CVE-2024-27568

Executive Summary

CVE-2024-27568 is a critical stack-based buffer overflow vulnerability discovered in LBT T300 and T390 routers running firmware version v2.2.1.8. The flaw resides in the setupEC20Apn function, specifically within the handling of the apn_name_3g parameter. An unauthenticated attacker can trigger a Denial of Service (DoS) by sending a crafted POST request, causing the device to crash or become unresponsive. No patch is currently available from the vendor, and no public exploit code has been released. The vulnerability is classified under CWE-121 (Stack-based Buffer Overflow) and aligns with MITRE ATT&CK tactic T1499 (Endpoint Denial of Service).

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, indicating insufficient data for a full vector calculation. However, based on the vulnerability characteristics, a reasonable assessment is:

• Attack Vector (AV): Network (N) – The exploit is sent over the network.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): None (N) – No user action required.
• Scope (S): Unchanged (U) – The exploit affects only the vulnerable component.
• Confidentiality (C): None (N) – No data exposure.
• Integrity (I): None (N) – No data modification.
• Availability (A): High (H) – Complete loss of availability.

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

Threat Level: High (7.5) – Unauthenticated remote DoS with no patch available.

Deep Dive & Mechanics

The vulnerability is a classic stack-based buffer overflow in the setupEC20Apn function of the LBT T300/T390 firmware. The function processes the apn_name_3g parameter from a POST request without proper bounds checking. When an attacker supplies an overly long string for this parameter, it overflows the stack buffer, overwriting the return address and other critical data. This leads to a crash (DoS) and potentially arbitrary code execution if the attacker can control the overwritten data.

Root Cause: Lack of input validation and unsafe use of functions like strcpy or sprintf that do not limit the length of copied data.

Attack Vector: The attacker sends a POST request to the vulnerable endpoint (likely /cgi-bin/setupEC20Apn or similar) with a maliciously long apn_name_3g value.

Impact: Immediate device crash, requiring a physical reboot. In a worst-case scenario, an attacker could achieve remote code execution (RCE) with root privileges, though no public exploit confirms this.

Vulnerable vs. Patched Code

No patched version is available. The vulnerable code snippet (hypothetical based on CWE-121) is:

// Vulnerable code in setupEC20Apn function
void setupEC20Apn(struct request *req) {
    char apn_name[64];
    char *apn_value = get_param(req, "apn_name_3g");
    strcpy(apn_name, apn_value); // No bounds check
    // ... rest of function
}

A patched version would use safe functions:

// Patched code
void setupEC20Apn(struct request *req) {
    char apn_name[64];
    char *apn_value = get_param(req, "apn_name_3g");
    strncpy(apn_name, apn_value, sizeof(apn_name) - 1);
    apn_name[sizeof(apn_name) - 1] = '\0';
    // ... rest of function
}

Exploitation & Lab Setup

Red Team

Lab Setup:

1. Obtain an LBT T300 or T390 router with firmware v2.2.1.8.
2. Connect the router to a test network (isolated from production).
3. Identify the router's IP address (e.g., 192.168.1.1).

Exploitation Steps:

1. Craft a POST request with a long apn_name_3g parameter:

   curl -X POST http://192.168.1.1/cgi-bin/setupEC20Apn \
   -d "apn_name_3g=$(python3 -c 'print("A"*1000)')"
   

2. Observe the router crash (loss of connectivity, no response to pings).
3. For potential RCE, use a pattern to overwrite the return address (requires reverse engineering).

Note: No public exploit code is available. The above is a proof-of-concept for DoS only.

Blue Team

Detection:

• Monitor for POST requests to /cgi-bin/setupEC20Apn with abnormally long apn_name_3g values.
• Use network intrusion detection systems (NIDS) to flag requests with payloads exceeding 64 bytes for this parameter.

Mitigation:

• Isolate affected devices on a separate VLAN.
• Implement web application firewall (WAF) rules to block oversized parameters.
• Monitor device logs for crashes or unexpected reboots.

Indicators of Compromise (IOCs)

• Network:
  • POST requests to /cgi-bin/setupEC20Apn with apn_name_3g > 64 bytes.
  • Source IPs repeatedly sending such requests.
• Host:
  • Router logs showing segmentation faults or kernel panics.
  • Unexpected device reboots.
• File:
  • No file-based IOCs as the exploit is memory-based.

Detection Engineering

YARA Rule

rule CVE_2024_27568_LBT_StackOverflow {
    meta:
        description = "Detects exploit attempts for CVE-2024-27568 targeting LBT routers"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2024-27568"
    strings:
        $payload = "apn_name_3g=" ascii wide nocase
        $long_string = /apn_name_3g=[A-Za-z0-9]{100,}/ ascii
    condition:
        $payload and #long_string > 0
}

Sigma Rule

title: CVE-2024-27568 LBT Router Stack Overflow Attempt
id: 8a3f7c2e-5d1b-4a9f-8c6e-2b1d3f4a5c6d
status: experimental
description: Detects HTTP POST requests with long apn_name_3g parameter targeting LBT routers
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: '/cgi-bin/setupEC20Apn'
        cs-uri-query|re: 'apn_name_3g=.{100,}'
    condition: selection
falsepositives:
    - Legitimate long APN names (unlikely)
level: high

Suricata Rule

alert http any any -> $HOME_NET any (
    msg:"CVE-2024-27568 LBT Router Stack Overflow Attempt";
    flow:to_server,established;
    content:"POST";
    http_method;
    content:"/cgi-bin/setupEC20Apn";
    http_uri;
    content:"apn_name_3g=";
    http_client_body;
    pcre:"/apn_name_3g=.{100,}/Ri";
    classtype:attempted-dos;
    sid:1000001;
    rev:1;
    reference:cve,2024-27568;
)

Remediation & Mitigation

Immediate Actions:

1. Isolate affected devices: Place LBT T300/T390 routers on a separate VLAN with restricted access.
2. Monitor for exploitation: Deploy the provided detection rules.
3. Contact vendor: Request a firmware patch from LBT.

Long-term Solutions:

• Replace affected routers with patched or alternative hardware.
• Implement network segmentation to limit exposure of IoT devices.
• Apply virtual patching via WAF or NIDS.

Workarounds:

• Disable the vulnerable endpoint if possible (e.g., block /cgi-bin/setupEC20Apn via firewall).
• Restrict administrative access to trusted IPs only.

Valters IT