CVE-2024-26342

Executive Summary

CVE-2024-26342 is a denial-of-service (DoS) vulnerability in the ASUS AC68U router firmware version 3.0.0.4.384.82230. The flaw resides in the /usr/sbin/httpd binary, where a null pointer dereference can be triggered by a specially crafted network packet sent by a remote, unauthenticated attacker. Successful exploitation causes the HTTP daemon to crash, rendering the router's web management interface unavailable. No public exploit code or proof-of-concept has been released, and no official patch is currently available from ASUS. The vulnerability is classified under MITRE ATT&CK tactic T1499 (Endpoint Denial of Service) and CWE-476 (NULL Pointer Dereference).

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, indicating that no official CVSS vector has been assigned by NVD. Based on the description and impact, a reasonable estimated CVSS v3.1 vector would be:

Estimated CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Estimated Base Score: 7.5 (High)

Breakdown:

• Attack Vector (AV): Network – the attacker can send packets remotely.
• Attack Complexity (AC): Low – no special conditions required.
• Privileges Required (PR): None – no authentication needed.
• User Interaction (UI): None – no user action required.
• Scope (S): Unchanged – the vulnerable component is the only affected system.
• Confidentiality (C): None – no data exposure.
• Integrity (I): None – no data modification.
• Availability (A): High – the HTTP service is completely disrupted.

Threat Level: High – the vulnerability is remotely exploitable without authentication and can cause a complete denial of service on the router's management interface.

Deep Dive & Mechanics

The vulnerability is a classic null pointer dereference in the HTTP daemon (httpd) of the ASUS AC68U router. The httpd process handles incoming HTTP requests for the router's web administration panel. When a specially crafted network packet is received, the code attempts to dereference a pointer that has not been properly initialized or has been set to NULL. This typically occurs in a function that parses HTTP headers, URI parameters, or other request components.

Root Cause Analysis:

• The vulnerable code path likely involves a conditional check that fails to validate a pointer before using it.
• For example, a function may allocate a buffer or structure based on a request parameter, but if the parameter is missing or malformed, the pointer remains NULL.
• When the code later attempts to read from or write to that pointer, the operating system raises a segmentation fault, crashing the httpd process.

Attack Vector:

• The attacker sends a single TCP packet (or a series of packets) to port 80 or 443 of the router.
• The packet contains a malformed HTTP request that triggers the null pointer dereference.
• No authentication is required, and the attack can be launched from anywhere on the network (including the internet if the router's web interface is exposed).

Impact:

• The httpd process crashes, making the web management interface unavailable.
• The router may automatically restart the httpd process (via a watchdog or init system), but repeated attacks can cause persistent DoS.
• Other router functions (routing, firewall, etc.) are not directly affected, but the loss of management access hinders administrative tasks.

Vulnerable vs. Patched Code

Since no patch is available, a direct code comparison cannot be made. However, based on the vulnerability type, the fix would involve adding a null pointer check before dereferencing the pointer in the affected code path.

Vulnerable Code (Hypothetical):

void handle_request(struct http_request *req) {
    char *param = get_parameter(req, "param_name");
    // No null check
    int len = strlen(param);  // NULL pointer dereference if param is NULL
    // ... rest of processing
}

Patched Code (Hypothetical):

void handle_request(struct http_request *req) {
    char *param = get_parameter(req, "param_name");
    if (param == NULL) {
        // Handle missing parameter gracefully
        send_error_response(req, 400, "Bad Request");
        return;
    }
    int len = strlen(param);
    // ... rest of processing
}

The patch would ensure that any pointer returned from parsing functions is validated before use, preventing the null pointer dereference.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Target: ASUS AC68U router running firmware 3.0.0.4.384.82230.
• Network access to the router's HTTP/HTTPS management interface.
• No authentication required.

Exploitation Steps:

1. Identify the target router's IP address (e.g., 192.168.1.1).
2. Craft a malicious HTTP request that triggers the null pointer dereference. Since no public exploit exists, this requires reverse engineering the httpd binary to find the vulnerable code path.
3. Send the crafted packet using a tool like netcat, curl, or a custom Python script.

Example Python Script (Hypothetical):

import socket

target_ip = "192.168.1.1"
target_port = 80

# Craft a malformed HTTP request that triggers the vulnerability
# This is a placeholder; actual payload requires reverse engineering
payload = b"GET / HTTP/1.1\r\nHost: " + target_ip.encode() + b"\r\nX-Malformed: \x00\r\n\r\n"

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((target_ip, target_port))
sock.send(payload)
response = sock.recv(4096)
print(response)
sock.close()

Expected Outcome: The httpd process crashes, and subsequent HTTP requests to the router will fail (connection refused or timeout).

Blue Team (Detection & Defense)

Detection:

• Monitor for repeated HTTP requests with malformed headers or unusual patterns.
• Use network intrusion detection systems (NIDS) to flag packets that deviate from standard HTTP protocol.
• Enable logging on the router (if available) to capture crash events.

Defense:

• Restrict access to the router's web interface to trusted IP addresses only (e.g., via firewall rules).
• Disable remote management if not required.
• Apply any firmware updates from ASUS as soon as they become available.
• Use a VPN to access the management interface instead of exposing it directly.

Indicators of Compromise (IOCs)

Network IOCs:

• TCP packets to port 80/443 with malformed HTTP headers (e.g., null bytes, missing required fields).
• Repeated connection attempts followed by sudden termination (indicating service crash).
• HTTP responses with status codes 400 or 500 before the crash.

System IOCs:

• Router logs showing httpd process crash (e.g., segmentation fault).
• Unexpected restart of the httpd process.
• Inability to access the web management interface.

File IOCs:

• Core dump files (if enabled) in /tmp or /var on the router.

Detection Engineering

YARA Rule

rule CVE_2024_26342_ASUS_AC68U_DoS {
    meta:
        description = "Detects network packets targeting CVE-2024-26342 null pointer dereference in ASUS AC68U httpd"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-26342"
    strings:
        $http_get = "GET" ascii
        $http_host = "Host:" ascii
        $null_byte = {00}
    condition:
        $http_get at 0 and $http_host and #null_byte > 0
}

Sigma Rule

title: CVE-2024-26342 ASUS AC68U HTTP DoS Attempt
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects network packets with null bytes in HTTP headers targeting ASUS AC68U routers
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2024-26342
logsource:
    category: network
    product: suricata
detection:
    selection:
        - http.uri|contains: "\x00"
        - http.header_names|contains: "\x00"
        - http.header_values|contains: "\x00"
    condition: selection
falsepositives:
    - Legitimate traffic with unusual encoding (rare)
level: high

Suricata Rule

alert tcp $EXTERNAL_NET any -> $HOME_NET 80 (msg:"CVE-2024-26342 ASUS AC68U HTTP Null Pointer Dereference DoS Attempt"; flow:to_server,established; content:"|00|"; http_client_body; nocase; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Mitigation:

1. Restrict Access: Use firewall rules to limit access to the router's web interface to only trusted IP addresses.
2. Disable Remote Management: If not required, disable remote management from the WAN side.
3. Use VPN: Access the management interface only through a VPN tunnel.

Long-Term Remediation:

1. Firmware Update: Monitor ASUS's official support page for a firmware update that patches this vulnerability. Apply it as soon as it becomes available.
2. Replace Hardware: If the router is end-of-life and no patch is released, consider replacing it with a supported model.
3. Network Segmentation: Place the router in a separate network segment to limit exposure.

Workaround:

• If the web interface is not critical, consider disabling the HTTP service entirely and managing the router via SSH or Telnet (if enabled).

Valters IT