Attack Chain

Given the general nature of the vulnerabilities, a likely attack chain could involve the following steps:

1. Reconnaissance: Attacker identifies a vulnerable FortiSandbox instance exposed to the network.
2. XSS Exploitation: Attacker crafts a malicious request containing XSS payload targeting a FortiSandbox web interface.
3. Information Disclosure: Attacker leverages an information disclosure vulnerability to leak sensitive configuration data or credentials.
4. Security Bypass: Attacker circumvents security controls or authentication mechanisms due to a flaw in the FortiSandbox.
5. Code Execution: Attacker exploits a code execution vulnerability to inject and execute arbitrary commands on the system.
6. Privilege Escalation: If necessary, the attacker escalates privileges to gain root or administrator access.
7. Lateral Movement: The attacker uses the compromised FortiSandbox as a pivot point to move laterally within the network.
8. Impact: Depending on the attacker’s objectives, the final impact may include data exfiltration, system disruption, or further compromise of internal systems.

Impact

Successful exploitation of these vulnerabilities could lead to complete compromise of the FortiSandbox appliance, potentially impacting network security monitoring and incident response capabilities. An attacker could gain unauthorized access to sensitive data, disrupt security services, or use the compromised FortiSandbox as a launchpad for further attacks within the network. The impact is significant due to the FortiSandbox’s role in analyzing and mitigating threats.

Recommendation

• Investigate Fortinet’s official security advisories for FortiSandbox to identify specific CVEs and affected versions related to these vulnerabilities.
• Apply any available patches or workarounds provided by Fortinet to mitigate the identified vulnerabilities.
• Monitor web server logs on the FortiSandbox for suspicious activity, such as unusual HTTP requests or attempts to access sensitive files (reference: webserver log source in Sigma rules).
• Implement network segmentation to limit the potential impact of a compromised FortiSandbox instance (reference: network_connection log source).
• Deploy the Sigma rules in this brief to your SIEM and tune for your environment to detect exploitation attempts.

Attack Chain

1. The attacker identifies a vulnerable FortiSandbox instance running a version between 4.4.0 and 4.4.8.
2. The attacker crafts a malicious HTTP request containing OS command injection payloads within a vulnerable parameter (specific vector unknown).
3. The FortiSandbox system processes the crafted request without proper sanitization or validation.
4. The injected OS command is executed by the underlying operating system with the privileges of the FortiSandbox application.
5. The attacker leverages the command execution to install a reverse shell or other remote access tool.
6. The attacker establishes a persistent connection to the compromised system.
7. The attacker performs reconnaissance on the internal network.
8. The attacker moves laterally to other systems, exfiltrates sensitive data, or deploys malicious software.

Impact

Successful exploitation of CVE-2026-39808 allows an unauthenticated attacker to execute arbitrary commands on the FortiSandbox appliance. This can lead to full system compromise, potentially enabling data exfiltration, installation of malware, or disruption of services. Given a CVSS score of 9.8, the vulnerability is considered critical. The lack of specific attack vector details in the initial advisory makes mitigation challenging without vendor patches or workarounds.

Recommendation

• Monitor web server logs for suspicious requests targeting FortiSandbox instances (category: webserver, product: linux).
• Apply available patches or upgrades from Fortinet to address CVE-2026-39808 as soon as they are released.
• Inspect network traffic for unusual outbound connections originating from FortiSandbox appliances (category: network_connection, product: linux).
• Deploy the provided Sigma rule to detect potential exploitation attempts based on common OS command injection patterns.

Attack Chain

1. Attacker authenticates to the FortiDDoS-F appliance with valid low-privilege credentials.
2. Attacker crafts a malicious SQL query containing special characters designed to exploit the SQL injection vulnerability.
3. Attacker sends the crafted SQL query to the vulnerable FortiDDoS-F endpoint. (Attack Vector N/A from source)
4. The FortiDDoS-F appliance processes the malicious SQL query without proper sanitization.
5. The malicious SQL query is executed against the FortiDDoS-F database.
6. The attacker injects and executes arbitrary SQL code, potentially gaining access to sensitive data or the ability to modify system configurations.
7. The attacker leverages the injected SQL code to execute operating system commands on the FortiDDoS-F appliance.
8. The attacker escalates privileges and compromises the FortiDDoS-F system, potentially gaining complete control.

Impact

Successful exploitation of CVE-2026-39815 can lead to unauthorized code execution, sensitive data exposure, and complete system compromise of the Fortinet FortiDDoS-F appliance. While the number of potential victims is not specified, all organizations using Fortinet FortiDDoS-F versions 7.2.1 and 7.2.2 are vulnerable. A successful attack could disrupt network operations, compromise sensitive data, and allow attackers to use the FortiDDoS-F appliance as a pivot point for further attacks within the network.

Recommendation

• Upgrade Fortinet FortiDDoS-F installations to a patched version that addresses CVE-2026-39815.
• Monitor FortiDDoS-F systems for suspicious activity, including unusual SQL queries, leveraging the webserver log source to detect anomalous HTTP requests related to potential exploitation attempts.
• Deploy the Sigma rule Detect Suspicious FortiDDoS-F SQL Injection Attempts to your SIEM to detect potential exploitation attempts.

Attack Chain

1. An unauthenticated attacker sends a crafted request to the FortiSandbox appliance.
2. The request targets a specific endpoint vulnerable to path traversal.
3. The attacker includes the “../filedir” sequence within a file path parameter.
4. The vulnerable application fails to properly sanitize the file path.
5. The attacker uses path traversal to access sensitive configuration files or system binaries.
6. By overwriting existing system files, the attacker escalates privileges.
7. The attacker executes arbitrary commands with elevated privileges.
8. The attacker gains full control of the FortiSandbox appliance, potentially allowing lateral movement to other systems.

Impact

Successful exploitation of CVE-2026-39813 allows an unauthenticated attacker to escalate privileges on the Fortinet FortiSandbox appliance. This could lead to complete system compromise, sensitive data exfiltration, or the deployment of malicious payloads. The lack of specific victim numbers or sectors targeted in the source data prevents further quantitative assessment. However, given the appliance’s role in network security, a successful attack could severely impact the security posture of organizations using the vulnerable FortiSandbox versions.

Recommendation

• Upgrade Fortinet FortiSandbox to a patched version outside the vulnerable range (5.0.0-5.0.5 and 4.4.0-4.4.8) to remediate CVE-2026-39813.
• Deploy the Sigma rule “Detect Fortinet FortiSandbox Path Traversal Attempt” to identify exploitation attempts in web server logs.
• Monitor web server logs for suspicious requests containing “../filedir” patterns.
• Investigate any alerts generated by the Sigma rules and review system logs for signs of unauthorized access or privilege escalation.

Attack Chain

1. The attacker identifies a vulnerable FortiAnalyzer or FortiManager Cloud instance running versions 7.6.2-7.6.4.
2. The attacker crafts a malicious HTTP request designed to trigger the heap-based buffer overflow. This involves analyzing the vulnerable application to identify the specific request parameters and data structures that can be manipulated.
3. The attacker sends the crafted request to the targeted Fortinet Cloud instance.
4. Due to the buffer overflow, the crafted request overwrites adjacent memory on the heap, potentially corrupting data structures used by the application.
5. The attacker attempts to leverage the memory corruption to gain control of program execution. Because of ASLR, this step requires careful planning and potentially multiple attempts to bypass address randomization.
6. Upon successful bypass of ASLR, the attacker overwrites a function pointer or other critical data in memory to redirect program control to attacker-controlled code.
7. The attacker executes arbitrary code within the context of the FortiAnalyzer or FortiManager Cloud process.
8. The attacker can now execute commands, potentially gaining unauthorized access to sensitive data, modifying system configurations, or deploying further malicious payloads within the cloud environment.

Impact

Successful exploitation of CVE-2026-22828 can allow a remote, unauthenticated attacker to execute arbitrary code on vulnerable Fortinet FortiAnalyzer Cloud and FortiManager Cloud instances (versions 7.6.2 through 7.6.4). While the effort required is considerable, a successful attack can lead to a complete compromise of the affected system, potentially resulting in data breaches, service disruption, or the deployment of malicious software. The absence of specific victim counts or sector targeting details in the original advisory emphasizes the importance of proactive mitigation.

Recommendation

• Apply available patches or upgrade to a fixed version of Fortinet FortiAnalyzer Cloud and FortiManager Cloud to address CVE-2026-22828 (https://fortiguard.fortinet.com/psirt/FG-IR-26-121).
• Implement network segmentation to limit the potential impact of a successful exploit, as mentioned in the vulnerability description.
• Deploy the Sigma rule “Detect Suspicious HTTP Requests to Fortinet Cloud Services” to identify potential exploitation attempts (see rule below).

Attack Chain

1. The attacker identifies a vulnerable FortiClient EMS instance (versions 7.4.5 through 7.4.6) exposed on the network.
2. The attacker crafts a malicious HTTP/API request targeting the unauthenticated API interface of the FortiClient EMS.
3. The crafted request bypasses authentication and authorization checks due to improper access control (CWE-284).
4. The bypassed access controls allow the attacker to execute unauthorized code or commands on the EMS server.
5. The attacker obtains control of administrative functionality on the FortiClient EMS server.
6. The attacker manipulates or exfiltrates sensitive configuration and policy data stored on the EMS.
7. The attacker deploys malicious payloads to managed endpoints via the compromised EMS server.
8. The attacker uses the compromised EMS as a foothold for further network intrusion or lateral movement.

Impact

Successful exploitation of CVE-2026-35616 can lead to a full compromise of the FortiClient EMS infrastructure. This includes the ability to manipulate or exfiltrate sensitive configuration and policy data, corrupt or disable endpoint protections, disrupt endpoint management services, and deploy malicious payloads to managed endpoints. The vulnerability enables lateral movement across enterprise networks. The CCB has confirmed that this vulnerability has been exploited in the wild.

Recommendation

• Apply the latest Fortinet patch for FortiClient EMS to remediate CVE-2026-35616 immediately.
• Upscale monitoring and detection capabilities to identify any related suspicious activity, ensuring a swift response in case of an intrusion as recommended by the CCB.
• Deploy the Sigma rule detecting unauthorized API access to the FortiClient EMS webserver to your SIEM and tune for your environment.

Attack Chain

1. An unauthenticated attacker identifies a vulnerable FortiClient EMS server.
2. The attacker crafts a malicious API request designed to bypass authentication controls.
3. The crafted request exploits the improper access control vulnerability (CVE-2026-35616) in the API authentication process.
4. The vulnerable FortiClient EMS server processes the request without proper authentication.
5. The attacker injects and executes arbitrary code or commands on the FortiClient EMS server.
6. The attacker gains control of the FortiClient EMS server.
7. The attacker could leverage the compromised server to manage endpoints, deploy malicious software, or exfiltrate sensitive data.

Impact

Successful exploitation of CVE-2026-35616 allows unauthenticated remote attackers to execute arbitrary code or commands on a FortiClient EMS server. This could lead to full compromise of the server, potentially impacting hundreds or thousands of managed endpoints. Attackers could leverage this access to deploy ransomware, steal sensitive data, or disrupt business operations. The observed exploitation in the wild indicates a high risk of widespread attacks.

Recommendation

• Apply the Fortinet hotfix for CVE-2026-35616 to all FortiClient EMS servers immediately.
• Deploy the Sigma rules provided below to your SIEM to detect potential exploitation attempts.
• Monitor web server logs for unusual API requests targeting FortiClient EMS (see Sigma rules for examples).
• Enable logging on FortiClient EMS servers to facilitate investigation of potential incidents.