CVE-2025-54402

Executive Summary

CVE-2025-54402 is a critical stack-based buffer overflow vulnerability in the Planet WGR-500 router firmware version v1.3411b190912. The flaw resides in the formPingCmd functionality, specifically within the handling of the submit-url and ipaddr HTTP request parameters. An unauthenticated attacker can send a series of specially crafted HTTP requests to trigger a stack-based buffer overflow, potentially leading to remote code execution (RCE) and full device compromise. The CVSS score of 8.8 (High) reflects the ease of exploitation (network-based, low complexity, no privileges required) and the severe impact on confidentiality, integrity, and availability. No public proof-of-concept (PoC) or patch is currently available, making this a high-priority zero-day threat for affected devices.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – Exploitable remotely over the network.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – Exploit does not affect other components.
• Confidentiality (C): High (H) – Full data access possible.
• Integrity (I): High (H) – Full control over device data.
• Availability (A): High (H) – Potential denial of service or full compromise.

Threat Level: Critical. The vulnerability is remotely exploitable without authentication, and the lack of a patch increases risk. EPSS score is 0.0% (low exploitation likelihood currently), but this may change as details emerge.

Deep Dive & Mechanics

The vulnerability is a classic stack-based buffer overflow in the formPingCmd CGI handler of the Planet WGR-500 router. The submit-url and ipaddr parameters are copied into fixed-size stack buffers without proper bounds checking. By sending a series of HTTP requests with oversized values in these parameters, an attacker can overwrite the stack return address and other critical data.

Technical Details:

• The vulnerable function likely uses strcpy() or sprintf() without length validation.
• The overflow occurs when concatenating or processing the submit-url and ipaddr parameters.
• A series of requests is needed because the overflow may require multiple writes to bypass stack canaries or fill buffers.
• Successful exploitation can lead to arbitrary code execution in the context of the web server (typically root).

Attack Flow:

1. Attacker sends HTTP POST request to /goform/formPingCmd with crafted submit-url and ipaddr parameters.
2. The router processes the request, copying the parameters into stack buffers.
3. The overflow overwrites the return address and possibly other stack frames.
4. After multiple requests, the attacker gains control of the program counter.
5. Shellcode or ROP chain executes, providing a reverse shell or other payload.

Vulnerable vs. Patched Code

Since no patch is available, a hypothetical fix would involve:

• Replacing unsafe functions like strcpy() with strncpy() or using safe string handling.
• Adding input validation to limit parameter lengths.
• Implementing stack canaries and ASLR.

Vulnerable Code (Hypothetical):

void formPingCmd() {
    char submit_url[64];
    char ipaddr[64];
    char buffer[128];
    
    get_param("submit-url", submit_url);
    get_param("ipaddr", ipaddr);
    sprintf(buffer, "ping -c 4 %s %s", ipaddr, submit_url); // Overflow
    system(buffer);
}

Patched Code (Hypothetical):

void formPingCmd() {
    char submit_url[64];
    char ipaddr[64];
    char buffer[128];
    
    get_param_safe("submit-url", submit_url, sizeof(submit_url));
    get_param_safe("ipaddr", ipaddr, sizeof(ipaddr));
    snprintf(buffer, sizeof(buffer), "ping -c 4 %s %s", ipaddr, submit_url);
    system(buffer);
}

Exploitation & Lab Setup

Red Team (Offensive)

Lab Environment:

• Target: Planet WGR-500 router (firmware v1.3411b190912)
• Attacker: Kali Linux VM with network access to the router's management interface (typically 192.168.1.1)

Exploitation Steps:

1. Identify the router's IP and ensure the web interface is accessible.
2. Craft a Python script to send a series of HTTP POST requests with oversized submit-url and ipaddr parameters.
3. Use a pattern to determine the exact offset for overwriting the return address.
4. Generate shellcode (e.g., reverse shell) and embed it in the payload.
5. Execute the exploit to gain a root shell.

Example Exploit Snippet (Python):

import requests

target = "http://192.168.1.1/goform/formPingCmd"
payload = "A" * 200  # Overflow buffer
data = {
    "submit-url": payload,
    "ipaddr": payload
}
for i in range(5):  # Multiple requests to trigger overflow
    requests.post(target, data=data)

Note: No public exploit code is available; this is a conceptual example.

Blue Team (Defensive)

Detection & Response:

• Monitor for anomalous HTTP requests to /goform/formPingCmd with unusually long parameters.
• Implement network segmentation to isolate router management interfaces.
• Deploy WAF rules to block requests with parameter lengths exceeding expected limits.
• Use host-based IDS to detect abnormal process behavior (e.g., ping command with unexpected arguments).

Indicators of Compromise (IOCs)

• Network IOCs:

  • HTTP POST requests to /goform/formPingCmd with parameters exceeding 64 characters.
  • Repeated requests from the same source IP within a short time window.
  • Outbound connections from the router to unknown IPs on non-standard ports (e.g., 4444 for reverse shell).

• Host IOCs:

  • Unusual processes spawned by the web server (e.g., /bin/sh or reverse shell).
  • Modified firmware files or unexpected binaries in /tmp.
  • Stack traces in logs indicating buffer overflow (e.g., segmentation faults).

• File IOCs:

  • Suspicious files in /tmp with executable permissions.
  • Modified CGI binaries (e.g., formPingCmd).

Detection Engineering

YARA Rule

rule CVE_2025_54402_Planet_WGR500_Overflow {
    meta:
        description = "Detects exploit attempts for CVE-2025-54402 in HTTP requests"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-54402"
    strings:
        $s1 = "submit-url" ascii wide nocase
        $s2 = "ipaddr" ascii wide nocase
        $s3 = "formPingCmd" ascii wide nocase
        $overflow = { 41 41 41 41 41 41 41 41 } // Pattern of 'A's
    condition:
        all of ($s*) and #overflow > 10
}

Sigma Rule

title: CVE-2025-54402 Planet WGR-500 Buffer Overflow Attempt
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects HTTP POST requests with long parameters to formPingCmd
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/goform/formPingCmd'
        cs-uri-query|contains: 
            - 'submit-url'
            - 'ipaddr'
    condition: selection and (len(cs-uri-query) > 200)
falsepositives:
    - Legitimate long URLs (unlikely)
level: high

Suricata Rule

alert http $EXTERNAL_NET any -> $HOME_NET any (msg:"CVE-2025-54402 Planet WGR-500 Buffer Overflow Attempt"; flow:to_server,established; content:"POST"; http_method; content:"/goform/formPingCmd"; http_uri; content:"submit-url"; http_client_body; content:"ipaddr"; http_client_body; pcre:"/submit-url=[^&]{100,}/Pi"; pcre:"/ipaddr=[^&]{100,}/Pi"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate affected devices: Place Planet WGR-500 routers on a separate VLAN with strict access controls.
2. Disable remote management: If not required, disable the web interface or restrict access to trusted IPs.
3. Monitor logs: Enable logging and monitor for suspicious HTTP requests to /goform/formPingCmd.

Long-term Fixes:

• Vendor patch: Await an official firmware update from Planet. Contact vendor support for ETA.
• Workaround: If possible, replace the device with a patched alternative.
• Network segmentation: Implement strict firewall rules to limit exposure.

Valters IT Recommendations:

• Conduct a full network scan to identify all affected devices.
• Implement a Web Application Firewall (WAF) with custom rules to block oversized parameters.
• Educate users on the risks of exposing router management interfaces to the internet.

Report generated by Valters IT DevSecOps & CTI Expert System