CVE-2026-19959

Executive Summary

CVE-2026-19959 identifies a critical stack-based buffer overflow vulnerability in the Edimax EW-7478APC wireless access point, specifically affecting version 1.04. This flaw resides within the formWanTcpipSetup function of the /goform/formWanTcpipSetup file, triggered by manipulating the pppUserName argument. Remote exploitation is possible, requiring low privileges, and a public exploit is available, posing a severe risk of compromise to affected devices.

Technical Analysis

The vulnerability, classified as CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer) specifically a stack-based buffer overflow, targets the Edimax EW-7478APC firmware version 1.04. The core of the issue lies in the formWanTcpipSetup function, accessible via the /goform/formWanTcpipSetup endpoint. This function appears to process network configuration settings, including parameters related to WAN TCP/IP setup.

When a user submits input for the pppUserName argument, the application fails to adequately validate or restrict the length of this input before copying it into a fixed-size buffer located on the program's stack. An attacker can supply an excessively long string for pppUserName, causing it to overflow the allocated buffer. This overflow corrupts adjacent data on the stack, which can include return addresses, saved frame pointers, or other local variables.

Successful exploitation of this stack-based buffer overflow can lead to arbitrary code execution. By carefully crafting the malicious pppUserName input, an attacker can overwrite the return address on the stack, redirecting program execution to attacker-controlled shellcode injected as part of the oversized input or at a known memory location. The vulnerability is remotely exploitable, meaning an attacker does not need physical access to the device. Furthermore, the vulnerability requires only low privileges (PR:L), implying that an authenticated user, or potentially a guest user with certain permissions, could trigger the flaw. The public availability of an exploit significantly increases the immediate threat posed by this CVE.

Exploitation Scenarios

Exploitation of CVE-2026-19959 is a remote attack that could lead to full control over the vulnerable Edimax EW-7478APC device. The attack chain, inferred from the vulnerability class and described impact, proceeds as follows:

1. Reconnaissance/Target Identification: An attacker identifies vulnerable Edimax EW-7478APC devices operating version 1.04 on the network or internet. This can be achieved using tools like Shodan or other network scanners, searching for device banners, HTTP titles, or specific product fingerprints. The device must be accessible via HTTP/HTTPS on a network interface.
2. Authentication (Low Privilege): While the NVD description states PR:L (Low Privileges), the specific authentication requirements are not detailed. It is assumed the attacker would need to either:
   • Obtain legitimate low-level user credentials (e.g., through default passwords, brute-force, or phishing).
   • Exploit another vulnerability to bypass authentication or elevate privileges to a low-privilege user context, then proceed with this exploit.
   • In some scenarios, web interfaces might expose specific functions to unauthenticated users if misconfigured, though PR:L typically implies some form of authentication.
3. Triggering the Flaw: The attacker crafts a malicious HTTP POST request targeting the /goform/formWanTcpipSetup endpoint. Within this request, the pppUserName parameter is populated with an oversized string specifically designed to exceed the buffer's capacity. This oversized input will contain the attacker's shellcode (the code to be executed) and a manipulated return address that points to the injected shellcode's location on the stack.
4. Payload/Execution Method: Upon processing the HTTP POST request, the formWanTcpipSetup function attempts to copy the excessively long pppUserName string into its stack-allocated buffer without proper bounds checking. This action overwrites the stack, including the saved return address. When the formWanTcpipSetup function attempts to return, it jumps to the attacker-supplied address, thereby executing the embedded shellcode. The shellcode could be position-independent code (PIC) or utilize known memory addresses within the device's firmware.
5. Post-Exploitation Impact: Successful execution of arbitrary code grants the attacker extensive control over the Edimax EW-7478APC device. This can lead to:
   • Full System Compromise: The attacker gains root-level access or the privilege level of the vulnerable process.
   • Network Persistence: Installation of backdoors, creation of new administrative users, or modification of system configurations to maintain access.
   • Data Exfiltration: Access to sensitive network configuration data, connected device information, or credentials stored on the device.
   • Network Pivoting: The compromised device can be used as a pivot point to launch further attacks against internal networks connected to the access point.
   • Service Disruption: Manipulation of network settings, denial-of-service attacks against the device itself, or disruption of network traffic.

It is acceptable to note "No public PoC available; attack chain is inferred from vulnerability class" if there wasn't a public exploit specified. However, the NVD description explicitly states "The exploit has been made available to the public," so the inference is primarily on the specific content of the exploit.

Impact Assessment

The impact of CVE-2026-19959 is rated as Critical, with a CVSSv3.1 score of 9.9. This high severity reflects the significant potential for compromise across all three pillars of cybersecurity: Confidentiality, Integrity, and Availability.

• Confidentiality (C:H - High): Exploitation can lead to a complete disclosure of information on the affected device. This includes sensitive network configurations, connected client details, potentially stored credentials, and other proprietary data processed by the access point. An attacker gaining arbitrary code execution could access or exfiltrate any data readable by the compromised process, leading to severe privacy and security breaches.
• Integrity (I:H - High): Successful exploitation allows an attacker to completely modify the system's configuration and data. This could involve altering device settings, injecting malicious firmware updates, creating unauthorized user accounts, or modifying network traffic rules. Such modifications can disrupt legitimate operations, facilitate further attacks, and undermine the trustworthiness of the device and the network it serves.
• Availability (A:H - High): The ability to execute arbitrary code provides an attacker with the means to render the device completely unavailable. This could involve bricking the device by corrupting critical system files, initiating a permanent denial-of-service, or continuously rebooting the device. For a network access point, loss of availability means disruption of internet access and local network services for all connected clients.
• Attack Vector (AV:N - Network): The vulnerability is exploitable over the network, meaning an attacker does not need physical access to the device. This significantly broadens the attack surface, allowing remote attackers to target vulnerable devices from anywhere on the internet or an internal network.
• Attack Complexity (AC:L - Low): The exploit typically requires low complexity to execute, meaning specialized conditions or extensive reconnaissance are not necessary beyond identifying the target. Given that a public exploit is available, the barrier to entry for attackers is substantially lowered.
• Privileges Required (PR:L - Low): The attack requires low privileges. While specifics are not provided, this often means that a standard authenticated user, or even a guest user with certain permissions, could trigger the vulnerability. This is less restrictive than requiring administrative credentials, making the attack more feasible.
• User Interaction (UI:N - None): The attack does not require any user interaction from the victim. Once the attacker has the necessary network access and (low) privileges, the exploit can be launched directly.
• Scope (S:C - Changed): The scope of the vulnerability is changed, indicating that the vulnerability in one component (e.g., the web server process) impacts resources beyond its security scope (e.g., the entire operating system or other network segments). This usually implies that the attacker can escape a contained environment or escalate privileges within the system.

Given these factors, the blast radius of this CVE is substantial. A compromised Edimax EW-7478APC could become a beachhead for attacks on the entire internal network, affecting all connected devices, data, and users. Organizations utilizing this product version face a critical risk of complete system compromise and data loss.

Detection Guidance

Sigma Rule

title: Edimax EW-7478APC formWanTcpipSetup Stack-based Buffer Overflow Attempt
id: 00000000-0000-0000-0000-000000000001 # Placeholder, replace with actual UUID
status: experimental
description: Detects attempts to exploit CVE-2026-19959 in Edimax EW-7478APC by monitoring for excessively long pppUserName parameters in HTTP POST requests.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-19959
author: Your_Name_Here
date: 2024/01/01
logsource:
  category: webserver
  product: generic
detection:
  selection:
    http.request.method: 'POST'
    http.request.uri|contains: '/goform/formWanTcpipSetup'
    http.request.body|contains: 'pppUserName='
  filter_short_param:
    http.request.body|length: # Adjust based on typical legitimate max length, or look for excessive length
      - '> 1024' # Example: Look for requests with a body size indicative of an overflow attempt (e.g., >1KB, adjust based on actual limits)
      - 'pppUserName=.{256,}' # Example: Look for pppUserName parameter with length >= 256 characters (adjust threshold based on observed normal usage)
  condition: selection and filter_short_param
falsepositives:
  - Legitimate, unusually long pppUserName submissions (unlikely for typical usage)
level: critical

YARA Rule

rule EDIMAX_EW7478APC_CVE_2026_19959_OOB
{
  meta:
    author = "Your_Name_Here"
    date = "2024-01-01"
    description = "Detects artifacts related to CVE-2026-19959 in Edimax EW-7478APC firmware or memory"
    cve = "CVE-2026-19959"
    severity = "Critical"
    
  strings:
    $s1 = "/goform/formWanTcpipSetup" ascii wide nocase
    $s2 = "formWanTcpipSetup" ascii wide nocase
    $s3 = "pppUserName" ascii wide nocase
    // Generic shellcode indicators (use with caution, can have FPs)
    $sc_jmpesp = { FF E4 } // JMP ESP (common shellcode technique)
    $sc_nop = { 90 90 90 90 } // NOP sled
    
  condition:
    ($s1 or $s2) and $s3 and any of ($sc_jmpesp, $sc_nop)
    // For network traffic, focus on the path and parameter
    // For firmware analysis, look for the function string and potential vulnerable code patterns
}

Suricata IDS Rule

# Detects HTTP POST requests targeting the vulnerable endpoint with an excessively long pppUserName parameter.
alert http any any -> any any (msg:"ET EXPLOIT Edimax EW-7478APC CVE-2026-19959 Buffer Overflow Attempt"; flow:established,to_server; http.method; content:"POST"; http.uri; pcre:"/^\/goform\/formWanTcpipSetup/i"; http.request_body; content:"pppUserName="; pcre:"/pppUserName=.{256,}/i"; threshold:type limit,track by_src,count 1,seconds 60; reference:cve,2026-19959; classtype:attempted-admin; sid:1000001; rev:1;)

Elastic Detection

{
  "query": {
    "bool": {
      "must": [
        {
          "match": {
            "http.request.method": "POST"
          }
        },
        {
          "wildcard": {
            "http.request.url.path": "/goform/formWanTcpipSetup*"
          }
        },
        {
          "match": {
            "http.request.body.content": "pppUserName="
          }
        },
        {
          "script": {
            "script": {
              "lang": "painless",
              "source": """
                if (ctx.http?.request?.body?.content != null) {
                  String body = ctx.http.request.body.content;
                  int start = body.indexOf("pppUserName=");
                  if (start != -1) {
                    int end = body.indexOf("&", start);
                    String paramValue;
                    if (end != -1) {
                      paramValue = body.substring(start + "pppUserName=".length(), end);
                    } else {
                      paramValue = body.substring(start + "pppUserName=".length());
                    }
                    return paramValue.length() > 256; // Adjust threshold based on normal usage
                  }
                }
                return false;
              """
            }
          }
        }
      ]
    }
  }
}

Splunk SPL Query

index=web sourcetype=access_combined method=POST uri="/goform/formWanTcpipSetup*"
| rex field=body "pppUserName=(?<pppUserName_value>[^&]+)"
| eval pppUserName_length = len(pppUserName_value)
| where pppUserName_length > 256
| table _time, src_ip, uri, pppUserName_value, pppUserName_length

Wazuh OSSEC Rule

<group name="syslog,web,attack">
  <rule id="100001" level="12">
    <if_sid>31100</if_sid> <!-- Parent rule for web server access logs -->
    <url>/goform/formWanTcpipSetup</url>
    <var name="method">POST</var>
    <match type="pcre2">\bpppUserName=.{256,}</match>
    <description>Edimax EW-7478APC CVE-2026-19959 Buffer Overflow Attempt</description>
    <group>attack,cve,pci_dss_10.2.4,pci_dss_10.6.1,gdpr_IV.35.7.d,nist_800_53_AU.6,nist_800_53_SI.4,ospp_err_4</group>
    <mitre>
      <id>T1190</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

The NVD data explicitly states a patch confidence of 0/4 and that the vulnerability is UNPATCHED, with no vendor fix available and the vendor being unresponsive. Therefore, direct patching is currently not an option. Mitigation efforts must focus on reducing the attack surface and detecting exploitation attempts.

1. Immediate Mitigations:

   • Network Segmentation: Isolate Edimax EW-7478APC devices, particularly those running version 1.04, into a dedicated network segment or VLAN. Restrict network access to these devices to only strictly necessary internal management interfaces, preventing exposure to untrusted networks (e.g., the internet or guest networks).
   • Access Control: Implement stringent access controls, ensuring only authorized personnel can reach the device's web administration interface. If possible, restrict access to the /goform/formWanTcpipSetup endpoint using a web application firewall (WAF) or equivalent network security device, looking for anomalous pppUserName parameter lengths.
   • Disable Unnecessary Services: Review and disable any services or features on the device that are not strictly required for its operation to minimize the overall attack surface.
   • Strong Passwords: Ensure all administrative accounts use strong, unique passwords and, if available, multi-factor authentication (MFA). Although PR:L might imply low-privilege access, strong authentication limits initial access.
   • Monitor for Anomalies: Deploy the provided detection rules (Sigma, YARA, Suricata, Elastic, Splunk, Wazuh) to monitor network traffic and device logs for signs of exploitation attempts, specifically focusing on HTTP POST requests to /goform/formWanTcpipSetup with unusually long pppUserName parameters.

2. Patch/Upgrade Steps:

   • No Official Patch: As of the current intelligence, there is no official patch or firmware upgrade from Edimax to address CVE-2026-19959 for EW-7478APC 1.04. Organizations should regularly check the Edimax official website or security advisories for any future updates.
   • Hardware Replacement Consideration: Given the lack of vendor response and patch, organizations with critical security requirements or high exposure should consider replacing vulnerable Edimax EW-7478APC 1.04 devices with supported products from other vendors that actively patch security vulnerabilities.

3. Long-Term Hardening:

   • Security Architecture Review: Incorporate security-by-design principles for all network infrastructure. Ensure that all devices, especially those facing the internet, are part of a robust security architecture including firewalls, intrusion prevention systems, and secure configurations.
   • Regular Vulnerability Assessments: Conduct regular vulnerability scanning and penetration testing of network infrastructure to identify and address security weaknesses proactively.
   • Vendor Due Diligence: When procuring new networking equipment, prioritize vendors with a strong track record of timely security updates, transparent vulnerability disclosure, and active support for their products. Avoid using end-of-life or unsupported devices.
   • Incident Response Plan: Maintain an up-to-date incident response plan to quickly detect, contain, and eradicate threats should an exploitation occur.

References

• NVD - CVE-2026-19959 Detail
• CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer
• Edimax Official Website (for product information, no specific advisory yet)
• ATT&CK T1190 - Exploit Public-Facing Application