CVE-2026-94003

Executive Summary

CVE-2026-94003 is a critical stack-based buffer overflow (CWE-119) in the Comfast CF-N1-S firmware version 2.6.0.1, located in the get_css_path_from_uri function of the /cgi-bin/mbox-config web management endpoint. An unauthenticated remote attacker can trigger the overflow by sending a crafted HTTP request to the affected CGI handler, potentially achieving arbitrary code execution on the device. With a CVSS v3.1 score of 10.0 (AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H), this vulnerability represents a maximum-severity risk to any internet-exposed or network-reachable Comfast CF-N1-S device, and public exploit details are already circulating.

Technical Analysis

The vulnerability resides in the web management interface exposed by the Comfast CF-N1-S, specifically within the /cgi-bin/mbox-config CGI binary. According to the NVD description, the affected function is get_css_path_from_uri, which processes URI input and is vulnerable to a stack-based buffer overflow.

Stack-based buffer overflows occur when a program writes more data to a fixed-length buffer allocated on the call stack than the buffer can hold. In CGI-based embedded web interfaces, such as those commonly found in consumer and SMB networking gear, URI components (path, query strings, or headers) are frequently copied into fixed-size stack buffers using unsafe string routines (e.g., strcpy, sprintf, strcat) without bounds checking. When the input exceeds the buffer size, adjacent stack memory — including the saved return address and frame pointers — is overwritten, allowing the attacker to redirect program execution.

The CVSS vector indicates several aggravating factors:

• AV:N (Network) — exploitable over the network, remotely.
• AC:L (Low) — no special conditions or race windows required.
• PR:N (None) — no authentication required to reach the vulnerable function.
• UI:N (None) — no user interaction necessary.
• S:C (Changed) — a successful exploit impacts resources beyond the vulnerable component's own security scope, implying the attacker can pivot from the CGI context to broader system compromise.
• C:H/I:H/A:H — full loss of confidentiality, integrity, and availability.

Collectively, this indicates that an unauthenticated remote attacker who can reach /cgi-bin/mbox-config may overwrite the stack and gain arbitrary code execution, leading to full device compromise. Device firmware typically runs as root in embedded Linux/BusyBox environments, so code execution in the CGI process often translates to full control of the device.

The specific overflow primitive (return-address overwrite, function pointer corruption, etc.) and the exact input length required to overflow the buffer are not disclosed in the available NVD data. Likewise, no ASLR/NX/stack-canary information is available for this firmware. These specifics should be determined during authorized testing on owned hardware in a controlled lab.

The attack surface is the HTTP management interface. Any device with the web UI reachable — from the WAN, a LAN, or via port forwarding — is in scope.

Exploitation Scenarios

No public PoC is included in this dataset, but the NVD description states that the exploit "has been disclosed to the public and may be used." The following attack chain is inferred at the vulnerability-class level (stack-based buffer overflow in a CGI URI handler):

1. Reconnaissance / Target Identification The attacker scans for Comfast CF-N1-S devices using Shodan dorks (e.g., product:"Comfast CF-N1-S" or pages referencing the CF-N1-S management interface). Any host exposing the web management interface on its HTTP port is a candidate. Firmware version 2.6.0.1 is the confirmed affected version.

2. Triggering the Vulnerable Function The attacker issues a crafted HTTP request to /cgi-bin/mbox-config. The URI is processed by get_css_path_from_uri, which copies URI-derived data into a fixed-size stack buffer. An oversized, malformed URI component causes the buffer to overflow into adjacent stack memory.

3. Payload / Execution Method (class-level) Because this is a stack-based buffer overflow, the payload consists of a padding region to reach the saved return address (or another control-flow-relevant stack slot), followed by an attacker-chosen value that redirects execution to attacker-controlled code or ROP gadgets. No specific offsets, gadget addresses, or shellcode details are available in the provided data — these are device- and firmware-build-specific and must not be assumed.

4. Post-Exploitation Impact Successful exploitation yields code execution in the context of the CGI handler, which on embedded devices commonly runs with elevated (root) privileges. This enables:

   • Full read/write access to device configuration and credentials.
   • Persistent implant installation (e.g., adding a startup script).
   • Use of the device as a pivot point into the internal network.
   • Participation in botnets (common for consumer/SMB router class devices).

Note: No public PoC, Nuclei template, or exploit code is present in this dataset (PoC Status field is "Public" per NVD description, but no artifact is bundled here). All mechanics above are inferred from the vulnerability class and must be validated only on authorized, owned hardware.

Impact Assessment

With a CVSS v3.1 base score of 10.0, CVE-2026-94003 is at the maximum severity tier. The business and operational impact is severe:

• Confidentiality (High): Attackers can extract configuration data, Wi-Fi credentials, administrative passwords, and possibly VPN or device-identity material stored on the device.
• Integrity (High): Firmware, configuration, and routing/DNS settings can be modified, enabling redirection of traffic, DNS hijacking, or persistent backdoor insertion.
• Availability (High): A crash from the overflow can render the device unusable (DoS); successful RCE gives the attacker the ability to disrupt all network services.
• Scope (Changed): Impact extends beyond the vulnerable web component. A compromised gateway/router affects every host and user behind it, magnifying the blast radius significantly.

Affected Systems: Comfast CF-N1-S running firmware 2.6.0.1. Because this is a networking device, a single compromised unit can expose an entire downstream network. Any deployment where the management interface is reachable from untrusted networks (Internet, guest VLAN, shared LAN) is at immediate risk. Even LAN-only exposure is concerning given the unauthenticated nature of the flaw.

Blast Radius: Potentially every device on the same network segment as a compromised CF-N1-S, plus any networks routed through it. Supply-chain-style risk applies if these devices are shipped to customers in a default, exposed configuration.

Detection Guidance

Sigma Rule

title: Comfast CF-N1-S Stack Buffer Overflow Exploit Attempt (CVE-2026-94003)
id: 8f5c2d1a-9400-4cve-9b03-comfast0001
status: experimental
description: Detects HTTP requests targeting the vulnerable get_css_path_from_uri function via /cgi-bin/mbox-config with abnormally long URI query strings characteristic of a stack-based buffer overflow attempt against Comfast CF-N1-S firmware 2.6.0.1.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-94003
author: valtersit.com Threat Intelligence
date: 2026/01/01
logsource:
  category: webserver
  product: generic
detection:
  selection_uri:
    cs-uri-stem|contains: '/cgi-bin/mbox-config'
  selection_length:
    cs-uri-query|re: '.{512,}'
  condition: selection_uri and selection_length
fields:
  - c-ip
  - cs-uri-stem
  - cs-uri-query
  - sc-status
falsepositives:
  - Legitimate but unusually long query strings (rare)
  - Internal vulnerability scanners
level: critical
tags:
  - attack.t1190
  - cve.2026.94003

YARA Rule

rule CVE_2026_94003_Comfast_CF_N1_S_BufferOverflow
{
    meta:
        description = "Detects HTTP exploit attempts targeting the Comfast CF-N1-S get_css_path_from_uri stack buffer overflow (CVE-2026-94003)"
        author = "valtersit.com Threat Intelligence"
        date = "2026-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-94003"
        severity = "critical"

    strings:
        $uri_target = "/cgi-bin/mbox-config" ascii wide nocase
        $overflow_pattern = /\/cgi-bin\/mbox-config\?[A-Za-z0-9_\-\.=%]{512,}/

    condition:
        any of them
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-94003 Comfast CF-N1-S get_css_path_from_uri Stack Buffer Overflow Attempt"; flow:to_server,established; http.uri; content:"/cgi-bin/mbox-config"; http.uri; pcre:"/\/cgi-bin\/mbox-config\?[^\s]{512,}/i"; reference:cve,2026-94003; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-94003; classtype:attempted-admin; sid:9400310; rev:1;)

Elastic Detection

network where
    url.path : "/cgi-bin/mbox-config" and
    length(url.query) >= 512

Splunk SPL Query

index=web OR index=proxy
| eval uri=coalesce(uri, url, cs_uri_stem)
| eval query=coalesce(query_string, cs_uri_query)
| where like(uri, "%/cgi-bin/mbox-config%")
| eval qlen=len(query)
| where qlen >= 512
| stats count min(_time) as first_seen max(_time) as last_seen values(src_ip) as sources by uri, host
| sort - count

Wazuh OSSEC Rule

<group name="web,comfast,cve-2026-94003,">
  <rule id="940031" level="12">
    <if_sid>31100</if_sid>
    <id>^/cgi-bin/mbox-config</id>
    <regex>GET /cgi-bin/mbox-config\?.{512,}</regex>
    <description>CVE-2026-94003: Possible Comfast CF-N1-S stack buffer overflow attempt against /cgi-bin/mbox-config (get_css_path_from_uri)</description>
    <mitre>
      <id>T1190</id>
    </mitre>
    <group>cve_2026_94003,buffer_overflow,web_exploit,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source).

Because no vendor fix is available, risk reduction must rely on compensating controls and network architecture.

1. Immediate Mitigations

• Disable remote management. Turn off WAN-side HTTP/HTTPS management on all Comfast CF-N1-S devices.
• Network segmentation. Place the device management interface on an isolated management VLAN that is not reachable from untrusted networks.
• Restrict access by IP. If management must be enabled, restrict reachable source IPs to trusted admin workstations only.
• Block external scanning/indexing. Ensure the device's admin interface is not indexed by Shodan and that NAT/port-forwarding rules do not expose the web UI.
• Monitoring. Deploy the Suricata/Sigma/Wazuh detections above at the perimeter and on the LAN to catch exploitation attempts against /cgi-bin/mbox-config.

2. Patch / Upgrade Steps No patch, vendor advisory, or fixed version is documented in this dataset. Actions:

• Monitor the Comfast vendor support site and firmware download page for a CF-N1-S firmware release newer than 2.6.0.1.
• Register for vendor security notifications and check the NVD entry for CVE-2026-94003 for updated references.
• If the device is end-of-life or no patch is forthcoming, plan replacement with a supported model.

3. Long-Term Hardening

• Maintain an inventory of network devices and track firmware versions centrally.
• Enforce a policy against exposing management planes to the Internet.
• Adopt secure-by-design procurement: prefer vendors with a published PSIRT/CVE process and timely firmware patches.
• Implement egress filtering and monitoring to detect device compromise (unexpected outbound traffic, beaconing).
• Consider firmware integrity verification and device attestation where supported.
• Recheck the CVSS integrity: since this is a full-severity, unauthenticated RCE, treat it as an emergency remediation item once a patch is released.

References

• NVD — CVE-2026-94003: https://nvd.nist.gov/vuln/detail/CVE-2026-94003
• CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer — https://cwe.mitre.org/data/definitions/119.html
• MITRE ATT&CK T1190 — Exploit Public-Facing Application — https://attack.mitre.org/techniques/T1190/
• Comfast official support/firmware portal (monitor for an updated advisory) — vendor site
• CISA Known Exploited Vulnerabilities Catalog (not currently listed; verify status) — https://www.cisa.gov/known-exploited-vulnerabilities-catalog

Threat actor / in-the-wild note: No confirmed threat actor campaign or in-the-wild exploitation evidence is referenced in the provided data. However, the NVD description explicitly states the exploit "has been disclosed to the public and may be used." Internet-exposed Comfast CF-N1-S devices should be treated as actively at risk, and defenders should assume opportunistic exploitation is possible or ongoing.