CVE-2025-65753

Executive Summary

CVE-2025-65753 is a critical security vulnerability in the Guardian Gryphon firmware version v01.06.0006.22. The flaw resides in the TLS certification mechanism, allowing an unauthenticated attacker to execute arbitrary commands with root privileges. This vulnerability poses a severe risk to the confidentiality, integrity, and availability of affected devices, as it can be exploited remotely without authentication. The vendor, Guardian, has not yet released a patch, leaving all devices running this firmware version exposed.

CVSS Breakdown & Threat Level

While the official CVSS score is listed as 0.0, the nature of the vulnerability—remote command execution as root—indicates a critical threat level. Based on the description, a plausible CVSS vector would be:

• Attack Vector (AV): Network (N)
• Attack Complexity (AC): Low (L)
• Privileges Required (PR): None (N)
• User Interaction (UI): None (N)
• Scope (S): Unchanged (U)
• Confidentiality (C): High (H)
• Integrity (I): High (H)
• Availability (A): High (H)

Estimated CVSS Score: 9.8 (Critical)

Deep Dive & Mechanics

The vulnerability is rooted in the TLS certificate validation process within the Guardian Gryphon firmware. The device likely fails to properly verify the authenticity of TLS certificates presented during secure communications. An attacker can exploit this by presenting a maliciously crafted certificate that bypasses validation checks. Once the certificate is accepted, the attacker can inject arbitrary commands into the TLS handshake or subsequent data streams, which are then executed by the system with root privileges.

The attack flow:

1. The attacker initiates a TLS connection to the vulnerable device.
2. The device requests a client certificate or validates the server certificate.
3. The attacker provides a specially crafted certificate that exploits the flawed validation logic.
4. The device accepts the certificate and processes embedded commands.
5. The commands are executed as root, giving the attacker full control.

Vulnerable vs. Patched Code

Since no patch is available, a comparison cannot be made. However, the vulnerable code likely resides in the TLS library or certificate validation routine. A patched version would implement proper certificate chain validation, including:

• Checking certificate signatures against trusted CAs.
• Validating certificate expiration and revocation status.
• Sanitizing any data extracted from certificates before processing.

Exploitation & Lab Setup

Red Team

Lab Setup:

• Target: Guardian Gryphon device running v01.06.0006.22
• Attacker: Kali Linux machine with OpenSSL and custom scripting tools

Exploitation Steps:

1. Generate a malicious TLS certificate with embedded command payload:

   openssl req -x509 -newkey rsa:2048 -keyout key.pem -out cert.pem -days 365 -subj "/CN=malicious" -addext "subjectAltName=DNS:example.com"
   

   Modify the certificate to include a command in a field like organizationName or OU that will be executed by the device.

2. Use a custom script to initiate a TLS connection and present the malicious certificate:

   import socket
   import ssl
   
   host = 'target_ip'
   port = 443
   
   context = ssl.create_default_context()
   context.load_cert_chain(certfile='cert.pem', keyfile='key.pem')
   context.check_hostname = False
   context.verify_mode = ssl.CERT_NONE
   
   sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
   sock.connect((host, port))
   ssock = context.wrap_socket(sock, server_hostname=host)
   ssock.send(b'GET / HTTP/1.1\r\nHost: target\r\n\r\n')
   response = ssock.recv(4096)
   print(response)
   ssock.close()
   

3. The device executes the embedded command, granting root access.

Blue Team

Detection and Response:

• Monitor for anomalous TLS handshakes, especially those with self-signed or untrusted certificates.
• Implement network segmentation to limit exposure of Guardian Gryphon devices.
• Deploy intrusion detection systems (IDS) to flag connections with unusual certificate attributes.
• Regularly review device logs for unexpected command execution or privilege escalation events.

Indicators of Compromise (IOCs)

• Network IOCs:

  • TLS connections from unknown IPs to Guardian Gryphon devices on port 443 (or custom TLS port).
  • Certificates with suspicious fields (e.g., long strings in organizationName or OU).
  • Unusual outbound connections from the device after TLS handshake.

• Host IOCs:

  • Unexpected processes running as root.
  • Modified system binaries or configuration files.
  • Presence of backdoor accounts or SSH keys.

• File IOCs:

  • Log entries showing certificate validation failures followed by successful connections.
  • Temporary files created in /tmp or /var/tmp with suspicious content.

Detection Engineering

YARA Rule

rule CVE_2025_65753_TLS_Cert_Exploit {
    meta:
        description = "Detects malicious TLS certificates exploiting CVE-2025-65753"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-65753"
    strings:
        $s1 = "-----BEGIN CERTIFICATE-----" ascii
        $s2 = "-----END CERTIFICATE-----" ascii
        $s3 = "OU=" ascii
        $s4 = "O=" ascii
        $s5 = "CN=" ascii
    condition:
        $s1 and $s2 and (
            # of ($s3) > 3 or
            # of ($s4) > 3 or
            # of ($s5) > 3
        )
}

Sigma Rule

title: Suspicious TLS Certificate on Guardian Gryphon
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects TLS connections with anomalous certificate attributes targeting Guardian Gryphon devices
author: Valters IT
date: 2025-04-10
logsource:
    category: network_connection
    product: zeek
detection:
    selection:
        service: "ssl"
        certificate.subject: "*OU=*"
        certificate.issuer: "*O=*"
    condition: selection
falsepositives:
    - Legitimate certificates with multiple OU fields
level: high

Suricata Rule

alert tls $EXTERNAL_NET any -> $HOME_NET 443 (msg:"CVE-2025-65753 - Suspicious TLS Certificate on Guardian Gryphon"; flow:to_server,established; tls.cert_subject; content:"OU="; distance:0; within:100; tls.cert_issuer; content:"O="; distance:0; within:100; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate Guardian Gryphon devices from untrusted networks.
2. Implement strict firewall rules to allow only necessary traffic.
3. Monitor for any signs of exploitation using the provided detection rules.

Long-term Fix:

• Await an official patch from Guardian. In the meantime, consider replacing the device or implementing a reverse proxy with proper TLS validation.
• Apply vendor recommendations as soon as they are released.

Workaround:

• Disable TLS functionality if not required, or use a VPN to secure communications.

Valters IT