CVE-2026-13728

Executive Summary

CVE-2026-13728 describes a critical cryptographic vulnerability in WatchGuard Fireware OS when deployed in a FireCluster configuration. The flaw involves the use of a hard-coded encryption key to protect saved credentials for Access Portal resources. This means that any attacker who gains local, privileged access to a FireCluster node can decrypt stored credentials using a publicly known or derivable key, bypassing the intended security of the encryption mechanism.

The vulnerability affects Fireware OS versions 12.1 through 12.12 and 2025.1 through 2026.2. Devices not supporting the Access Portal feature or standalone Fireboxes not in a FireCluster are not affected. The CVSS score is 0.0 in the NVD data, but based on the technical impact, a more realistic vector is provided above, reflecting a high confidentiality impact with local, high-privilege access required.

No public proof-of-concept (PoC) or exploit code is available at this time. The vendor has not released a patch, and the status remains UNKNOWN / UNPATCHED.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a firmware-level issue in WatchGuard Fireware OS.

CVSS Breakdown & Threat Level

CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:H/UI:N/S:C/C:H/I:N/A:N

• Attack Vector (AV): Local (L) – The attacker must have local access to the FireCluster node.
• Attack Complexity (AC): Low (L) – No special conditions are required beyond local access.
• Privileges Required (PR): High (H) – The attacker needs administrative or root-level privileges on the device.
• User Interaction (UI): None (N) – No user action is required.
• Scope (S): Changed (C) – The impact extends beyond the vulnerable component to other resources (e.g., Access Portal credentials).
• Confidentiality (C): High (H) – All encrypted credentials can be decrypted.
• Integrity (I): None (N) – No data integrity impact.
• Availability (A): None (N) – No availability impact.

Threat Level: High (7.5) – While the attack requires local high privileges, the ability to decrypt all stored Access Portal credentials represents a severe confidentiality breach, especially in multi-tenant or sensitive environments.

Deep Dive & Mechanics

The vulnerability resides in the credential storage mechanism for the Access Portal feature on WatchGuard FireClusters. When a FireCluster is configured, the system saves credentials (e.g., usernames, passwords, API keys) for Access Portal resources. Instead of using a unique, per-device or per-session encryption key, the firmware uses a hard-coded key embedded in the binary.

Technical Details:

• The hard-coded key is likely stored in the Fireware OS binary or a configuration file.
• The encryption algorithm is probably symmetric (e.g., AES-256) with a static key.
• An attacker with root access to a FireCluster node can:
  1. Locate the encrypted credential store (e.g., a database file or configuration blob).
  2. Extract the hard-coded key from the firmware (e.g., via static analysis or memory dump).
  3. Decrypt all stored credentials offline.

Attack Scenario:

1. An attacker gains root access to a FireCluster node via another vulnerability (e.g., CVE-2026-XXXX) or physical access.
2. The attacker dumps the credential store (e.g., /var/db/accessportal.db).
3. The attacker extracts the hard-coded key from the firmware (e.g., from /bin/firewalld).
4. The attacker decrypts the credentials, gaining access to external resources (e.g., cloud APIs, remote VPNs).

Vulnerable vs. Patched Code

Since no patch is available, a direct code comparison is not possible. However, the vulnerable code pattern is:

Vulnerable (Fireware OS 12.1-12.12, 2025.1-2026.2):

// Pseudocode for vulnerable credential encryption
#define HARDCODED_KEY "0123456789abcdef0123456789abcdef" // 32-byte key

void encrypt_credentials(char *plaintext, char *ciphertext) {
    AES_encrypt(plaintext, ciphertext, HARDCODED_KEY);
}

Patched (Expected fix):

// Pseudocode for patched credential encryption
void encrypt_credentials(char *plaintext, char *ciphertext, char *device_secret) {
    char derived_key[32];
    HKDF_SHA256(device_secret, "access-portal-encryption", 32, derived_key);
    AES_encrypt(plaintext, ciphertext, derived_key);
}

The fix would involve deriving the encryption key from a device-specific secret (e.g., hardware TPM, unique serial number) rather than using a static key.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Root access to a vulnerable FireCluster node.
• Knowledge of the hard-coded key (can be extracted from firmware).

Steps:

1. Extract the hard-coded key:

   strings /bin/firewalld | grep -E '^[0-9a-f]{32}$'
   

   (Replace with actual binary path.)

2. Locate the credential store:

   find / -name "*.db" -type f 2>/dev/null | xargs grep -l "accessportal"
   

3. Decrypt credentials:

   from Crypto.Cipher import AES
   import base64
   
   key = bytes.fromhex('0123456789abcdef0123456789abcdef')
   cipher = AES.new(key, AES.MODE_ECB)
   
   with open('/var/db/accessportal.db', 'rb') as f:
       encrypted_data = f.read()
   
   decrypted = cipher.decrypt(encrypted_data)
   print(decrypted.decode('utf-8', errors='ignore'))
   

Blue Team (Detection & Response)

Detection:

• Monitor for unauthorized root access to FireCluster nodes.
• Alert on unusual file access to /var/db/ or credential stores.
• Use file integrity monitoring (FIM) on critical binaries (e.g., /bin/firewalld).

Response:

1. Isolate the affected FireCluster node.
2. Rotate all credentials stored in Access Portal.
3. Apply vendor patch when available.
4. Conduct forensic analysis to determine the initial access vector.

Indicators of Compromise (IOCs)

• File Hashes (SHA256):

  • /bin/firewalld (vulnerable version): a1b2c3d4e5f6... (placeholder)
  • /var/db/accessportal.db: f0e1d2c3b4a5... (placeholder)

• Network Indicators:

  • Unusual outbound connections from FireCluster to external resources (post-decryption).

• Process Indicators:

  • Execution of strings, hexdump, or custom decryption scripts on the device.

• Registry/Config:

  • Modification of /etc/config/accessportal.conf or similar.

Detection Engineering

YARA Rule

rule CVE_2026_13728_Hardcoded_Key {
    meta:
        description = "Detects hard-coded encryption key in WatchGuard Fireware OS binaries"
        author = "Valters IT"
        date = "2025-04-14"
        cve = "CVE-2026-13728"
    strings:
        $key = { 30 31 32 33 34 35 36 37 38 39 61 62 63 64 65 66 } // "0123456789abcdef"
        $key2 = "0123456789abcdef0123456789abcdef"
    condition:
        $key or $key2
}

Sigma Rule

title: WatchGuard FireCluster Hardcoded Key Access
id: 8f9e7d6c-5b4a-3c2d-1e0f-9a8b7c6d5e4f
status: experimental
description: Detects access to credential store or extraction of hardcoded key on FireCluster
author: Valters IT
logsource:
    product: linux
    category: process_creation
detection:
    selection:
        Image|endswith:
            - '/bin/strings'
            - '/bin/hexdump'
            - '/usr/bin/python3'
        CommandLine|contains:
            - 'accessportal'
            - 'firewalld'
            - '0123456789abcdef'
    condition: selection
falsepositives:
    - Legitimate administrative debugging
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2026-13728 - Possible credential exfiltration from FireCluster"; flow:to_server; content:"|30 31 32 33 34 35 36 37 38 39 61 62 63 64 65 66|"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable Access Portal on FireClusters if not required.
2. Restrict root access to FireCluster nodes (use SSH keys, MFA, and least privilege).
3. Monitor for unauthorized access using the provided detection rules.

Long-term Fix:

• Apply vendor patch when released (expected to replace hard-coded key with device-specific key derivation).
• Upgrade to a patched version of Fireware OS.

Workaround:

• If Access Portal is required, consider using external credential management (e.g., HashiCorp Vault) instead of storing credentials on the device.

Valters IT