CVE-2026-76008

Executive Summary

CVE-2026-76008 is a critical stack-based buffer overflow vulnerability affecting the Comfast CF-N1-S device, firmware version 2.6.0.1. The flaw exists in the get_para_from_uri function within the /cgi-bin/mbox-config endpoint, specifically during URI parameter parsing of the width and height arguments. An unauthenticated remote attacker can trigger the overflow, potentially achieving remote code execution with high privileges on the device, leading to full compromise of the affected hardware. Given the CVSS score of 10.0 and the fact that no patch is available, this vulnerability represents an urgent risk for any organization deploying Comfast CF-N1-S devices in their network.

Technical Analysis

The vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer), indicating a classic memory corruption issue. The flaw resides in the function get_para_from_uri which is called during processing of HTTP requests directed to the /cgi-bin/mbox-config endpoint of the device's web management interface.

The vulnerable code path handles URI parameters width and height. When an attacker supplies an overly long string for either of these parameters, the function copies the data into a stack-allocated buffer without adequate bounds checking. This results in a stack-based buffer overflow, where an attacker can overwrite adjacent memory on the call stack, including saved return addresses and stack frame metadata.

The component is identified as "URI Parameter Parsing," indicating that the issue occurs during the parsing and extraction of parameters from the request URI. The mbox-config CGI endpoint is likely responsible for managing device configuration settings related to mailbox or messaging services on the device.

The attack can be initiated remotely, requiring no authentication (PR:N) and no user interaction (UI:N). The attack complexity is low (AC:L), meaning no special conditions or race conditions are required to exploit the flaw. The vulnerability has a security impact score of 10.0 with a scope change (S:C), meaning the impact extends beyond the vulnerable component to affect the broader security posture of the device.

The stack-based nature of this overflow is significant because it allows direct manipulation of the execution flow. A successful exploit would typically involve overwriting the saved instruction pointer (EIP/RIP) with an address pointing to attacker-controlled shellcode or a ROP chain placed within the overflowed buffer or elsewhere in memory.

Insufficient technical detail is available regarding the exact buffer size, stack layout, or mitigation features (such as ASLR/DEP) in place on the device. However, embedded devices of this class often lack robust memory protection mechanisms, increasing the likelihood of successful exploitation.

Exploitation Scenarios

The attack chain for CVE-2026-76008 can be reconstructed based on the vulnerability class and available information:

Step 1: Reconnaissance/Target Identification An attacker would first identify Comfast CF-N1-S devices exposed to the internet or internal networks. This can be accomplished via Shodan or similar scanning tools using device-specific fingerprints. The device's web management interface, likely on port 80 or 443, would be the primary target. The attacker would confirm the firmware version (2.6.0.1) by accessing the device's status or login page.

Step 2: Flaw Trigger Mechanism The attacker sends an HTTP request to the /cgi-bin/mbox-config endpoint with one or both of the width and height parameters containing an abnormally long string. For example, a GET request like GET /cgi-bin/mbox-config?width=<long_string>&height=<normal_value> HTTP/1.1 would initiate the vulnerable code path. The get_para_from_uri function processes the URI, extracts the width parameter, and attempts to copy it into a fixed-size stack buffer without proper bounds validation.

Step 3: Payload/Execution Method At the vulnerability-class level, the attacker would craft the overflow payload to overwrite the saved return address on the stack, redirecting execution to attacker-controlled code. On embedded Linux devices (which this likely is), the payload could be a standard ARM/MIPS shellcode that spawns a reverse shell or binds to a port. Alternatively, the attacker could use return-oriented programming (ROP) to call system functions. The exact payload structure depends on the device's architecture (ARM, MIPS, etc.), which is not specified in the available data.

Step 4: Post-Exploitation Impact Successful exploitation grants the attacker arbitrary code execution on the device with the privileges of the CGI process (likely root or a privileged user). This allows the attacker to:

• Extract configuration files, credentials, and network information
• Modify device settings, including routing and firewall rules
• Use the device as a pivot point into the internal network
• Install persistent backdoors or malware
• Leverage the device in botnets or as a launching pad for further attacks
• Disable the device, causing denial of service

No public PoC is available for this vulnerability; the attack chain described above is inferred from the vulnerability class and available technical details.

Impact Assessment

The CVSS v3.1 score of 10.0 places this vulnerability in the critical severity range. The vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H highlights the following:

• Attack Vector — Network: Remotely exploitable, no physical access required
• Attack Complexity — Low: No special conditions or race conditions needed
• Privileges Required — None: Unauthenticated exploitation
• User Interaction — None: No victim interaction needed
• Scope — Changed: Impact extends beyond the vulnerable component, affecting the device's overall security
• Confidentiality/Integrity/Availability — High: Full compromise of all three security properties

Business Impact: Comfast CF-N1-S devices are typically used as network infrastructure components (likely router or access point hardware based on Comfast's product line). A successful exploit gives attackers full control of the network device, enabling:

• Lateral movement into the internal network
• Data exfiltration of network traffic
• Network disruption and denial of service
• Persistent backdoor access for future operations
• Potential customer data exposure if the device handles sensitive traffic

Affected Systems: While the NVD description specifically identifies Comfast CF-N1-S firmware 2.6.0.1, other Comfast devices sharing the same firmware base or similar code could also be affected. The lack of vendor patch information suggests that the entire product line could remain vulnerable.

Blast Radius: Because this is a network-facing device vulnerability with no authentication required, the blast radius includes any organization deploying these devices on their perimeter or in environments accessible by untrusted networks. The scope change (S:C) indicates that a successful compromise of the device can affect other components beyond the device itself, such as the network segments it bridges.

EPSS: Not yet scored by FIRST.org; no exploit probability data available at this time.

Detection Guidance

The following detection rules target the request patterns associated with CVE-2026-76008 exploitation attempts. Note that these rules are based on the vulnerability characteristics and should be tested against legitimate traffic to minimize false positives.

Sigma Rule

title: Comfast CF-N1-S Buffer Overflow Exploit Attempt
id: a3c5f8e2-9d4b-4e2f-b7a1-6c3d9e5f2b8a
status: experimental
description: Detects attempts to exploit stack buffer overflow in Comfast CF-N1-S mbox-config endpoint via width/height parameters
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2026-76008
tags:
    - attack.initial-access
    - attack.t1190
    - cve.2026-76008
    - cwe.119
logsource:
    category: webserver
    product: generic
detection:
    selection:
        cs-method:
            - GET
        cs-uri-query|contains:
            - '/cgi-bin/mbox-config'
            - 'mbox-config'
        cs-uri-query|re:
            - '(width|height)=.{500,}'
            - '(width|height)=[A-Za-z0-9%]{200,}'
    condition: selection
falsepositives:
    - Legitimate long parameter values (unlikely with normal usage)
    - Very large configuration requests
level: critical

YARA Rule

rule comfast_mbox_config_overflow
{
    meta:
        author = "ValtersIT SOC"
        description = "Detect string patterns associated with CVE-2026-76008 exploitation attempts"
        cve = "CVE-2026-76008"
        date = "2026-01-15"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-76008"
    strings:
        $uri1 = "/cgi-bin/mbox-config" ascii nocase
        $uri2 = "mbox-config" ascii nocase
        $param1 = "width=" ascii nocase
        $param2 = "height=" ascii nocase
        $long_pattern = /(width|height)=[^\s&]{200,}/ nocase
        $overflow_pattern = /(width|height)=(A{200,}|B{200,}|C{200,}|%41{200,})/ nocase
    condition:
        any of ($uri*) and any of ($param*) and any of ($long_pattern * 1)
}

Suricata IDS Rule

alert http any any -> $HOME_NET any (
    msg:"ET EXPLOIT Comfast CF-N1-S mbox-config stack buffer overflow attempt";
    flow:to_server,established;
    content:"/cgi-bin/mbox-config"; http_uri;
    pcre:"/(width|height)=[^\s&]{200,}/Ui";
    classtype:attempted-admin;
    sid:202676008;
    rev:1;
    reference:cve,2026-76008;
    metadata:created_at 2026_01_15, updated_at 2026_01_15;
    priority:1;
)

Elastic Detection

sequence with maxspan=1s
  [ network where event.category == "network_traffic" and
    destination.port == 80 and
    network.protocol == "http" and
    url.path == "/cgi-bin/mbox-config" and
    url.query: "*(width|height)=*{200,}" ]

Splunk SPL Query

index=web sourcetype=access_combined OR sourcetype=iis
| where LIKE(uri_path, "%/cgi-bin/mbox-config%")
| rex field=uri_query "(?<param_name>width|height)=(?<param_value>[^\s&]+)"
| where len(param_value) > 200
| stats count by src_ip, uri_path, param_name, len(param_value), _time
| sort -_time

Wazuh OSSEC Rule

<group name="webserver,">
  <rule id="150779" level="15">
    <if_sid>31100</if_sid>
    <match>mbox-config</match>
    <regex>(width|height)=[^ \t\r\n]{200,}</regex>
    <description>Possible CVE-2026-76008 exploitation attempt against Comfast CF-N1-S device</description>
    <group>cve-2026-76008,</group>
    <mitre>
      <id>T1190</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch Confidence: 0/4 — UNPATCHED — no patch evidence from any tracked source.

As of this report, no vendor patch is available for CVE-2026-76008. The Comfast CF-N1-S device firmware 2.6.0.1 remains vulnerable. The following steps should be prioritized:

1) Immediate Mitigations

• Network Access Restriction: Block external access to the web management interface (default ports 80/443) of the affected devices. Restrict access to trusted administrative networks only using firewall rules or ACLs.
• DDoS Protection/Brute-Force Mitigation: Enable WAF or IPS rules that flag requests to /cgi-bin/mbox-config with abnormally long parameter values.
• Firmware Review: Check the Comfast website or contact vendor support for any beta or re-release firmware versions that may address this issue.
• Vulnerability Scanning: Run vulnerability scans to identify all CF-N1-S devices on the network using this firmware version.
• Monitor Logs: Review device access logs for unusual requests to the mbox-config endpoint with large parameter values.

2) Patch/Upgrade Steps

• Contact the vendor (Comfast) directly to inquire about an available security update or firmware revision.
• If the device is near end-of-life, plan for hardware replacement with a vetted alternative that has active security support.
• Upon vendor patch release, follow proper firmware upgrade procedures: backup configuration, verify checksum, stage upgrade, and test in a non-production environment first.

3) Long-Term Hardening

• Network Segmentation: Place management interfaces of embedded devices on isolated management VLANs with strict access controls.
• Least Privilege: Ensure devices are not accessible from untrusted networks; allow only necessary traffic through perimeter firewalls.
• Monitoring: Implement detection rules outlined above in your SIEM/SOC stack to alert on exploitation attempts.
• Asset Inventory: Maintain accurate records of all embedded devices, firmware versions, and support status.
• Vendor Management: Establish a security contact process with the vendor for future vulnerability notifications.
• Replace Vulnerable Hardware: Given the critical nature (CVSS 10.0) and lack of patch, strongly consider hardware replacement as the most reliable risk mitigation strategy.

References

1. NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2026-76008
2. MITRE CWE-119: https://cwe.mitre.org/data/definitions/119.html
3. Comfast Official Website: https://www.comfast.com (product support page — check for advisory)
4. ATT&CK T1190: https://attack.mitre.org/techniques/T1190/
5. FIRST CVSS Calculator: https://www.first.org/cvss/calculator/3.1#CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H

Threat Actor Activity: As of the writing of this report, there are no known threat actor campaigns exploiting CVE-2026-76008 in the wild. The vulnerability is not on the CISA KEV list. However, the unpatched status, ease of exploitation (no authentication required), and critical severity make this an attractive target for both opportunistic malware campaigns and targeted attacks against embedded network infrastructure. Network defenders should treat any observed exploitation attempts with high severity and respond promptly.