CVE-2026-25815: FortiOS LDAP Credential Disclosure Flaw

CVE-2026-25815 Overview

A cryptographic vulnerability exists in Fortinet FortiOS through version 7.6.6 that allows attackers to decrypt LDAP credentials stored in device configuration files. This weakness stems from the use of a static, shared encryption key that is identical across all customer installations by default (CWE-1394: Use of Default Cryptographic Key). The vulnerability has been actively exploited in the wild from 2025-12-16 through 2026.

Critical Impact

Attackers with access to FortiOS configuration files can decrypt stored LDAP credentials, potentially compromising enterprise Active Directory environments and enabling lateral movement across networks.

Affected Products

• Fortinet FortiOS through version 7.6.6
• FortiGate devices using default encryption settings
• Environments with LDAP authentication configured on FortiOS appliances

Discovery Timeline

• 2025-12-16 - Active exploitation observed in the wild
• 2026-02-05 - CVE CVE-2026-25815 published to NVD
• 2026-02-05 - Last updated in NVD database

Technical Details for CVE-2026-25815

Vulnerability Analysis

This vulnerability is classified under CWE-1394 (Use of Default Cryptographic Key), representing a fundamental cryptographic design weakness in FortiOS's credential storage mechanism. The core issue is that LDAP credentials stored within device configuration files are encrypted using a static key that remains consistent across all FortiOS installations worldwide. This means any attacker who obtains a configuration backup—through configuration export, backup file theft, or other means—can decrypt the embedded LDAP credentials using the known default key.

According to CERT Austria's analysis, threat actors have been leveraging FortiCloud to collect LDAP connection passwords from vulnerable devices. The vendor's position is that this is not a vulnerability because customers "are supposed to enable" a non-default private data encryption option. However, this option can disrupt functionality as documented in Fortinet's own Managing FortiGates with private data encryption guide, which explains why it is intentionally not enabled by default.

Root Cause

The root cause is the use of a hardcoded, static encryption key for protecting sensitive credential data in FortiOS configuration files. Rather than generating unique per-device or per-customer encryption keys during installation or initial setup, FortiOS uses an identical key across all deployments. This design decision, likely made to simplify device management and configuration portability, creates a scenario where obtaining the encryption algorithm and key from one device enables decryption of credentials from any FortiOS installation.

Attack Vector

The attack requires local access to FortiOS configuration files, which can be obtained through several methods:

1. Configuration Backup Theft: Attackers compromise backup storage containing FortiOS configuration exports
2. FortiCloud Access: Leveraging compromised FortiCloud accounts to retrieve device configurations
3. Administrative Access: Gaining unauthorized admin access to FortiOS devices to export configurations
4. Man-in-the-Middle: Intercepting configuration transfers during backup operations

Once configuration files are obtained, the attacker extracts the encrypted LDAP credentials and decrypts them using the known default key. These credentials can then be used to authenticate to enterprise LDAP/Active Directory environments, potentially enabling domain compromise.

Detection Methods for CVE-2026-25815

Indicators of Compromise

• Unusual configuration export or backup activities on FortiOS devices
• Unexpected FortiCloud API calls retrieving device configurations
• Authentication attempts using LDAP credentials from previously secure FortiOS-managed accounts
• Unauthorized administrative sessions on FortiGate appliances

Detection Strategies

• Monitor FortiOS audit logs for configuration export events outside maintenance windows
• Implement alerting on FortiCloud account access patterns and configuration downloads
• Enable LDAP server logging to detect authentication attempts from unexpected sources
• Review FortiManager logs for bulk configuration retrieval activities

Monitoring Recommendations

• Establish baseline metrics for configuration backup frequency and alert on deviations
• Monitor network traffic for LDAP authentication attempts originating from non-FortiOS IP addresses using credentials stored in FortiOS
• Implement SIEM rules correlating FortiOS configuration access with subsequent LDAP authentication anomalies
• Audit FortiCloud access logs and enable multi-factor authentication for all cloud management accounts

How to Mitigate CVE-2026-25815

Immediate Actions Required

• Enable private data encryption on all FortiOS devices to use unique encryption keys
• Rotate all LDAP credentials currently stored in FortiOS configuration files
• Review FortiCloud access logs for unauthorized configuration downloads
• Audit backup storage security for FortiOS configuration files

Patch Information

Fortinet's official position is that this behavior is by design and customers should enable the private data encryption feature. Refer to the FortiManager Administration Guide for detailed instructions on enabling private data encryption. Note that enabling this feature may impact certain management operations and functionality, so thorough testing in a non-production environment is recommended before deployment.

Workarounds

• Enable private data encryption following Fortinet's documentation, accepting potential management functionality impacts
• Store FortiOS configuration backups in encrypted storage with strict access controls
• Implement network segmentation to limit exposure if LDAP credentials are compromised
• Consider using alternative authentication mechanisms that don't store credentials in device configurations

# Verify private data encryption status on FortiOS
# Connect to FortiOS CLI and check encryption configuration
config system global
    get private-data-encryption
end

# Enable private data encryption (requires careful planning)
config system global
    set private-data-encryption enable
end