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Introduction:
In June 2026, the cybersecurity community was rocked by the discovery of “FortiBleed,” a massive credential exposure campaign that has compromised over 86,000 internet-facing Fortinet FortiGate firewalls and VPN gateways across 194 countries. Unlike a zero-day vulnerability, this campaign exploits the all-too-common human factors of credential reuse, weak password hygiene, and the absence of multi-factor authentication (MFA), allowing threat actors to gain unauthorized administrative access and potentially move laterally within enterprise networks. This article provides a comprehensive technical breakdown of the FortiBleed incident, offering step-by-step hardening guides, verification commands, and strategic recommendations to secure your Fortinet infrastructure against this ongoing threat.
Learning Objectives:
- Objective 1: Understand the technical mechanics and scale of the FortiBleed credential-harvesting campaign.
- Objective 2: Learn how to identify if your organization’s FortiGate devices have been compromised.
- Objective 3: Master the immediate response and long-term hardening techniques, including CLI commands and configuration changes, to mitigate the risk of intrusion.
You Should Know:
- Understanding the FortiBleed Attack Vector: Credential Reuse and Brute-Force at Scale
The FortiBleed campaign is not a sophisticated exploit of a new software flaw but a large-scale, automated assault on authentication mechanisms. Fortinet’s analysis indicates that threat actors are primarily reusing credentials from previous data breaches and infostealer malware logs. They are also employing brute-force and dictionary attacks against FortiGate administrative interfaces and SSL VPN portals that lack MFA and have weak password policies.
The scale of this operation is staggering. Security researchers estimate the attackers executed roughly 1.16 billion credential attempts targeting more than 320,000 FortiGate targets. This campaign, orchestrated by a Russian-speaking threat actor, has resulted in a verified database of 86,644 confirmed working credentials. The attackers are not just stopping at gaining access; they are actively moving laterally. Reports indicate they intercept SSL VPN authentication, crack password hashes using a 45-GPU cluster managed via Hashtopolis, and pivot into internal Active Directory environments. This highlights that credential compromise is often the first step in a more devastating chain of attacks.
2. Immediate Response: Terminate Sessions and Reset Credentials
If you suspect your FortiGate device is compromised or as a precautionary measure, the first and most critical step is to terminate all active sessions and reset all credentials. This action immediately invalidates any stolen session tokens or passwords the attacker may possess.
Step-by-Step Guide:
1. Terminate All Active Administrative Sessions:
- Access your FortiGate device via SSH or the web-based GUI.
- To terminate all active administrative sessions via the CLI, use the following command:
execute session kill all
- Alternatively, to terminate a specific session, first list all sessions:
diagnose sys session list
- Then, kill the specific session using its session ID:
diagnose sys session kill <session_id>
- For a more targeted approach to kill all SSL VPN sessions, use:
diagnose vpn ssl kill
2. Reset All Administrative and VPN Passwords:
- Via CLI for Admin Accounts: To reset the password for a specific administrator account (e.g., “admin”), use the following command. You will be prompted to enter and confirm the new password.
config system admin edit admin set password end
- Via CLI for VPN User Accounts: To reset a password for a local VPN user, use:
config user local edit <username> set password end
- Via GUI: Navigate to `System > Administrators` and `VPN > SSL-VPN Settings` (or
User & Device > User > Local) to manually change passwords. - Critical: Ensure all new passwords are complex, unique, and comply with a strong password policy. Enforce a minimum length of 15 characters, including uppercase, lowercase, numbers, and special characters.
3. Fortify Authentication: Enforce MFA and PBKDF2
Multi-factor authentication is the single most effective control against credential-based attacks. CISA and Fortinet both strongly urge the immediate enforcement of phishing-resistant MFA on all administrative and VPN user accounts. Additionally, upgrading credential storage to PBKDF2 is crucial to protect passwords even if they are exfiltrated.
Step-by-Step Guide:
1. Enforce MFA on Administrator Accounts:
- Via GUI: Navigate to
System > Administrators. Edit an admin user. Under “Authentication,” select “Two-factor authentication” and choose the method (e.g., FortiToken, email, or SMS). - Via CLI: To enable MFA for an admin, you can bind a FortiToken to the account:
config system admin edit admin set fortitoken <serial_number> set two-factor enable end
2. Enforce MFA on SSL VPN Users:
- Via GUI: Go to
VPN > SSL-VPN Portals. Edit the portal used by your users. Under the “Authentication” section, enable “Two-factor authentication.” - Via CLI: Configure the SSL VPN authentication rule to require MFA.
config vpn ssl web portal edit <portal_name> set two-factor enable end
3. Enable PBKDF2 for Credential Hashing:
- FortiOS versions 7.4, 7.6, and 8.0 support PBKDF2 for hashing administrator credentials. First, ensure your FortiGate is running a supported version.
- To enforce PBKDF2 and remove legacy, weaker hashes (like MD5), use the following CLI command:
config system global set login-lockout-upon-weaker-encryption enable end
- Critical: Executing this command will lock out any administrator account that is still using a weaker hash algorithm after a failed login attempt. You should first ensure all admins have logged in successfully to have their hashes upgraded to PBKDF2.
- Audit and Cleanse: Validate Configurations and Review Logs
Once an attacker gains a foothold, they often create backdoor accounts or alter configurations to maintain persistence. A thorough audit is essential.
Step-by-Step Guide:
1. Review and Validate Firewall and VPN Configurations:
- Check for Unauthorized Admin Accounts: Review all administrator accounts. Pay close attention to unrecognized or generic account names such as “forticloud,” “fortiuser,” “fortinet-support,” and “fortinet-tech-support”.
show system admin
- Check for Unauthorized Local Users: Review local user accounts that may have been created for VPN access.
show user local
- Compare Against a Known-Good Baseline: If available, compare your current configuration file against a known-good backup to identify any unauthorized changes. This can be done by exporting the config and using a diff tool.
2. Perform a Deep Dive into Logs:
- Check Admin Access Logs: Look for unexpected administrator access from unknown or suspicious IP addresses.
execute log filter view execute log filter device 0 execute log filter field logdesc "Administrator login successful" execute log display
- Check Domain Controller Logs: Review domain controller logs for signs of lateral movement, such as unusual access patterns, suspicious account creations, or atypical authentication requests.
- Check SSL VPN Logs: Look for successful VPN logins from unusual geographic locations or at odd hours.
3. Remove Suspicious or Unneeded Accounts:
- If you identify any unauthorized or suspicious accounts, do not simply disable them without further investigation. The attacker may have other persistence mechanisms. However, immediate removal is critical.
- Delete an Admin Account via CLI:
config system admin delete <suspicious_username> end
5. Reduce Attack Surface: Lock Down Management Access
The most effective way to prevent credential-based attacks is to ensure that your management interfaces are not accessible from the public internet.
Step-by-Step Guide:
1. Restrict Administrative Access via Trusted Hosts:
- This is the most basic form of access control. You can specify which IP addresses are allowed to access the administrative interface.
config system admin edit admin set trusted-hosts <IP_address> <netmask> ... end
2. Implement a Local-in Policy (Recommended):
- A local-in policy provides more granular control and is considered a better security practice than trusted hosts. It allows you to define explicit rules for traffic destined for the FortiGate itself.
- Example: Allow HTTPS access from a specific management subnet only.
config firewall local-in-policy edit 1 set intf "wan1" set srcaddr "management_subnet" set dstaddr "all" set action accept set service "HTTPS" set schedule "always" end edit 2 set intf "wan1" set srcaddr "all" set dstaddr "all" set action deny set service "HTTPS" set schedule "always" end
3. Disable Internet-Facing Administration (Best Practice):
- The most secure option is to completely disable administrative access from the internet. This can be done by not allowing HTTPS/SSH traffic from the WAN interface in your firewall policies.
6. Advanced Response: Consider a Factory Reset
If you discover evidence of compromise (e.g., unauthorized accounts, configuration changes, or suspicious logs), changing passwords and deleting accounts may not be sufficient. Attackers may have installed backdoors or altered the system at a deeper level. In such cases, a factory reset is the only way to ensure a clean slate.
Step-by-Step Guide:
- Backup Critical Configuration (If Safe): If you have a known-good backup from before the suspected compromise, you can use it. Otherwise, it’s risky to back up a potentially compromised config.
2. Perform a Factory Reset via CLI:
- Connect to the FortiGate via the console port and execute the following command:
execute factoryreset
- The device will reboot and return to its default factory settings.
3. Perform a Factory Reset via Hardware Button:
- Locate the reset button on the physical device. Press and hold it for about 10-15 seconds until the device reboots.
- Reconfigure from a Known-Good Backup: After the reset, restore the configuration from a backup that you are confident is clean. Do not restore from a backup that may be compromised.
What Undercode Say:
- Key Takeaway 1: The FortiBleed incident underscores a fundamental truth in cybersecurity: the human element remains the weakest link. The attack’s success is not due to a sophisticated zero-day, but rather the systemic failure to enforce basic security hygiene like MFA and strong, unique passwords. This is a stark reminder that investing in robust authentication controls is as critical as patching software vulnerabilities.
- Key Takeaway 2: The scale and speed of the FortiBleed campaign (with over a billion credential attempts) demonstrate the power of automation in modern cyberattacks. Defenders must adopt a similar mindset, using automation for continuous monitoring, log analysis, and threat hunting. The ability to quickly detect and respond to anomalies is paramount.
Analysis:
The FortiBleed event is a watershed moment for network security, serving as a brutal, real-world stress test of enterprise authentication postures. The fact that over 86,000 devices were compromised through credential reuse alone highlights a massive, persistent gap in security culture. It forces a critical reassessment of how we manage identities and access. The response from CISA and other agencies is not just a set of recommendations; it is a mandate for change. The path forward requires a multi-layered strategy: enforcing MFA as a non-1egotiable standard, adopting phishing-resistant methods like FIDO2, modernizing password storage with algorithms like PBKDF2, and ruthlessly minimizing the attack surface by locking down management interfaces. Organizations that fail to learn from FortiBleed are likely to find themselves as the next headline.
Prediction:
- -1: The immediate fallout from FortiBleed will be severe, with a surge in ransomware and data breach incidents as attackers leverage the compromised credentials to infiltrate networks, install backdoors, and exfiltrate sensitive data over the coming months.
- +1: In the long term, FortiBleed will act as a powerful catalyst, accelerating the global adoption of passwordless authentication and forcing vendors and organizations to prioritize identity-centric security models over traditional perimeter-based defenses.
- -1: The incident will also lead to a wave of class-action lawsuits and regulatory scrutiny, particularly for organizations in critical infrastructure sectors that failed to implement basic security measures like MFA, exposing them to significant financial and reputational damage.
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