1. The Patient

Target: Fortinet FortiWeb Component: fwbcgi (Administrative CGI Binary) Vector: HTTP POST (Remote)

FortiWeb is positioned as the shield for critical assets—a Web Application Firewall (WAF) designed to filter malicious traffic. However, internally, it relies on a legacy architecture: Apache coupled with CGI binaries, a model dating back decades.

The security model relied on two fatal assumptions:

1. Requests reaching the internal CGI handlers are trusted.
2. Specific headers (like CGIINFO) originate only from internal IPC components.

These assumptions crumbled when exposed to the public internet, leading to a CVSS 9.8 collapse.

The Context: This is a dual-failure chain. CVE-2025-64446 allows an attacker to bypass authentication entirely by forging internal headers. CVE-2025-58034 then leverages that fake identity to inject shell commands into the policy management engine.

2. The Diagnosis

Root Cause: Full Authentication Collapse via Trust Boundary Violation.

The vulnerability stems from Path Resolution issues in Apache and Implicit Trust in the fwbcgi binary.

Part 1: The Authentication Mirage (CVE-2025-64446)

Legitimate API endpoints live under /api/v2.0/cmdb/. Apache processes the URL path before enforcing logical boundaries. By using path traversal (../), an attacker can escape the API logic and invoke fwbcgi directly.

Once inside, fwbcgi calls cgi_auth(). Instead of checking a database or a cryptographic session token, it looks for a header named CGIINFO.

• The Logic: If CGIINFO exists, the system Base64-decodes it, parses the JSON, and “hydrates” the user session based on the data inside.
• The Failure: There is no cryptographic signature. If the attacker sends this header, they become the Admin.

Part 2: The Command Injection (CVE-2025-58034)

Once authenticated as a fake Admin, the attacker targets the policy_scripting_post_handler. This handler is responsible for creating automation scripts. It constructs a shell command to invoke an underlying OS utility: /usr/local/bin/run_script --name <user_input>

The handler builds this command using string concatenation rather than argument vectors. It inserts user-controlled JSON fields (like name or script) verbatim.

3. The Kill-Chain

Phase 1: Path Traversal

The attacker bypasses the application layer routing by sending a request that traverses out of the API directory: POST /api/v2.0/cmdb/system/admin/../../../../../cgi-bin/fwbcgi

Phase 2: Identity Forgery

The attacker injects the malicious CGIINFO header to forge a Super-Admin identity:

{
  "username": "admin",
  "profname": "super_admin",
  "vdom": "root",
  "loginname": "admin"
}

fwbcgi trusts this input blindly and grants full privileges.

Phase 3: OS Command Injection

With Admin access, the attacker sends a payload to the scripting handler: name = "test; /bin/sh -c 'id'"

The server executes:

1. /usr/local/bin/run_script --name test (Legitimate)
2. /bin/sh -c 'id' (Malicious)

Impact: The attacker gains Remote Code Execution (RCE) as Root (UID 0). Because the appliance has no privilege separation, no chroot, and no seccomp filters, the compromise is total.

Phase 4: Post-Exploitation

Forensic analysis indicates this vector was used as a beachhead to attack downstream infrastructure, including the Cisco AsyncOS appliances detailed in AOAB #6.

4. The Fix

The remediation requires enforcing strict boundaries at the web server level and removing shell invocation from the code.

Vulnerable Logic (C++):

// FATAL: String concatenation allows shell metacharacters (; | &)
std::string cmd = "/usr/local/bin/run_script --name " + user_input;
system(cmd.c_str());

Patched Logic (C++):

// SECURITY FIX: Use execve/fork with an argument array.
// The shell is never invoked, so '; id' is treated as a filename, not a command.
char *args[] = {"/usr/local/bin/run_script", "--name", user_input.c_str(), NULL};
execve(args[0], args, env);

Developer Takeaway

Trust is not a boundary. Headers are user input, not a trust signal. Assuming that “only internal components set this header” is a fatal flaw in any internet-facing device. Furthermore, CGI is not sandboxed. It executes with ambient privilege. Systems must be designed to assume hostile traffic by default, verifying every claim of identity cryptographically.

Immediate Action:

1. Patch: Upgrade to FortiWeb 8.0.2+.
2. Mitigate: Restrict access to the management interface.
3. Sanitize: Ensure upstream load balancers block requests containing /cgi-bin/ in the URL path.