Fortinet FortiWeb CVE-2025-25257: Pre-Auth SQL Injection to RCE – Anatomy of a Critical WAF Compromise

When a web application firewall (WAF) becomes the attack vector, the stakes for enterprise security rise dramatically. In July 2025, threat actors began exploiting a critical flaw in Fortinet's FortiWeb appliances, compromising perimeter defenses and gaining remote code execution (RCE) without authentication. CVE-2025-25257 is not just another SQL injection—it's a blueprint for how a single pre-auth flaw can undermine the very systems designed to protect web infrastructure.

Introduction

Fortinet is a global powerhouse in network security, with its FortiWeb product line deployed across thousands of enterprise and government environments as a primary web application firewall (WAF). FortiWeb is engineered to defend critical web assets from OWASP Top 10 threats, DDoS, and zero-day exploits. With a customer base in the tens of thousands and a reputation for robust perimeter defense, vulnerabilities in FortiWeb have outsized impact—breaches here can expose sensitive data, SSL keys, and downstream systems across entire organizations.

Technical Information

CVE-2025-25257 is a textbook example of how improper input handling can cascade into catastrophic compromise. The vulnerability resides in the get_fabric_user_by_token() function within the Fabric Connector component of FortiWeb. This function processes incoming HTTP requests to the /api/fabric/device/status endpoint, extracting the Bearer token from the Authorization header. Critically, this token is interpolated directly into an SQL query without sufficient sanitization or parameterization.

Root Cause:

The SQL injection arises because user-supplied tokens are concatenated into SQL statements, allowing an attacker to inject arbitrary SQL. For example, a malicious request might look like:

POST /api/fabric/device/status HTTP/1.1
Host: <fortiweb-ip>
Authorization: Bearer 123'/**/or/**/'x'='x
Content-Type: application/json
Content-Length: ...

{"dummy":"data"}

This payload bypasses authentication by manipulating the SQL logic, exploiting the lack of neutralization for special characters (CWE-89).

Attack Vector and Exploitation:

Attackers exploit the SQLi to escalate privileges and achieve RCE by leveraging MySQL's INTO OUTFILE capability. By crafting a query that writes a Python .pth file to the server's site-packages directory, the attacker ensures that arbitrary Python code will be executed the next time the Python interpreter is invoked (for example, via /cgi-bin/ml-draw.py). This is possible because Python's site module automatically executes code in .pth files at startup. The attack chain is fully pre-auth and requires no user interaction.

Constraints and Evasion:

Exploitation payloads must avoid spaces and are often hex-encoded or use alternative whitespace representations to bypass input filters. Attackers have demonstrated the ability to evade basic WAF signatures and log tampering, making detection challenging without deep inspection of Authorization headers and file system changes.

Proof of Concept

The vulnerability in Fortinet's FortiWeb, identified as CVE-2025-25257, arises from improper handling of user input within the get_fabric_user_by_token() function. This function processes the Authorization header from incoming HTTP requests, specifically expecting a bearer token. However, it fails to adequately sanitize this input before incorporating it into an SQL query, leading to a SQL Injection (SQLi) vulnerability.

An attacker can exploit this flaw by sending a specially crafted HTTP request to the /api/fabric/device/status endpoint. By injecting malicious SQL code into the Authorization header, the attacker can manipulate the SQL query executed by the server. For instance, using a payload like Bearer 123'/**/or/**/'x'='x allows the attacker to bypass authentication checks. (pwner.gg)

To escalate this SQLi to remote code execution (RCE), the attacker can leverage MySQL's INTO OUTFILE statement, which permits writing files to the server's filesystem. By crafting a query that writes a Python .pth file containing malicious code into the Python site-packages directory, the attacker sets the stage for code execution. Subsequently, triggering a legitimate Python-based CGI script, such as /cgi-bin/ml-draw.py, causes the Python interpreter to execute the code within the .pth file, thereby achieving RCE. (pwner.gg)

This method exploits the automatic execution of .pth files by Python's site module during interpreter startup, allowing the injected code to run with the privileges of the Python process, which, in this case, are elevated due to the server's configuration. (pwner.gg)

Patch Information

To address the critical SQL injection vulnerability identified in FortiWeb (CVE-2025-25257), Fortinet has released specific updates for affected versions. It's essential to upgrade your FortiWeb installations to the following versions to mitigate this issue:

FortiWeb 7.6: Upgrade to version 7.6.4 or later.
FortiWeb 7.4: Upgrade to version 7.4.8 or later.
FortiWeb 7.2: Upgrade to version 7.2.11 or later.
FortiWeb 7.0: Upgrade to version 7.0.11 or later.

These updates rectify the improper neutralization of special elements used in SQL commands, thereby preventing unauthorized SQL code execution via crafted HTTP or HTTPS requests. (cert.europa.eu)

For detailed information and to download the necessary updates, please refer to Fortinet's official advisory: (cert.europa.eu)

Note: If immediate upgrading isn't feasible, consider disabling the HTTP/HTTPS administrative interface as a temporary mitigation measure. However, this should not replace the recommended software update.

Detection Methods

Detecting exploitation attempts of CVE-2025-25257 in Fortinet FortiWeb requires a multi-faceted approach, combining signature-based detection, behavioral analysis, and vigilant monitoring of system logs. Below are key strategies to identify potential indicators of compromise (IoCs) associated with this vulnerability:

1. Signature-Based Detection:

Implement intrusion detection and prevention systems (IDS/IPS) equipped with up-to-date signatures that can recognize patterns indicative of SQL injection attacks targeting FortiWeb's administrative interfaces. These signatures should specifically look for malicious payloads in HTTP Authorization headers, as the vulnerability exploits unsanitized Bearer tokens.

2. Behavioral Analysis:

Monitor for anomalous HTTP/HTTPS requests to the FortiWeb administrative GUI, particularly those directed at the /api/fabric/device/status endpoint. Unusual patterns, such as a high volume of requests or requests containing unexpected SQL syntax elements (e.g., single quotes, double dashes, or UNION statements), may indicate exploitation attempts.

3. Log Analysis:

Regularly review FortiWeb logs for signs of unauthorized access or configuration changes. Indicators include:

Unexpected entries in authentication logs, especially failed login attempts followed by successful ones.
Alterations in administrative settings or user accounts without corresponding legitimate administrative actions.
Presence of SQL error messages or stack traces in logs, which may suggest attempted or successful SQL injection attacks.

4. Network Traffic Monitoring:

Utilize network monitoring tools to detect unusual outbound traffic patterns from FortiWeb appliances. Anomalies may include:

Connections to unfamiliar IP addresses or domains.
Large data transfers that are inconsistent with normal operational behavior.

5. File Integrity Checks:

Conduct regular integrity checks on critical system files and directories. The exploitation of this vulnerability can lead to unauthorized file modifications or creations, such as the presence of unexpected scripts or executables in the /cgi-bin directory.

6. Endpoint Detection and Response (EDR):

Deploy EDR solutions to monitor for suspicious activities on the FortiWeb appliance, including:

Execution of unauthorized processes or scripts.
Changes to system configurations or registry entries that could indicate compromise.

7. Vulnerability Scanning:

Utilize vulnerability scanners to identify FortiWeb instances running affected versions. For example, Qualys provides QID 44706 to detect assets vulnerable to CVE-2025-25257. (threatprotect.qualys.com)

8. Threat Intelligence Feeds:

Subscribe to threat intelligence services to stay informed about emerging IoCs and tactics related to CVE-2025-25257. This proactive approach enables timely updates to detection mechanisms and response strategies.

By integrating these detection methods, organizations can enhance their ability to identify and respond to exploitation attempts targeting FortiWeb appliances, thereby mitigating potential risks associated with CVE-2025-25257.

Affected Systems and Versions

CVE-2025-25257 affects the following FortiWeb versions:

FortiWeb 7.6.0 through 7.6.3
FortiWeb 7.4.0 through 7.4.7
FortiWeb 7.2.0 through 7.2.10
FortiWeb versions below 7.0.11

All configurations exposing the administrative HTTP/HTTPS interface are vulnerable. Systems not upgraded to the fixed versions listed above remain at risk.

Vendor Security History

Fortinet has a history of critical vulnerabilities in its perimeter security products, including the FortiGate SSL-VPN flaws (e.g., CVE-2024-55591) and multiple high-severity issues in FortiOS and FortiWeb. While the company's patch response time has improved, the practice of silent patching—releasing fixes before public disclosure—has left customers exposed to zero-day exploitation windows, as seen with CVE-2025-25257. Security teams should monitor Fortinet advisories closely and prioritize rapid deployment of critical updates.

References

Source: This report was created using AI

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