CVE-2025-48826

Executive Summary

CVE-2025-48826 is a critical format string vulnerability in the formPingCmd functionality of the Planet WGR-500 router, firmware version v1.3411b190912. This vulnerability allows an unauthenticated, remote attacker to send a series of specially crafted HTTP requests, leading to memory corruption. With a CVSS score of 8.8, successful exploitation could result in arbitrary code execution, denial of service, or information disclosure. No public proof-of-concept (PoC) or exploit code is currently available, and no patch has been released by the vendor. The vulnerability is classified under CWE-134 (Use of Externally-Controlled Format String).

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a firmware-level issue in an embedded network device (Planet WGR-500 router). No supply chain package security implications apply.

CVSS Breakdown & Threat Level

• CVSS Score: 8.8 (High)
• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: None (PR:N)
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: High (C:H)
• Integrity Impact: High (I:H)
• Availability Impact: High (A:H)

Threat Level: Critical. The vulnerability is remotely exploitable without authentication, and the impact on confidentiality, integrity, and availability is high. The lack of a patch and the potential for memory corruption make this a high-priority target for threat actors.

Deep Dive & Mechanics

The vulnerability resides in the formPingCmd function, which is part of the router's web management interface. This function is responsible for handling ping commands sent via HTTP POST requests. The flaw is a classic format string vulnerability: user-supplied input is passed directly as the format string argument to a function like printf or sprintf, without proper sanitization.

Mechanism:

1. An attacker sends a series of HTTP requests to the vulnerable endpoint (e.g., /goform/formPingCmd).
2. The formPingCmd function receives the ping_addr parameter (or similar) from the request.
3. This parameter is used directly in a format string function (e.g., sprintf(buffer, user_input)).
4. By including format specifiers like %x, %n, %s, or %p in the input, the attacker can read from or write to arbitrary memory locations.
5. Over multiple requests, the attacker can achieve memory corruption, potentially leading to arbitrary code execution.

Attack Vector: Remote, unauthenticated HTTP requests to the router's web interface.

Prerequisites: The attacker must have network access to the router's management interface (typically port 80 or 443).

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is the only reference. The following is a hypothetical representation of the vulnerable code and a patched version.

Vulnerable Code (C-like pseudocode):

void formPingCmd(struct request *req) {
    char buffer[256];
    char *ping_addr = get_param(req, "ping_addr");
    // VULNERABLE: user input used as format string
    sprintf(buffer, ping_addr);
    system(buffer);
}

Patched Code (Hypothetical):

void formPingCmd(struct request *req) {
    char buffer[256];
    char *ping_addr = get_param(req, "ping_addr");
    // PATCHED: use %s format specifier
    sprintf(buffer, "%s", ping_addr);
    // Additional input validation
    if (!is_valid_ip(ping_addr)) {
        return_error(req);
        return;
    }
    system(buffer);
}

The key difference is the use of "%s" as the format string, which prevents the attacker from injecting format specifiers.

Exploitation & Lab Setup

Red Team (Exploitation)

Objective: Achieve remote code execution on the Planet WGR-500 router.

Lab Setup:

• Target: Planet WGR-500 router with firmware v1.3411b190912.
• Attacker: Kali Linux machine on the same network.
• Tools: curl, python3, pwntools (for exploit development).

Exploitation Steps (Conceptual):

1. Identify the vulnerable endpoint: Send a POST request to /goform/formPingCmd with a ping_addr parameter.
2. Craft format string payload: Use format specifiers to leak memory addresses (e.g., %p.%p.%p) and then overwrite a GOT entry or return address.
3. Send multiple requests: Use a series of requests to gradually corrupt memory and achieve code execution.
4. Execute shellcode: Overwrite a function pointer with the address of shellcode that spawns a reverse shell.

Example curl command to test for vulnerability:

curl -X POST http://<router_ip>/goform/formPingCmd -d "ping_addr=%x.%x.%x"

Note: No public exploit code is available. The above is a conceptual approach.

Blue Team (Defense)

Detection:

• Monitor HTTP POST requests to /goform/formPingCmd containing format specifiers (%x, %n, %s, %p).
• Look for anomalous patterns in the ping_addr parameter (e.g., long strings, non-IP characters).
• Use network intrusion detection systems (NIDS) to alert on format string patterns.

Mitigation:

• Isolate the router's management interface from untrusted networks (e.g., use a VLAN or firewall rules).
• Disable remote management if not required.
• Apply vendor patches as soon as they become available.
• Implement input validation and sanitization at the application layer (e.g., reject non-IP input).

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP POST requests to /goform/formPingCmd with ping_addr containing % characters.
  • Repeated requests with varying format specifiers.
  • Unusual outbound connections from the router (e.g., to attacker-controlled IPs on non-standard ports).
• Host IOCs:
  • Unexpected processes running on the router (if shell access is obtained).
  • Modified firmware or configuration files.
  • Log entries showing failed ping commands or memory errors.

Detection Engineering

YARA Rule

rule CVE_2025_48826_FormatString {
    meta:
        description = "Detects format string attempts against Planet WGR-500 formPingCmd"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-48826"
    strings:
        $format_specifier = /%[ndiusxXcsp]/
        $endpoint = "/goform/formPingCmd"
    condition:
        $endpoint and #format_specifier > 2
}

Sigma Rule

title: CVE-2025-48826 Format String Attempt on Planet WGR-500
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects HTTP POST requests to /goform/formPingCmd with format specifiers
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: 
            - '%x'
            - '%n'
            - '%s'
            - '%p'
    condition: selection
falsepositives:
    - Legitimate ping commands with IP addresses containing '%' (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-48826 Format String Attempt on Planet WGR-500"; flow:to_server; content:"POST"; http_method; content:"/goform/formPingCmd"; http_uri; pcre:"/(%[ndiusxXcsp])/"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate the device: Place the Planet WGR-500 router behind a firewall and restrict access to the management interface to trusted IPs only.
2. Disable remote management: If not required, disable the web management interface or restrict it to local network access.
3. Monitor logs: Enable logging and monitor for suspicious HTTP requests to /goform/formPingCmd.

Long-Term Actions:

1. Vendor patch: Contact Planet for a firmware update. If no patch is available, consider replacing the device.
2. Input validation: If source code access is available, implement proper format string handling (use "%s" instead of direct user input).
3. Network segmentation: Place IoT devices like routers in a separate VLAN with limited internet access.

Workarounds:

• Use a reverse proxy or WAF to filter requests containing format specifiers.
• Implement custom firewall rules to block POST requests to /goform/formPingCmd from untrusted sources.

Valters IT
Securing Digital Frontiers