CISA Flags Fortinet CVE-2025-59718: Improper Signature Verification Under Active Exploitation
Executive Summary
In December 2025, CISA added CVE-2025-59718 to its Known Exploited Vulnerabilities catalog, citing confirmed active exploitation targeting Fortinet's multiple products. This vulnerability involves improper verification of cryptographic signatures, allowing attackers to bypass security controls, execute unauthorized code, or escalate privileges on affected devices. Federal agencies, per BOD 22-01, must remediate this critical issue by the mandated deadline to protect their networks. The flaw’s exploitation risks device compromise and potential lateral movement by sophisticated threat actors, with broad implications for data integrity and operational continuity across affected organizations.
This alert reflects the escalating trend of attackers rapidly weaponizing supply chain or cryptographic flaws in core network infrastructure. As organizations increasingly rely on complex integrations and encrypted communications, such vulnerabilities underscore persistent challenges in managing risk and ensuring trust in critical systems.
Why This Matters Now
Active exploitation of CVE-2025-59718 poses immediate and serious risk to networks relying on Fortinet products. Rapid attacker adoption of this vulnerability highlights the urgent need for patching and reinforces that cryptographic flaws in foundational security tools can lead to widescale breaches and regulatory consequences.
Attack Path Analysis
Attackers exploited CVE-2025-59718 in vulnerable Fortinet products to gain initial access to the environment. Leveraging the improper cryptographic signature verification, they escalated privileges to gain broader control. They then moved laterally between internal workloads using internal cloud APIs or management traffic. The attackers established command and control, likely over encrypted channels, to maintain persistent access. Sensitive data was then exfiltrated via allowed egress pathways, and finally, disruptive actions such as deployment of ransomware or deletion of backups were taken to maximize impact.
Kill Chain Progression
Initial Compromise
Description
Exploitation of CVE-2025-59718 in Fortinet products enabled unauthorized access by bypassing cryptographic signature checks.
Related CVEs
CVE-2025-59718
CVSS 9.8An improper verification of cryptographic signature vulnerability in Fortinet products allows unauthenticated attackers to bypass FortiCloud SSO login authentication via crafted SAML response messages.
Affected Products:
Fortinet FortiOS – 7.6.0 through 7.6.3, 7.4.0 through 7.4.8, 7.2.0 through 7.2.11, 7.0.0 through 7.0.17
Fortinet FortiProxy – 7.6.0 through 7.6.3, 7.4.0 through 7.4.10, 7.2.0 through 7.2.14, 7.0.0 through 7.0.21
Fortinet FortiSwitchManager – 7.2.0 through 7.2.6, 7.0.0 through 7.0.5
Exploit Status:
exploited in the wild
MITRE ATT&CK® Techniques
Exploit Public-Facing Application
Unsecured Credentials
Stage Capabilities: Upload Malware
Access Token Manipulation
Modify Authentication Process
Impair Defenses
Exploitation for Privilege Escalation
Potential Compliance Exposure
Mapping incident impact across multiple compliance frameworks.
PCI DSS 4.0 – Install Security Patches
Control ID: 6.2.4
NYDFS 23 NYCRR 500 – Cybersecurity Policy and Technical Controls
Control ID: 500.03, 500.05
DORA (Regulation (EU) 2022/2554) – ICT Risk Management
Control ID: Article 9
CISA Zero Trust Maturity Model (ZTMM) 2.0 – Continuous Vulnerability Management
Control ID: Asset Management & Vulnerability Management
NIS2 Directive – Cybersecurity Risk Management Measures
Control ID: Article 21
Sector Implications
Industry-specific impact of the vulnerabilities, including operational, regulatory, and cloud security risks.
Government Administration
Federal agencies face mandatory remediation requirements under BOD 22-01 for Fortinet cryptographic signature vulnerabilities, requiring immediate zero trust network segmentation implementation.
Financial Services
Banking systems using Fortinet products vulnerable to cryptographic signature exploitation, threatening encrypted traffic integrity and requiring enhanced east-west traffic security controls.
Health Care / Life Sciences
Healthcare networks face HIPAA compliance violations from Fortinet vulnerability exploitation, necessitating immediate threat detection systems and secure hybrid connectivity deployment.
Telecommunications
Telecom infrastructure exploiting Fortinet products at risk for lateral movement attacks, requiring multicloud visibility controls and inline intrusion prevention system upgrades.
Sources
- CISA Adds One Known Exploited Vulnerability to Cataloghttps://www.cisa.gov/news-events/alerts/2025/12/16/cisa-adds-one-known-exploited-vulnerability-catalogVerified
- Fortinet Security Advisory FG-IR-25-647https://fortiguard.fortinet.com/psirt/FG-IR-25-647Verified
- NVD - CVE-2025-59718https://nvd.nist.gov/vuln/detail/CVE-2025-59718Verified
Frequently Asked Questions
Cloud Native Security Fabric Mitigations and ControlsCNSF
Zero Trust segmentation, workload isolation, egress enforcement, and real-time threat detection available through CNSF controls would have constrained movement, reduced exploitable surface, and minimized the potential for data exfiltration and disruptive impact throughout the kill chain.
Control: Inline IPS (Suricata)
Mitigation: Known exploit signatures could have triggered real-time prevention or detection and blocked initial access attempts.
Control: Zero Trust Segmentation
Mitigation: Unauthorized privilege escalations would be contained to a constrained blast radius.
Control: East-West Traffic Security
Mitigation: Attempts to move laterally across the cloud network would be blocked or closely monitored.
Control: Cloud Firewall (ACF)
Mitigation: Unapproved command and control channels would be identified and egress attempts denied.
Control: Egress Security & Policy Enforcement
Mitigation: Egress filters would prevent or alert on suspicious outbound flows indicative of data exfiltration.
Abnormal behavior indicative of destructive actions would trigger rapid alerting and response.
Impact at a Glance
Affected Business Functions
- Network Security Management
- Access Control Systems
Estimated downtime: 3 days
Estimated loss: $500,000
Potential exposure of network configurations, firewall settings, and administrative credentials, leading to unauthorized access and control over network security devices.
Recommended Actions
Key Takeaways & Next Steps
- • Prioritize remediation of all KEV-listed and actively exploited vulnerabilities across perimeter and internal systems.
- • Deploy inline IPS controls and enforce Zero Trust segmentation to prevent exploitation and limit lateral movement.
- • Implement robust east-west and egress policy enforcement to detect and block unauthorized data transfers and C2 activity.
- • Ensure continuous visibility with anomaly-based threat detection and always-on network monitoring.
- • Regularly validate microsegmentation and hybrid cloud policies to minimize blast radius and ensure resilience against future vulnerabilities.
