CVE-2026-77022

Executive Summary

CVE-2026-77022 is a critical stack-based buffer overflow vulnerability (CVSS 9.9) in the Comfast CF-N1-S wireless access point, firmware version 2.6.0.1, specifically within the SSID Configuration component. An authenticated or low-privileged remote attacker can trigger the overflow by sending a crafted ssid argument to the ptest_ssid section of the /cgi-bin/mbox-config endpoint, achieving memory corruption that can lead to remote code execution with the privileges of the web service. The vulnerability is confirmed unpatched at the time of this writing, and a public exploit has already been released, making this a high-priority exposure for any organization deploying Comfast CF-N1-S devices on their network perimeter. Successful exploitation results in full compromise of the device (high confidentiality, integrity, and availability impact), and given the network adjacency (AV:N) and scope change (S:C), a single exploit can pivot from the device to the internal network.

Technical Analysis

Vulnerability Mechanism & Class

The flaw falls under CWE-119 — Improper Restriction of Operations within the Bounds of a Memory Buffer. The NVD description identifies a stack-based buffer overflow triggered inside the function sub_44B438 of the file /cgi-bin/mbox-config. This is a classic stack overflow where a fixed-size stack buffer receives user-supplied input (the ssid parameter) without sufficient length validation or boundary checking. When an attacker supplies a string longer than the allocated stack buffer, adjacent memory (saved frame pointer, return address, and local variables) is overwritten.

Technical specifics derived from the description:

• Function: sub_44B438 — internal symbol for the handler routine.
• Endpoint: /cgi-bin/mbox-config?method=SET&section=ptest_ssid.
• Parameter: ssid — the wireless network name string supplied by the caller.
• Attack vector: Remote — the CGI endpoint is exposed via the HTTP management interface.
• Privilege requirement: PR:L — some level of authenticated access or low-privileged session is required to reach the CGI handler.

Importantly, the NVD description does not specify the exact size limit of the vulnerable buffer, nor whether the overflow character encoding is ASCII/UTF-8 or binary-safe. Insufficient technical detail is available to state the precise overwrite offset or return-address distance within the stack frame. What is confirmed is that an oversized ssid value will overwrite the stack, and because the function is called in the context of a CGI process, the overwritten return address can be hijacked to redirect execution into attacker-controlled memory regions (either on the stack itself or in a NOP-sled + shellcode pattern).

Attack Surface

The attack surface is the device's web management interface, listening on the default HTTP port (commonly 80 or 8080 for these small-office access points). The CGI executable handling mbox-config is both the parser and the vulnerable program; there is no intermediary service that validates input length, and the ssid argument is passed straight through to the vulnerable stack frame. Because the device is likely deployed on the network edge (e.g., SOHO routers, retail branch locations), the management interface may be exposed to the internet either directly or via port-forwarding, widening the remotely exploitable surface.

Known exploitation status: The NVD description explicitly states "The exploit has been released to the public and may be used for attacks." This raises the probability of in-the-wild attempts, though no specific threat-actor attribution or campaign information is available in the source data.

Exploitation Scenarios

The attack chain below is derived strictly from the NVD description and the CWE-119 vulnerability class. No PoC specifics are available; the flow described is mechanism-level, not code-level.

Step 1 — Reconnaissance / Target Identification

An attacker identifies Comfast CF-N1-S devices by scanning for the HTTP management interface. Since the device has a distinctive default login banner and a web server fingerprint, Shodan-style searches (e.g., searching for the device's HTTP title or the mbox-config path in server logs) yield candidate targets. The attacker then verifies the firmware version (2.6.0.1) either by fetching the /cgi-bin/luci version page or by probing the management interface's response headers — though the exact probing method depends on the device's default behavior, which is not specified in the source data.

Step 2 — Triggering the Flaw

The attacker authenticates with low-privileged credentials (default credentials on many Comfast devices, or credentials gained through phishing/credential stuffing), or in some firmware variants the ptest_ssid section may be accessible without authentication if the device exposes the CGI endpoint unauthenticated (the NVD vector PR:L indicates low privilege is required, but this could include "guest" access). The attacker crafts an HTTP GET request to:

/cgi-bin/mbox-config?method=SET&section=ptest_ssid&ssid=<overflow_payload>

The ssid parameter is a plain-text string; the overflow occurs because the CGI handler sub_44B438 copies this string into a fixed-size stack buffer via an unsafe copy routine (e.g., strcpy or sprintf-style call — exact function name not disclosed in the description).

Step 3 — Payload / Execution Method

At the vulnerability-class level, the attacker supplies an oversized ssid value that exceeds the stack buffer size. The payload is structured to:

1. Fill the buffer with a padding pattern.
2. Overwrite the saved base pointer and return address with a controlled value pointing to attacker-controlled memory (often the stack itself).
3. Optionally include a NOP sled and shellcode, or ROP-chain gadgets, to execute arbitrary code on the device.

Because the device is a small embedded system (likely MIPS or ARM architecture), the shellcode is architecture-specific. The attacker either reuses a public exploit (which the NVD confirms exists) or adapts a generic MIPS/ARM bind-shell or reverse-shell payload.

Step 4 — Post-Exploitation Impact

Once code execution is achieved, the attacker runs with the privileges of the web server user (often root on embedded devices). From this foothold, the attacker can:

• Read and modify the device configuration (change SSID, admin credentials, or disable security controls).
• Install a persistent implant on the device's flash filesystem.
• Use the device as a pivot point into the internal LAN (scope change S:C — high impact).
• Leverage the device's network position to perform lateral attacks against other hosts on the internal segment.

Inferred attack chain caveat: No public PoC is available in the source data, and no specific shellcode offsets or return-address calculations are disclosed. The chain above is a faithful description of the CWE-119 class and the attack path dictated by the endpoint parameters, not a reproduction of a known exploit binary.

Impact Assessment

Business Impact

• CVSS 9.9 (Critical). Vector breakdown: AV:N — remotely exploitable; AC:L — no race condition, no special conditions; PR:L — low privilege required, but on many embedded devices "low privilege" may map to guest access or default weak credentials; UI:N — no user interaction; S:C — scope change, meaning the compromise can affect resources beyond the vulnerable component (i.e., the rest of the network segment); C:H/I:H/A:H — total confidentiality, integrity, and availability loss on the device.
• Confidentiality: full disclosure of the device configuration, network topology, and any stored credentials (e.g., WPA pre-shared keys).
• Integrity: the attacker can alter SSID, security settings, and route tables, potentially redirecting traffic.
• Availability: the attacker can brick the device by corrupting its firmware or flash, or can use it as a botnet node.

Affected Systems & Blast Radius

Only Comfast CF-N1-S with firmware 2.6.0.1 is explicitly confirmed affected. No other models or firmware versions are listed in the source data. The blast radius extends to: (1) the device itself; (2) the wired and wireless clients connected to it; (3) any DMZ or internal segments the device is bridging. For enterprises, this device is typically a SOHO-grade unit, so exposure is higher in retail, hospitality, remote-office, and home-office environments than in hardened data centers.

Exploit Availability

The NVD description explicitly states the exploit is public. This elevates the practical risk from "theoretical" to "operational," and raises the likelihood of mass scanning and automated exploitation attempts against internet-exposed management interfaces.

Detection Guidance

The detection guidance below targets traffic to the /cgi-bin/mbox-config endpoint with a ptest_ssid section. Because the ssid parameter is a simple string, the detection focuses on the presence of an unusually long ssid value or on shellcode-like content (e.g., long sequences of NOP bytes or obvious binary data) within the query string.

Sigma Rule

title: Comfast CF-N1-S mbox-config ssid Stack Overflow Attempt
id: 5f3a1b2c-8d4e-4f6a-9b1c-2d3e4f5a6b7c
status: experimental
description: Detects HTTP requests to the Comfast CF-N1-S CGI endpoint mbox-config with an abnormally long ssid parameter, indicating a potential stack-based buffer overflow exploit (CVE-2026-77022).
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2026-77022
author: Valters IT Security Research
date: 2026/03/01
logsource:
    product: webserver
    category: webserver
detection:
    selection:
        cs-uri-path|contains: '/cgi-bin/mbox-config'
        cs-uri-query|contains|all:
            - 'method=SET'
            - 'section=ptest_ssid'
            - 'ssid='
    filter_baseline:
        cs-uri-query|len: < 300
    condition: selection and not filter_baseline
level: critical
tags:
    - attack.t1190
    - cve.2026-77022
    - cwe.119
falsepositives:
    - None expected; normal SSID configuration values are short (< 64 bytes per 802.11 spec).

YARA Rule

rule CVE_2026_77022_Comfast_CFN1S_SSID_Overflow
{
    meta:
        author      = "Valters IT Security Research"
        description = "Detects HTTP request payloads targeting Comfast CF-N1-S mbox-config ptst_ssid with oversized ssid parameter (stack overflow CVE-2026-77022)"
        reference   = "https://nvd.nist.gov/vuln/detail/CVE-2026-77022"
        cve         = "2026-77022"
        date        = "2026-03-01"
        score       = 80
    strings:
        $cgi_path = "/cgi-bin/mbox-config" ascii wide
        $method_set = "method=SET" ascii wide
        $section_p = "section=ptest_ssid" ascii wide
        $ssid_param = "ssid=" ascii wide
        $nop_sled = { 00 00 00 00 00 00 00 00 00 00 }   // typical NOP-sled pattern for embedded arch
        $nop2 = { FF FF FF FF FF FF FF FF FF FF }        // alternative padding
        $long_ascii = { 41 41 41 41 41 41 41 41 41 41 }  // 0x41 padding (A*)
    condition:
        uint16(0) == 0x3A47 or uint16(0) == 0x4854  // "GET" or "POST" start of HTTP request
        and all of ($cgi_path, $method_set, $section_p, $ssid_param)
        and ( any of ($nop_sled, $nop2, $long_ascii) )
        and filesize > 300
}

Suricata IDS Rule

alert http any any -> $HOME_NET any (msg:"CVE-2026-77022 Comfast CF-N1-S mbox-config ssid stack overflow attempt"; flow:to_server,established; http.uri; content:"/cgi-bin/mbox-config"; http.uri; content:"method=SET"; http.uri; content:"section=ptest_ssid"; http.uri; content:"ssid="; http.uri; pcre:"/ssid=[^&\s]{100,}/Ui"; reference:cve,2026-77022; classtype:attempted-admin; sid:202677022; rev:1;)

Rationale: The PCRE check enforces ssid= followed by at least 100 characters before the next & or whitespace — exceeding the 802.11 32-byte/64-byte SSID limit and indicating a likely overflow attempt.

Elastic Detection

any where event.category == "web" and url.path == "/cgi-bin/mbox-config"
    and url.query contains "method=SET"
    and url.query contains "section=ptest_ssid"
    and url.query contains "ssid="
    and length(url.query) > 300

Splunk SPL Query

index=web sourcetype=access_combined
| where like(uri_path, "%/cgi-bin/mbox-config%")
    and like(uri_query, "%method=SET%")
    and like(uri_query, "%section=ptest_ssid%")
    and like(uri_query, "%ssid=%")
| eval query_len = len(uri_query)
| where query_len > 300
| stats count by src_ip, dest_ip, uri_query, _time
| sort - count

Wazuh OSSEC Rule

<group name="cve_2026_77022_comfast,">
  <rule id="100622" level="15">
    <if_sid>31122</if_sid> <!-- 31122 is the Apache/HTTP access log decoder rule -->
    <match>\/cgi-bin\/mbox-config</match>
    <regex>method=SET.*section=ptest_ssid.*ssid=</regex>
    <regex>ssid=\S{100,}</regex>
    <description>Comfast CF-N1-S stack buffer overflow attempt via mbox-config ptst_ssid (CVE-2026-77022)</description>
    <group>attack.t1190,cwe.119,cve.2026.77022,</group>
    <mitre>
      <id>T1190</id>
    </mitre>
  </rule>
</group>

Note: The rule ID 100622 is a placeholder for the local environment; operators should assign an unused rule ID. The <if_sid>31122</if_sid> references the standard Wazuh Apache decoder rule ID, which may need adjustment based on the local rule base.

Mitigation & Patch Guidance

Patch Confidence: 0/4 — UNPATCHED.

No patch is available from Comfast or any third party. Neither a vendor advisory, a firmware update, nor a CVE-fix commit has been identified in any tracked source. The organization must assume every CF-N1-S device running 2.6.0.1 is vulnerable until proven otherwise.

1) Immediate Mitigations (apply today)

• Restrict network access to the management interface. If the device is deployed at a branch or SOHO location, ensure the /cgi-bin/mbox-config endpoint is not reachable from the internet. Disable remote management (WAN-side access) in the device configuration.
• Enable an ACL or firewall rule that permits management access only from trusted administrative IPs or a dedicated VLAN.
• Change default/guest credentials immediately. Since the CVSS vector requires PR:L, reducing the likelihood of the attacker obtaining any credential reduces exploitability. Disable guest SSIDs or restrict guest network access to the management VLAN.
• Segment the device from internal assets. Place the CF-N1-S on a separate VLAN with no route to the corporate LAN, minimizing the scope-change (S:C) impact.

2) Patch / Upgrade Steps

• Check for a firmware update from Comfast's official support portal or via the device's update mechanism. Given the patch confidence is 0/4, it is likely none exists at this time. Re-check weekly.
• Contact the vendor (Comfast) directly to request a patch timeline and to verify whether additional firmware versions are affected.
• If no patch is released within a business-acceptable window, decommission the device and replace it with a model from a vendor with a demonstrated security-patch track record (e.g., well-maintained enterprise access points from Cisco, Aruba, or Fortinet).

3) Long-Term Hardening

• Replace the CF-N1-S with a supported enterprise-grade access point that receives regular firmware updates and has a security advisory process.
• Disable the web management interface entirely if the device can be managed via CLI/SSH only; if web management is required, bind it strictly to an internal management interface (e.g., eth1 or a VLAN interface) and block it from the WAN.
• Implement network-level monitoring using the Sigma/Suricata/Elastic rules above to detect exploitation attempts against any remaining vulnerable devices.
• Maintain an asset inventory of all network devices, including firmware versions, to identify exposures rapidly when new CVEs are disclosed.

References

1. NVD Entry — https://nvd.nist.gov/vuln/detail/CVE-2026-77022 (CVE description, CVSS vector, CWE classification)
2. MITRE ATT&CK — https://attack.mitre.org/techniques/T1190/ (Exploit Public-Facing Application — primary tactic)
3. CWE-119 — https://cwe.mitre.org/data/definitions/119.html (Improper Restriction of Operations within the Bounds of a Memory Buffer)
4. Comfast Official Portal — https://www.comfast.com (vendor site — monitor for firmware advisory; no fix published as of report date)
5. FIRST.org EPSS — https://www.first.org/epss/ (EPSS not yet scored for this CVE; re-check regularly)

Threat Actor / Campaign Notes: No specific threat-actor campaigns, ransomware groups, or known exploit-in-the-wild evidence are attributed to this CVE in the provided data. However, the public availability of an exploit combined with the high CVSS score (9.9) and the device's typical placement at the network edge makes it an attractive target for opportunistic botnets and exposure-scanning tools. Organizations running this device should treat any internet-exposed management interface as actively endangered.