CVE-2026-86300

Executive Summary

CVE-2026-86300 is an authentication bypass vulnerability affecting the Tenda AC9 wireless router, specifically firmware version 15.03.05.14. The flaw resides within the Web Management component, where the function R7WebsSecurityHandler fails to enforce proper authentication, allowing unauthenticated remote attackers to interact with administrative HTTP interfaces. Successful exploitation could result in unauthorized access to management functions, configuration modification, or traffic interception. Given a CVSS score of 7.3 (High) and an unavailable patch, Tenda AC9 devices running this firmware should be considered at immediate risk if exposed to untrusted networks.

Technical Analysis

The vulnerability is located in the Tenda AC9 router's Web Management HTTP interface, specifically within a handler function referenced as R7WebsSecurityHandler. Based on the vulnerability class (CWE-287 — Improper Authentication), the handler fails to properly validate whether an incoming HTTP request originates from an authenticated administrative session.

The attack vector is network-based (AV:N), requiring no privileges (PR:N) and no user interaction (UI:N). The lack of an authentication check means that any network actor who can reach the router's management web service (typically TCP port 80 or 443) can invoke the handler directly with crafted HTTP requests. The CWE-287 classification indicates the software either does not perform an authentication check at all for certain code paths, or performs an incorrect check that can be bypassed.

Data from the NVD description confirms that an exploit "has been published and may be used," indicating that exploitation techniques are publicly available in some form, even though no dedicated PoC file or Nuclei template is indexed in the provided dataset. The affected function name R7WebsSecurityHandler is the only implementation detail disclosed; specific URL paths, parameters, or request structures are not provided in the NVD record.

Insufficient technical detail is available in the public advisory to provide a code-level examination of the exact authentication bypass mechanism (e.g., whether it is a logic flaw, missing session check, or cookie manipulation). Analysts should treat the vulnerable code path as any unauthenticated request reaching the web management handler.

Exploitation Scenarios

Because an exploit is confirmed published but no specific implementation details are disclosed, the attack chain below is inferred from the vulnerability class and the affected component. No public PoC is available in the indexed dataset; the attack chain is inferred from vulnerability class dynamics.

Step 1 — Reconnaissance and Target Identification: An attacker scans for Tenda AC9 devices on the internet or a local network using network enumeration tools. Shodan-style queries such as http.title:"AC9" or product:"Tenda AC9" can identify exposed admin panels, typically listening on TCP port 80/443. The admin web interface is customarily left on the LAN side, but misconfigured UPnP or port-forwarding rules may expose it to the WAN.

Step 2 — Triggering the Authentication Bypass: The attacker crafts a direct HTTP request to the router's web management interface. Because the R7WebsSecurityHandler function improperly authenticates requests, the attacker sends a request without presenting valid session cookies or basic-auth credentials. The vulnerable code path accepts the request and processes it as if an authenticated administrator had issued it.

Step 3 — Payload Execution at the Vulnerability-Class Level: Since this is an authentication bypass, no injection payload is required. The attacker leverages the flaw by issuing standard administrative HTTP calls (e.g., a request to alter settings or retrieve configuration). The exact URL endpoints are not documented in the public advisory, but common management operations on Tenda routers include WiFi configuration changes, admin password resets, or firmware update triggers.

Step 4 — Post-Exploitation Impact: With administrative control, the attacker can:

• Change the router's DNS settings to redirect traffic to malicious servers (DNS hijacking for credential phishing),
• Alter firewall or port-forwarding rules to expose internal services,
• Reconfigure the WiFi network to capture traffic,
• Install a modified firmware image if the update mechanism is accessible,
• Harvest any credentials previously entered into the management UI.

The CVSS sub-scores corroborate a limited but broad impact: LOW confidentiality impact (C:L) suggests basic information disclosure, LOW integrity (I:L) permits configuration tampering, and LOW availability (A:L) indicates potential for disruption — the attacker does not gain full system control but can modify network behavior.

Impact Assessment

Affected Systems: Tenda AC9 routers running firmware version 15.03.05.14. The vendor has not announced patch availability; patch confidence is 0/4 across all tracked sources. No alternative affected versions are formally listed, but other firmware builds of the AC9 may share the vulnerable code path until differentially proven otherwise.

Business Impact: For home and small-office environments, this vulnerability enables an external attacker to take control of the network gateway, intercept DNS traffic, and pivot toward internal clients. For enterprises that use SOHO routers in remote offices or retail locations, the threat is escalated because the device may represent the only network boundary protecting internal systems.

Blast Radius: The router is the single point of control for all inbound and outbound traffic. Compromise means the confidentiality and integrity of all traversing traffic in and out of the premises is at risk, particularly if DNS or DHCP settings are modified. The "UNPATCHED" status combined with a published exploit indicates active exploitation risk that is likely to increase in the near term, though no CISA KEV listing or observed threat-actor campaign is documented in the provided data.

Detection Guidance

Detection of this vulnerability is complicated by the fact that exploitation involves ordinary, well-formed HTTP requests — the unauthorised nature is only apparent from session state, not from the payload itself. Correlating a request without session cookies to administrative handlers is the strongest baseline signal.

Sigma Rule

title: Tenda AC9 Web Management - Unauthenticated Access to R7WebsSecurityHandler
id: 3f7a1c9e-8f2b-4a6d-9e4c-1b8d2f0a6c34
status: experimental
description: Detects HTTP requests to Tenda AC9 admin interface originating without prior authentication/session cookie, targeting the R7WebsSecurityHandler path.
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2026-86300
author: ValtersIT SOC
date: 2026/05/15
logsource:
    category: webserver
    product: tenda
detection:
    selection_root:
        cs-method: 'GET'
        cs-uri-extension: '/'
        cs-host: '192.168.0.1' # typical Tenda admin IP, adjust as needed
        cs-user-agent: '*' 
    selection_handler:
        # If the endpoint path is observable, match it.
        cs-uri-query|contains: 
            - 'R7WebsSecurityHandler'
            - 'security'
    selection_unauth:
        # No session token or clear administrative cookie present
        cs-cookie: 
            - null
            - ''
    condition: selection_root and selection_handler and selection_unauth
    timeframe: 5m
level: high
falsepositives:
    - Devices where a reverse proxy strips cookie headers before logging
    - First-time admin logins where the session cookie is only set after the first response
fields:
    - clientip
    - cs-host
    - cs-uri-stem
    - cs-cookie
tags:
    - attack.initial_access
    - attack.t1190
    - cve.2026.86300

YARA Rule

rule CVE_2026_86300_Tenda_AC9_ExploitTraffic
{
    meta:
        author = "ValtersIT SOC"
        description = "Detects HTTP payload strings and URI patterns commonly associated with CVE-2026-86300 exploitation attempts against Tenda AC9 devices"
        date = "2026-05-15"
        cve = "CVE-2026-86300"
        severity = "high"
    strings:
        $a = "R7WebsSecurityHandler" ascii wide nocase
        $b = "Tenda AC9" ascii wide nocase
        $c = "loginAuth" ascii wide nocase
        $d = "setWanSetting" ascii wide nocase
        $e = "goform" ascii wide nocase
        $f = "0.0.0.0" ascii wide nocase
    condition:
        (uint16(0) == 0x5A4D or uint16(0) == 0x4D5A) and  // PE file
        all of them
}

Note: YARA is generally used for file scanning. The above rule is intended for forensic triage if a PCAP containing the exploit traffic is converted to a file stream, or for scanning captured network dumps.

Suricata IDS Rule

alert http any any -> $HOME_NET any (msg:"CVE-2026-86300 Tenda AC9 - Unauthenticated Access Attempt"; flow:to_server,established; content:"GET"; http_method; content:"R7WebsSecurityHandler"; http_uri; content:"Host"; http_header; pcre:"/^Referer:\s*http:\/\/[^\/]+\/main\.htm/Hi"; classtype:attempted-admin; sid:2026863001; rev:1; priority:1;)

Elastic Detection

sequence by source.ip with maxspan=1m
  [ network where
      destination.port in (80, 443) and
      network.protocol == "http" and
      url.path : "*R7WebsSecurityHandler*"
  ]
  [ authentication where
      host.name : "*tenda*" and
      event.action == "authentication_failed" and
      user.name == null
  ]

Splunk SPL Query

index=web sourcetype=access_combined
| where like(uri_path, "%R7WebsSecurityHandler%")
| eval has_cookie = if(isnull(cookie) OR cookie="", "no", "yes")
| where has_cookie="no"
| table _time, clientip, uri_path, uri_query, http_user_agent, cookie
| sort -_time
| stats count by clientip
| where count > 5

Wazuh OSSEC Rule

<group name="tenda_unauth,">
    <rule id="100320" level="15">
        <if_sid>31100</if_sid>
        <match>R7WebsSecurityHandler</match>
        <description>Tenda AC9 CVE-2026-86300 - Unauthenticated request to Web management security handler</description>
        <group>attacks,</group>
        <mitre>
            <id>T1190</id>
        </mitre>
    </rule>
</group>

Additional Detection Considerations

• Look for malformed HTTP requests to the management interface (e.g., missing User-Agent or other standard headers) that complete successfully and return a 200 OK with administrative content.
• Monitor for configuration change logs on the router: sudden changes to DNS settings, admin username/password, or WiFi SSID/password without a corresponding interactive admin session can be a post-exploitation signature.
• Correlate any inbound external IP accessing the management interface with geo-threat-intel feeds; the attack surface is exclusively network-facing.

Mitigation & Patch Guidance

Patch Status: No vendor patch is available (patch confidence 0/4). The vendor (Tenda) has not released an advisory or updated firmware for version 15.03.05.14 as of the data cutoff. CVE-2026-86300 is listed as UNPATCHED — do not delay protection awaiting an official fix.

1) Immediate Mitigations (apply today):

• Restrict management interface access to trusted LAN IPs only. If remote administration is required, use a VPN tunnel rather than direct exposure.
• Configure the router's firewall to drop inbound traffic to TCP ports 80, 443, and 8080 from the WAN side.
• Disable remote management (Admin Via WAN) in the administration settings if present.
• Change the default admin credentials immediately; a compromised weak password combined with an auth bypass nullifies any protection.
• Place the router behind a dedicated edge firewall or enable SPI (Stateful Packet Inspection) rules in an upstream device to control access to the router's IP.
• Monitor router logs for unrecognized configuration changes or login attempts.

2) Patch and Upgrade Steps (when available):

• Periodically check Tenda's official support site and firmware download pages for an AC9 update that addresses this CVE.
• If the device is EOL (end-of-life) and no firmware is forthcoming from the vendor, plan immediate replacement with a current-generation router that receives active security support.
• When a patched firmware is released, update from a trusted workstation connected via Ethernet cable. Verify firmware checksums published by the vendor.

3) Long-Term Hardening:

• Segregate IoT/SOHO network devices into a separate VLAN from business-critical systems so that router compromise does not automatically expose internal corporate endpoints.
• Implement network-level intrusion detection at the network perimeter that can flag administrative web sessions originating from unexpected IPs.
• Add the device to a configuration management process that detects drift from baseline settings (e.g., DNS IP changes, unknown port-forward rules).
• Document a replacement lifecycle for SOHO network equipment, typically 3–5 years from manufacturing, and enforce firmware currency checks quarterly.

References

• NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2026-86300 — Official NVD record containing the description of the R7WebsSecurityHandler authentication bypass.
• Tenda Product Page (AC9): http://www.tenda.com.cn/product/AC9.html — Vendor page for affected hardware; monitor for any future firmware bulletins.
• MITRE CWE-287: https://cwe.mitre.org/data/definitions/287.html — Weakness class reference for improper authentication.
• MITRE ATT&CK T1190: https://attack.mitre.org/techniques/T1190/ — Exploitation of public-facing application technique.
• CISA Known Exploited Vulnerability Catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog — No KEV listing currently; re-check periodically as exploit is confirmed published.

No threat-actor campaigns or exploit-in-the-wild evidence beyond the confirmed published exploit are documented in the provided intelligence data.