CVE-2026-77148

Executive Summary

CVE-2026-77148 is a critical stack-based buffer overflow vulnerability (CWE-119) discovered in Comfast CF-N1-S wireless router firmware version 2.6.0.1, specifically within the Web Management component accessible via the /cgi-bin/mbox-config endpoint. The vulnerability is remotely exploitable via crafted requests to the ptest_channel configuration section, leading to arbitrary code execution with high privileges on affected devices. With a CVSS score of 9.9, this vulnerability poses an immediate threat to all Comfast CF-N1-S devices running the affected firmware, which are typically deployed as edge wireless routers in small office and home environments. The exploit has been made public, increasing the risk of mass exploitation by opportunistic threat actors.

Technical Analysis

The vulnerability resides in the function sub_44B50C located within the file /cgi-bin/mbox-config of the Comfast CF-N1-S router's Web Management interface. This function is invoked when a request is made using the HTTP parameters method=SET and section=ptest_channel. The affected code path processes user-supplied input destined for the ptest_channel configuration section.

The root cause is a classic stack-based buffer overflow. When the CGI handler receives data for the ptest_channel section, it copies the input into a fixed-size stack buffer without performing proper bounds checking or length validation. By supplying an input payload exceeding the buffer's allocated capacity, an attacker can overwrite adjacent memory on the call stack. This includes saved return addresses, stack frame pointers, and potentially local variables used for control flow decisions.

Stack-based buffer overflows of this nature are particularly dangerous in embedded networking devices for several reasons. First, embedded processors such as MIPS or ARM (commonly found in routers) often have non-executable stack protections (NX) disabled or inconsistently enforced, making straightforward return-address overwrites and shellcode execution feasible. Second, these devices frequently lack modern memory corruption mitigations such as stack canaries, ASLR, or RELRO, leaving the overflow primitive directly exploitable. Third, the attack surface is exposed on the network: the CGI endpoint is reachable via HTTP, and authentication could potentially be bypassed or default credentials may be in use given the low privilege requirement (PR:L) in the CVSS vector.

The fact that the exploit has been made public suggests that security researchers have not only confirmed the crash but have likely developed reliable exploitation techniques for the MIPS/ARM architecture, leveraging ret2libc or ROP (Return-Oriented Programming) chains to achieve code execution. The method=SET parameter indicates the handler processes state-changing actions, meaning the overflow occurs during a write operation rather than a read, which is typically easier to leverage for arbitrary memory corruption.

The CVSS vector provides additional insight into the vulnerability's characteristics:

• Attack Vector (AV:N): Remote exploitation over the network without physical access
• Attack Complexity (AC:L): No special conditions or race conditions required for exploitation
• Privileges Required (PR:L): Low-level authentication or access is required, suggesting default credentials may be sufficient
• User Interaction (UI:N): No victim interaction needed
• Scope (S:C): The compromise extends beyond the vulnerable component, impacting the entire device
• Confidentiality/Integrity/Availability (C:H/I:H/A:H): Complete compromise of device confidentiality, integrity, and availability

Insufficient technical detail is available in the public description regarding the exact buffer size, the precise offset of the overwrite, or the underlying processor architecture. This information would typically require the full exploit code or a detailed vulnerability analysis whitepaper.

Exploitation Scenarios

The attack chain for CVE-2026-77148 follows a logical progression from target identification to full device compromise:

Step 1: Reconnaissance and Target Identification

Attackers would first identify Comfast CF-N1-S devices exposed to the internet. The device's Web Management interface typically listens on standard HTTP ports (80, 8080, or 8000). Shodan and other internet-wide scanning tools can be used to locate devices by matching the HTTP Title responses or specific device fingerprints in page content. Network banners and default landing pages of Comfast devices often contain identifiable strings that allow fingerprinting. Given that PR:L is required, the attacker would also need valid credentials — Comfast devices frequently ship with default credentials (such as admin/admin) that are rarely changed by end users.

Step 2: Triggering the Vulnerability

The attacker sends a crafted HTTP request to the vulnerable endpoint: /cgi-bin/mbox-config?method=SET&section=ptest_channel. The request body or parameters contain a malicious payload that exceeds the bounds of the stack buffer in function sub_44B50C. The payload would typically consist of:

• Padding bytes to fill the legitimate buffer space
• An overflow segment containing the malicious return address or ROP chain
• Optional: shellcode for immediate execution

The request must be properly formatted for the CGI handler to route it to the vulnerable code path — using the method=SET parameter to trigger the write operation and section=ptest_channel to reach the vulnerable function's specific code branch.

Step 3: Payload Execution

Upon successful overflow, control flow is redirected to attacker-controlled code. On embedded MIPS/ARM architectures, this commonly manifests as:

• Direct stack shellcode execution if NX is not enforced
• ROP chains that call system functions like system() with a command string
• Return-to-libc attacks targeting system("telnetd -l /bin/sh") or similar to spawn a reverse shell

The attacker achieves Remote Code Execution (RCE) with the privileges of the web server process, which on these routers typically runs as root.

Step 4: Post-Exploitation Impact

Once code execution is achieved, the attacker can:

• Install persistent backdoors by modifying firmware partitions or adding startup scripts
• Harvest Wi-Fi credentials, WPA2/3 pre-shared keys, and network configuration data
• Use the compromised device as a proxy or relay for further network intrusions
• Perform lateral movement to other devices on the LAN segment
• Turn the router into a zombie for botnet recruitment (e.g., Mirai-style IoT botnets)

No public PoC or exploit code has been disclosed at the time of this report; however, the exploit has been described as "made public," indicating that details are circulating in the security community. The attack chain is inferred from the vulnerability class and standard exploitation techniques for embedded devices.

Impact Assessment

The business impact of CVE-2026-77148 is severe, reflected by its near-maximum CVSS score of 9.9. The vulnerability is rated Critical with the following subscores contributing to the aggregate:

• Confidentiality Impact: High — Full disclosure of device configuration, credentials, network topology, and communicated traffic
• Integrity Impact: High — Complete ability to modify device behavior, inject malicious configurations, or alter routing decision
• Availability Impact: High — Ability to brick devices, cause denial of service, or disrupt network connectivity
• Scope: Changed — Compromise extends beyond the Web Management component to the entire device and potentially the LAN it serves

Affected systems are Comfast CF-N1-S devices running firmware version 2.6.0.1. These devices are positioned as budget-friendly wireless routers and access points, commonly deployed in:

• Small and home offices (SOHO)
• Guest Wi-Fi deployments in hospitality
• Temporary event networking
• Remote site connectivity in branch offices

The blast radius of exploitation extends beyond the device itself. A compromised router provides a foothold in the internal network, enabling:

• Man-in-the-middle attacks on all LAN traffic
• DNS hijacking to redirect users to phishing sites
• Pivoting to internal servers and workstations
• Physical network segmentation bypass

The publication of exploit details combined with the low complexity of exploitation and the lack of available patches transforms this from a theoretical risk to an active threat. Given the device's internet-facing management interface, any organization using Comfast CF-N1-S devices should consider them fully compromised until proven otherwise.

Detection Guidance

The following detection rules are designed to identify exploitation attempts targeting CVE-2026-77148. Since the vulnerability triggers on HTTP requests to the mbox-config endpoint with the ptest_channel section, detection focuses on suspicious request patterns to this endpoint.

Sigma Rule

title: Comfast CF-N1-S mbox-config Buffer Overflow Exploitation
id: c1e4e0b2-5a44-4ac0-9e88-7a2e13312345
status: experimental
description: Detects HTTP requests targeting the Comfast mbox-config endpoint with ptest_channel section parameter, potentially indicating exploitation of CVE-2026-77148.
date: 2026/02/15
author: Valtersit Threat Intelligence
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2026-77148
tags:
    - attack.initial-access
    - attack.t1190
    - cve.2026-77148
logsource:
    category: webserver
    product: apache
    definition: HTTP server access logs or WAF logs
detection:
    selection:
        cs-method: 'GET' # or POST, depending on CGI implementation
        cs-uri-query|contains|all:
            - 'method=SET'
            - 'section=ptest_channel'
        cs-uri-stem: '/cgi-bin/mbox-config'
    condition: selection
    timeframe: 5m
falsepositives:
    - Legitimate administrative configuration changes to channel testing features
level: high

YARA Rule

rule Comfast_CF_N1_S_CVE_2026_77148_Exploit
{
    meta:
        author = "Valtersit Threat Intelligence"
        description = "Detects payloads targeting Comfast CF-N1-S mbox-config buffer overflow CVE-2026-77148"
        date = "2026-02-15"
        reference = "CVE-2026-77148"
        severity = "critical"
    strings:
        $endpoint1 = "/cgi-bin/mbox-config" ascii wide
        $endpoint2 = "method=SET" ascii wide
        $endpoint3 = "section=ptest_channel" ascii wide
        // Typical MIPS NOP-sled patterns (0x2404xxxx or similar MIPS instructions)
        $mips_nop1 = { 00 00 00 00 }
        $mips_nop2 = { FF FF 00 00 }
        $rop_chain = { 2C ?? ?? ?? 28 ?? ?? ?? } // Common MIPS ROP gadgets
        $shellcode1 = "/bin/sh" ascii
        $shellcode2 = "telnetd" ascii
        $shellcode3 = "wget" ascii
    condition:
        2 of ($endpoint*) and 1 of ($shellcode*) and (
            uint16(0) == 0x8900 or // Potential MIPS header
            $mips_nop1 or
            $mips_nop2 or
            $rop_chain
        )
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-77148 Comfast mbox-config buffer overflow attempt"; flow:to_server,established; http.uri; content:"/cgi-bin/mbox-config"; http.uri; content:"method=SET"; http.uri; content:"section=ptest_channel"; content:"|41 41 41 41|"; within:8000; threshold:type limit, track by_src, count 5, seconds 60; reference:cve,2026-77148; classtype:attempted-admin; sid:77777148; rev:1;)

Elastic Detection

sequence by source.ip
  [network where process.name == "httpd" and event.outcome == "failure"
     and dns.question.name == "" ] // Placeholder for DNS
  [http where request.method in ("GET", "POST") and request.uri.path == "/cgi-bin/mbox-config"
     and request.uri.query contains "method=SET"
     and request.uri.query contains "section=ptest_channel"
     and request.uri.query has substring "A"*500] // Indicates long payload

// Alternative simpler rule:
any where http.request.method in ("GET", "POST") and
    url.path == "/cgi-bin/mbox-config" and
    query_string contains "method=SET" and
    query_string contains "section=ptest_channel" and
    (event.category == "web" or event.dataset == "apache.access")

Splunk SPL Query

index=web sourcetype=access_combined uri_path="/cgi-bin/mbox-config"
| regex uri_query="method=SET"
| regex uri_query="section=ptest_channel"
| eval payload_length=len(uri_query)
| search payload_length > 500
| stats count by src_ip uri_query status
| where count > 5
| sort -count

Or for raw network traffic capture:

index=netflow sourcetype=cisco:netflow 
| search dest_port=80
| table src_ip dest_ip bytes

Wazuh OSSEC Rule

<group name="webserver,">
  <rule id="973581" level="15">
    <decoded>umode</decoded>
    <match>method=SET</match>
    <match>section=ptest_channel</match>
    <match>/cgi-bin/mbox-config</match>
    <description>CVE-2026-77148 - Comfast CF-N1-S mbox-config stack buffer overflow exploitation attempt</description>
    <group>comfast,cve,2026-77148,exploitation,</group>
    <mitre>
      <id>T1190</id>
    </mitre>
  </rule>
</group>

Detection considerations: These rules focus on the unique combination of the request path and parameters specific to the vulnerable endpoint. Given that this is a stack-overflow vulnerability, an increase in request size beyond normal parameters is a strong indicator. Monitor for repeated requests from the same source IP, which may indicate brute-force or fuzzing activity. Additionally, correlating successful HTTP responses (200/302) with subsequent anomalous outbound connections from the device can signal successful compromise and callback activity.

Mitigation & Patch Guidance

Patch confidence assessment: No patch evidence has been identified from any tracked source. The vendor has not released a fix or advisory. Until a patch becomes available, treat all Comfast CF-N1-S devices running version 2.6.0.1 as vulnerable and prioritize isolation or replacement.

References

1. NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2026-77148 — Official NVD record with CVSS scoring and description
2. CWE-119 Entry: https://cwe.mitre.org/data/definitions/119.html — MITRE's description of the buffer overflow weakness class
3. Shodan IoT Search: https://www.shodan.io/search?query=http.title%3A%22Comfast%22 — Device exposure tracking (may require account)
4. FIRST EPSS: https://www.first.org/epss/ — For updated EPSS scoring when available (currently un-scored)
5. CISA Known Exploited Vulnerabilities: https://www.cisa.gov/known-exploited-vulnerabilities-catalog — Monitor for inclusion if in-the-wild exploitation is confirmed

Threat actor context: At the time of writing, no specific threat actor campaigns have been publicly attributed to this vulnerability. However, the public disclosure of the exploit mechanism significantly lowers the barrier to entry for opportunistic attackers and IoT botnet operators. Historically, similar router vulnerabilities have been weaponized within days of public disclosure by botnet campaigns (e.g., Mirai variants). Organizations using Comfast CF-N1-S devices should assume active exploitation attempts are imminent or already occurring.