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Introduction:
The digital perimeter has been breached on an industrial scale. The “FortiBleed” campaign, uncovered by Unit 42 and security researcher Volodymyr Diachenko, represents one of the most aggressive credential-harvesting operations to date, targeting Fortinet, Sophos, and MSSQL devices with billions of login attempts. This isn’t a sophisticated zero-day exploit; it is a brutal, numbers-driven assault on weak password hygiene and exposed management interfaces, leveraging a self-reinforcing cycle of credential theft and reuse that leaves organizations vulnerable to complete network takeover.
Learning Objectives:
- Understand the multi-phase attack chain of the FortiBleed campaign, from initial password spraying to offline cracking and lateral movement.
- Learn to audit remote access logs on Linux, Windows, and network devices to detect password spraying indicators.
- Implement robust defensive measures including Multi-Factor Authentication (MFA), Zero Trust Architecture, and secure credential management.
You Should Know:
1. The Anatomy of the FortiBleed Attack Chain
The FortiBleed campaign operates as a highly automated, five-phase industrial-scale operation. It begins with mass reconnaissance, utilizing tools like Masscan for port sweeps and a custom `Shodan_Recon` tool to identify over 430,000 FortiGate devices and 247,000 Sophos portals. The attackers then employ a curated password list—developed from previous breaches and infostealer logs—to conduct password spraying against exposed SSL-VPN and management interfaces. This phase alone generated approximately 1.16 billion login attempts against FortiGate devices and over 2.1 billion attempts against MSSQL servers.
Once initial access is gained, the attackers escalate privileges and extract device configuration files, including stored credentials. The core of the operation is a Golang-based tool called FortigateSniffer, which abuses the legitimate FortiOS diagnostic command `diagnose sniffer packet` to passively capture authentication traffic across 24 protocols, including Kerberos, RADIUS, NTLM, and LDAP, without deploying any malware. Finally, the stolen hashes are cracked offline using a distributed GPU cluster managed via Hashtopolis and Hashcat, adding newly cracked credentials back into the password list for subsequent attacks. This creates a self-reinforcing loop where one compromised credential leads to broader access, including Active Directory environments.
- Hunting for the Needle: Auditing Logs for Password Spraying
Detecting a password spraying attack requires a shift in perspective from traditional brute-force detection. Instead of many failures for a single user, you are looking for a small number of failures across many users.
- On Linux Systems: Focus on authentication logs. Use the `lastb` command to display failed login attempts recorded in
/var/log/btmp. To spot a spray, look for patterns where multiple distinct usernames have a single failed attempt from the same source IP.Display failed login attempts with source IP, sorted and counted sudo lastb -a | awk '{print $3}' | sort | uniq -c | sort -1r Check auth.log for repeated failures from a single IP across many users sudo grep "Failed password" /var/log/auth.log | awk '{print $(NF-3)}' | sort | uniq -c | sort -1rMore advanced analysis can be performed using tools like `LogAnalysisTool` to detect password spraying patterns in
wtmp,btmp, and secure logs. -
On Windows Systems: The primary event to monitor is Event ID 4625 (An account failed to log on). A password spray will manifest as a high volume of 4625 events with different usernames but the same source network address. You can use PowerShell to query the Security event log for this pattern:
Query for failed logons in the last 24 hours, grouped by source IP Get-WinEvent -FilterHashtable @{LogName='Security'; ID=4625; StartTime=(Get-Date).AddDays(-1)} | ForEach-Object { $_.Properties[bash].Value } | Group-Object | Sort-Object Count -DescendingAdditionally, monitor for Event ID 4740 (Account Lockout), as a spray can trigger lockouts if the account lockout threshold is low.
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On Fortinet and Sophos Devices: Audit remote access logs for successful logins shortly after large-volume password failure events. Look for unexpected administrator access from unknown IP addresses and check for the creation of unrecognized accounts, such as “forticloud” or “fortiuser”.
3. The Unbreakable Shield: Enforcing Multi-Factor Authentication (MFA)
Unit 42, the CSA, and Fortinet all unanimously agree: implementing MFA is the single most critical defense against password spraying. MFA breaks the attack chain by rendering stolen passwords useless without the second factor.
- Fortinet FortiGate: Integrate MFA for all administrator and VPN user accounts. This can be achieved via RADIUS with a solution like Cisco Duo, SAML with providers like BeyondIdentity, or FortiToken. Upgrade to FortiOS 7.4, 7.6, or 8.0 to enable PBKDF2 hashing of administrator credentials, replacing the weaker SHA-256 hashes. Use the command `set login-lockout-upon-weaker-encryption` to remove legacy password hashing settings.
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Sophos Firewalls: Enable MFA on all externally accessible accounts. Sophos has confirmed that the threat actors specifically targeted appliances that lacked MFA protection.
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MSSQL Servers: While MFA is less common for SQL authentication, you must enforce strong authentication mechanisms. Consider using Azure Active Directory authentication for cloud-based SQL instances, which supports MFA, or integrate with RADIUS for on-premises deployments. Monitor SQL error logs for failed login attempts (Event ID 18456) as an indicator of spraying.
4. Zero Trust and Attack Surface Reduction
Adopting a Zero Trust Architecture is paramount. Never expose management interfaces directly to the public internet. Leverage “jump boxes” and Zero Trust Network Access (ZTNA) policies to create a secure, mediated path for administrative access.
- Reduce the Attack Surface:
- FortiGate: Restrict external management access via trusted hosts, apply a local-in policy, or, ideally, disable internet-facing administrative access entirely.
- General: Change default credentials for all accounts, ensuring long, complex passwords are used. Disable unused accounts to limit the attack surface.
- Patch Management: Ensure you have the latest software versions and patches installed to mitigate known vulnerabilities, including local privilege escalation vulnerabilities that could be exploited post-compromise.
5. Credential Hygiene and Post-Compromise Actions
The FortiBleed campaign thrives on credential reuse and weak passwords. Organizations must enforce strong password policies and ensure credentials are not reused across systems.
- Immediate Actions for Affected Organizations:
- Terminate Sessions: Terminate all active administrative and VPN sessions.
- Reset Credentials: Reset all Fortinet VPN and administrative passwords, especially on internet-facing systems.
- Validate Configuration: Review firewall, VPN user, and other configuration settings for unauthorized changes. Pay particular attention to unrecognized accounts.
- Consider Factory Reset: If there is evidence of unauthorized modifications or other indicators of compromise, treat the devices as compromised and perform a factory reset to eliminate any potential persistence.
- Proactive Defenses:
- PAN-OS Users: Leverage the Master Key to encrypt cryptographic keys using AES-256-GCM and store only SHA-256 encrypted and salted hashes.
- Credential Monitoring: Utilize services like Unit 42’s Deep and Dark Web monitoring to identify leaked credentials that surface on the dark web, reducing the time between detection and response.
What Undercode Say:
- Key Takeaway 1: FortiBleed is a stark reminder that basic security hygiene is the first line of defense. The attackers are not using novel exploits; they are exploiting weak passwords, exposed interfaces, and a lack of MFA at a massive scale.
- Key Takeaway 2: Detection is a race against automation. By the time you see a successful login, the attackers may have already extracted configurations, cracked hashes, and established persistence. Proactive hunting in logs for the pattern of a spray—many users, few attempts—is essential for early intervention.
Analysis:
The FortiBleed campaign is a masterclass in operational efficiency. It demonstrates how initial access brokers (IABs) are professionalizing, using AI-assisted coding to develop custom tools and automating every stage of the attack chain. The scale is breathtaking, with over 110 million credentials harvested across 659+ pipelines. The attackers’ use of a Telegram bot for live telemetry and rented GPU capacity for cracking shows a level of sophistication that rivals nation-state actors. The confirmed breach of a NATO-aligned defense contractor, with over 105 GB of sensitive data exfiltrated, underscores the real-world impact of these operations. Organizations must move beyond reactive patching and embrace a Zero Trust posture, where every access request is continuously verified, and the principle of least privilege is strictly enforced. The era of trusting a password is over.
Prediction:
- +1 The FortiBleed incident will catalyze a rapid, widespread adoption of MFA and Zero Trust principles across the enterprise, particularly in the SMB sector which has been historically slow to adopt these measures. The sheer scale of the leak will force a cultural shift in how credentials are managed.
- -1 The success of this campaign will likely inspire copycat operations. The playbook—mass scanning, password spraying, credential stuffing, and configuration extraction—is now public. We can expect a surge in similar attacks targeting other edge devices and VPN appliances in the coming months.
- -1 The reliance on legacy hashing algorithms (SHA-256) in many FortiGate devices, even after upgrades, presents a long-tail risk. Organizations that fail to enforce PBKDF2 and reset credentials post-upgrade will remain vulnerable for years, providing a persistent attack vector for threat actors.
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