CVE-2024-41340

Executive Summary

CVE-2024-41340 is an arbitrary code execution vulnerability affecting the APP Enforcement module upload functionality in a wide range of Draytek Vigor router models, including the Vigor 165/166, 2620/LTE200, 2860/2925, 2862/2926, 2133/2762/2832, 2135/2765/2766, 2865/2866/2927, 2962/3910, and 3912 series. An attacker who reaches the device's management interface can upload a crafted APP Enforcement module, resulting in arbitrary code execution on the router's firmware. There is currently no confirmed vendor patch (patch confidence 0/4), no public PoC, and the CVE is not listed in CISA KEV; however, the affected devices are commonly deployed as perimeter/VPN gateways in SMB and telecommuter environments, making successful exploitation high-impact.

Technical Analysis

The NVD description for CVE-2024-41340 is sparse and does not disclose specific implementation details such as function names, HTTP endpoints, or upload parameters. What is explicitly stated is that the flaw exists in the processing of "APP Enforcement" modules — the application/content-filtering rule engine used by Draytek Vigor routers — and that uploading a crafted module leads to arbitrary code execution.

The vulnerability belongs to the class of unrestricted upload of a file with dangerous type (CWE-434). In this mechanism, the firmware's module import routine fails to adequately validate or sanitize the uploaded APP Enforcement module before it is parsed and installed. Because the module parser executes within the router's control-plane runtime with elevated privileges, an uploaded file can carry embedded executable code that is invoked during parsing, registration, or activation of the APP Enforcement signature set. The result is remote code execution in the context of the router firmware — typically full device compromise, since no privilege boundary exists between the module loader and the underlying operating environment.

Attack surface: the primary entry point is the router's web-based management interface, which is reachable over HTTP/HTTPS. Many Vigor deployments expose the management interface on the WAN side or on VPN-provisioned subnets, which broadens the exploitable reach. The NVD description does not state whether authentication is required before the vulnerable upload function is reachable; if the upload routine is accessible pre-authentication, exposure is severe; if it requires an authenticated administrative session, attackers would need credentials (e.g., default or weak credentials, or credential theft) as a prerequisite. Sufficient technical detail is not available to resolve this distinction, so both paths must be considered.

Firmware version spread is broad: the advisory lists per-model vulnerable boundaries ranging from v3.9.6 up to v4.4.5.3, indicating the flaw was present across multiple maintenance branches and was only recently rectified (if at all) in the versions implied by the description. Notably, patch confidence is 0/4, meaning no tracked source — vendor advisory, changelog, or security bulletin — has confirmed remediation, despite the version boundaries implied by the CVE text. This inconsistency suggests the fix status should be verified directly against Draytek's release notes before assuming any given firmware build is safe.

Exploitation Scenarios

No public PoC or exploit code has been identified for CVE-2024-41340. The attack chain below is inferred strictly from the vulnerability class (crafted module upload → arbitrary code execution) and from the affected product's typical deployment as an Internet-facing network gateway.

1. Reconnaissance / target identification: The attacker scans for exposed Draytek Vigor devices using Internet-wide search engines (e.g., Shodan queries such as http.title:"Vigor" or http.html:"DrayTek"). The management login page or HTTP response headers are used to fingerprint the device model and firmware version. Targets running a vulnerable firmware version from the affected range are selected. If the management interface is not directly Internet-exposed, the attacker may first compromise a host on the LAN or VPN segment from which the management interface is reachable.

2. Triggering the vulnerability: The attacker submits a crafted APP Enforcement module through the management interface's module upload function. Because the module is a structured binary object and the import routine lacks sufficient validation (CWE-434), the malicious module is accepted and processed. If authentication is enforced on the upload function, this step requires valid administrator credentials — potentially obtained via default credentials, credential reuse, brute force, or a previous compromise of an administrative workstation.

3. Payload / execution method: The crafted module embeds executable content alongside (or in place of) legitimate APP Enforcement rule data. When the router parses and installs the module — which occurs automatically upon upload or on the next enforcement engine reload — the embedded code executes on the device's control plane. The resulting execution context is the router firmware itself, providing attacker-controlled code with the device's full privileges. Specific payload construction details are not publicly documented for this CVE; the exact encoding, magic bytes, or injection technique used to convert a module file into executable instructions cannot be confirmed from available data.

4. Post-exploitation impact: With code execution on the gateway, the attacker gains persistent presence on the network perimeter. Typical follow-on actions include: intercepting or redirecting LAN and VPN traffic; harvesting credentials from captured plaintext sessions; modifying DNS or routing tables for phishing or man-in-the-middle campaigns; reconfiguring firewall rules to expose internal hosts; using the device as a relay/proxy to mask further malicious activity; and bricking the device to cause denial of service. Because Vigor routers are frequently used as VPN endpoints for remote workers and branch offices, a compromise may expose the entire VPN trust boundary.

Impact Assessment

Business impact is high for affected organizations. Draytek Vigor devices are typically deployed as the primary Internet gateway, firewall, and VPN concentrator for small-to-medium businesses, branch offices, and telecommuters. Arbitrary code execution on such a device surrenders the network perimeter to the attacker: confidentiality is lost (traffic inspection, credential harvesting), integrity is lost (route/DNS/firewall manipulation), and availability is at risk (device bricking or reconfiguration).

Blast radius extends beyond the router itself: the LAN behind the device, all VPN sessions terminating at the device, and any networks reachable through the device's routing table become potentially accessible to the attacker. In multi-site deployments, a compromised site gateway can be used to pivot toward the corporate WAN.

Risk scoring context: the NVD entry provides no CVSS score or vector (CVSS: N/A), and no CWE is assigned in the CVE data — the CWE-434 classification used in this report is inferred from the described mechanism, not vendor-supplied. The EPSS score of 0.00211 (11.7th percentile of exploited CVEs) indicates a low probability of mass exploitation in the short term; however, EPSS measures opportunistic exploit likelihood, not campaign-level risk from targeted attackers. The vulnerability is not listed in CISA's Known Exploited Vulnerabilities catalog (KEV: NO), and no in-the-wild exploitation evidence was present in the provided data. Targeted attacks against exposed VPN gateways remain a realistic threat regardless of EPSS, particularly in regions and sectors where Draytek equipment is prevalent.

Detection Guidance

Detection rules below are generic signatures built from the vulnerability class (multipart/form-data module upload to Draytek Vigor management interfaces) because the NVD description discloses no HTTP endpoints, parameter names, or file-format specifics. Tune these rules to your environment and validate against legitimate firmware/APP Enforcement update traffic, which may produce similar upload patterns.

Sigma Rule

title: Potential Draytek Vigor APP Enforcement Module Upload Attempt (CVE-2024-41340)
id: b6a1e491-3c0a-4f6e-9b4d-2c7b9e3d5a01
status: experimental
description: >
  Detects HTTP POST requests with multipart/form-data content addressed to Draytek
  Vigor management interfaces, consistent with the crafted APP Enforcement module
  upload flaw described in CVE-2024-41340.
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2024-41340
author: vartersit.com Threat Intelligence
date: 2024/07/01
logsource:
    category: webserver
    product: generic
detection:
    selection_method:
        http.method: POST
    selection_upload:
        http.content_type|startswith: multipart/form-data
    selection_target:
        http.host|contains:
            - vigor
            - draytek
    selection_server:
        http.response.headers.server|contains:
            - Vigor
            - DrayTek
    condition: selection_method and selection_upload and (selection_target or selection_server)
falsepositives:
    - Legitimate APP Enforcement signature or firmware updates performed by administrators
level: high

YARA Rule

rule CVE_2024_41340_Draytek_Crafted_APP_Module
{
    meta:
        author = "vartersit.com Threat Intelligence"
        description = "Detects binary artifacts consistent with crafted Draytek APP Enforcement modules used to exploit CVE-2024-41340"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2024-41340"
        date = "2024-07-01"
    strings:
        $s1 = "DrayTek" ascii wide nocase
        $s2 = "APP Enforcement" ascii wide nocase
        $s3 = "APPEnforce" ascii wide nocase
        $x1 = { 4D 5A }                     /* MZ header - PE executable */
        $x2 = { 7F 45 4C 46 }               /* ELF magic - ELF executable */
        $x3 = { 23 21 }                     /* shebang - script payload */
    condition:
        uint16(0) == 0x5A4D or uint32(0) == 0x464C457F or
        (any of ($s1, $s2, $s3) and any of ($x1, $x2, $x3))
}

Suricata IDS Rule

alert http $EXTERNAL_NET any -> $HOME_NET any (msg:"ET EXPLOIT Possible Draytek Vigor APP Enforcement Module Upload Attempt (CVE-2024-41340)"; flow:established,to_server; http.method; content:"POST"; http.content_type; content:"multipart/form-data"; http.host; content:"vigor"; nocase; file.data; content:"APP Enforcement"; nocase; reference:url,https://nvd.nist.gov/vuln/detail/CVE-2024-41340; classtype:attempted-admin; sid:202441340; rev:1;)

alert http any any -> any any (msg:"ET SCAN Draytek Vigor Management Interface Identified (CVE-2024-41340 Exposure)"; flow:established,to_server; http.server; content:"Vigor"; nocase; reference:url,https://nvd.nist.gov/vuln/detail/CVE-2024-41340; classtype:web-application-activity; sid:202441341; rev:1;)

Elastic Detection

sequence by destination.ip with maxspan=2m
  [ http where http.response.status_code == 200 and
      (http.response.headers.server like "*Vigor*" or
       http.response.headers.server like "*DrayTek*") ]
  [ http where http.request.method == "POST" and
      startsWith(http.request.body.content, "multipart/form-data") ]

Splunk SPL Query

index=* (sourcetype="access_combined" OR sourcetype="suricata:http" OR sourcetype="pan:traffic")
  http_method=POST http_content_type="multipart/form-data*"
  (host=*vigor* OR host=*draytek* OR server=*Vigor* OR uri_path=*vigor*)
  | stats count AS attempts, values(uri) AS uploaded_uri, dc(src_ip) AS distinct_sources
          BY dest_ip, host, _time
  | where attempts > 0
  | eval alert=if(attempts>=3, "HIGH", "MEDIUM")
  | table _time, src_ip, dest_ip, host, uploaded_uri, http_content_type, attempts, alert
  | sort - attempts

Wazuh OSSEC Rule

<group name="web,attack,">
  <rule id="100401" level="12">
    <if_sid>31100</if_sid>
    <method>POST</method>
    <match>multipart/form-data</match>
    <regex>(\bVigor\b|\bDrayTek\b)</regex>
    <description>CVE-2024-41340: Attempted APP Enforcement module upload to Draytek Vigor management interface.</description>
    <group>web_application_attack,pci_dss_6.5,gdpr_32,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence for CVE-2024-41340 is 0/4 — no patch evidence has been confirmed from any tracked source, and the CVE data lists no vendor fix or workarounds. Until an official advisory is published, treat all listed vulnerable firmware branches as exposed.

Immediate mitigations:

• Restrict access to the management interface to trusted administrative hosts/subnets only; do not expose it directly to the WAN unless absolutely required. Use firewall rules to limit source IPs.
• Disable WAN-side management (HTTP/HTTPS) if enabled; requiring management via LAN or VPN substantially reduces the exploitable attack surface.
• Change all administrative credentials to strong, unique values and ensure default credentials are not in use.
• Monitor the management interface logs for unexpected uploads of APP Enforcement modules, especially from unrecognized IPs or outside maintenance windows.
• If the management interface must be exposed, place an upstream WAF/reverse proxy that blocks multipart/form-data POST requests to the device by default and alerts on anomalies.

Patch / upgrade steps:

• No official patch is confirmed. The firmware versions implied as fixed by the NVD description are: Vigor 165/166 ≥ 4.2.6; Vigor 2620/LTE200 ≥ 3.9.8.8; Vigor 2860/2925 ≥ 3.9.7; Vigor 2862/2926 ≥ 3.9.9.4; Vigor 2133/2762/2832 ≥ 3.9.8; Vigor 2135/2765/2766 ≥ 4.4.5.1; Vigor 2865/2866/2927 ≥ 4.4.5.3; Vigor 2962/3910 ≥ 4.3.2.7; Vigor 3912 ≥ 4.3.5.2.
• Before upgrading, verify against Draytek's official firmware release notes and security advisories that the target build actually contains the fix — do not assume, since patch confidence remains 0/4.
• After upgrading, validate firmware integrity and re-confirm hardened management settings persist across the upgrade.

Long-term hardening:

• Replace any end-of-life Vigor models that will never receive a firmware fix.
• Implement centralized logging of router management events to a SIEM and apply the detection rules above.
• Segment the management plane onto a dedicated VLAN; enforce strong multi-factor authentication where supported.
• Establish a firmware baseline and integrity-checking process so unauthorized module/firmware changes are flagged.
• Periodically re-assess Internet exposure of all perimeter devices using the provided Shodan-style dorks.

References

• NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2024-41340
• MITRE CVE Record: https://www.cve.org/CVERecord?id=CVE-2024-41340
• Draytek Official Support Portal (vendor advisories/firmware; specific advisory not confirmed): https://www.draytek.com/support/
• FIRST EPSS (score data): https://www.first.org/epss/
• CISA Known Exploited Vulnerabilities Catalog (CVE not listed as of analysis date): https://www.cisa.gov/known-exploited-vulnerabilities-catalog

No known threat-actor campaigns or exploit-in-the-wild evidence were identified in the provided intelligence data. PoC availability remains unknown, and no exploit code was found in tracked sources.