not Critical. The Fortinet authentication flaw demonstrates the inverse: a vulnerability that sounds Critical (authentication bypass with random credentials) exists in a product that many organizations treat as set-and-forget infrastructure. The severity of a vulnerability is not just its CVSS score — it is also the criticality of the system it affects and the simplicity of the exploitation path. An authentication bypass that requires no credentials on a perimeter security device is as severe as it gets.
The Configuration Audit Imperative
The Fortinet authentication flaw exposes a gap in how most organizations approach security product management: they patch the software but do not audit the configurations. The FortiWeb vulnerability is triggered by a specific setting — the wildcard administrator account — that is disabled by default. Organizations that enabled it did so for a reason, likely administrative convenience, without understanding that they were opening an authentication bypass. This is not a failure of patching. It is a failure of configuration management.
The same principle applies to the FortiManager vulnerability. CVE-2026-70468 requires a specific CLI option to be set. Organizations that have not set this option are not vulnerable, regardless of whether they have patched. But organizations that have set it — perhaps for a specific integration or management workflow — are exposed until the patch is applied. The Adobe ColdFusion vulnerability followed the same pattern: the most severe flaws were in products running specific configurations, not default deployments.
For security teams, this means that patching is necessary but not sufficient. Every non-default configuration in a security product should be documented, justified, and periodically reviewed. The question is not just “are we patched?” but “are we configured safely?” A patched FortiWeb with the wildcard setting enabled is still vulnerable. A patched FortiManager with the wrong CLI option set is still at risk. The extortion-first threat groups are not looking for the hardest targets — they are looking for the easiest ones. And the easiest targets are often the ones where someone enabled a convenience feature without understanding the risk.
Frequently Asked Questions About the Fortinet Authentication Flaw
What is the Fortinet authentication flaw?
The Fortinet authentication flaw refers to CVE-2026-26035, a vulnerability in FortiWeb that allows a remote, unauthenticated attacker to log in to the FortiWeb GUI or CLI with a random username and password. The vulnerability is triggered when the wildcard setting for administrator accounts is enabled.
How does the FortiWeb authentication bypass work?
When the wildcard setting is enabled, FortiWeb matches any username from a remote server with the Remote User account. The vulnerability occurs because this matching process does not properly validate credentials — it accepts any username and password combination as long as the wildcard setting is active and the group name condition is met.
Is the wildcard setting enabled by default in FortiWeb?
No. The wildcard setting for administrator accounts is disabled by default in FortiWeb. The vulnerability only affects deployments where an administrator has explicitly enabled this setting. Fortinet recommends disabling the wildcard setting as a workaround if patching cannot be done immediately.
What is CVE-2026-70468 in FortiManager?
CVE-2026-70468 is an authentication bypass vulnerability in FortiManager that allows remote attackers to impersonate any FortiGate device managed by FortiManager. It requires a specific CLI option to be set and the attacker to possess a valid certificate. If exploited, it could allow pushing malicious configurations to every FortiGate in the fleet.
What is CVE-2026-70465 in FortiClient?
CVE-2026-70465 is a high-severity buffer overflow vulnerability in FortiClient for Windows that allows unauthenticated attackers who can modify or craft DNS responses to execute arbitrary code on the affected system. The attack vector is DNS-based, meaning the attacker does not need direct access to the endpoint.
Which FortiWeb versions contain the fix?
The Fortinet authentication flaw is patched in FortiWeb versions 8.0.3, 7.6.7, 7.4.12, and 7.2.13. Organizations running any of these versions should update immediately. Organizations that cannot patch immediately should disable the wildcard setting as a workaround.
Are these Fortinet vulnerabilities being exploited in the wild?
As of the August 13, 2026, advisory, Fortinet has not confirmed exploitation of any of these vulnerabilities in the wild. However, given the simplicity of the FortiWeb authentication bypass and the history of perimeter device exploitation in 2026, organizations should assume that exploitation will follow disclosure.
Cybersecurity Disclaimer: This article discusses the Fortinet authentication flaw based on publicly reported information from SecurityWeek and Fortinet’s PSIRT advisories. It does not constitute professional cybersecurity advice. Organizations should consult Fortinet’s official security advisories and their security teams for specific patch deployment guidance.
