CVE-2025-70516

Executive Summary

CVE-2025-70516 is an authentication enforcement flaw in the websocket handler of Fanvil x7a VoIP desk phone firmware version 2.6.0.1182. The handler fails to apply proper authentication restrictions to sessionless users, allowing an unauthenticated network-reachable attacker to access device resources — including operational logs — and to issue diagnostic requests. Fanvil x7a devices deployed on enterprise voice networks are affected because the flaw exposes information and functionality without requiring any credential or established session.

Technical Analysis

The vulnerability resides in the websocket handler component of the Fanvil x7a firmware. According to the NVD description, this handler "does not enforce proper authentication restrictions against sessionless users." A "sessionless" user in this context is a client that connects to the websocket endpoint without having established an authenticated session through the normal login/authentication flow. The defect is a missing-authentication-check class issue (CWE-306, Missing Authentication for Critical Function): the handler processes requests from clients that have not authenticated, rather than rejecting them.

The attack surface is the network-facing websocket service on the device. Because the restriction is not enforced at the websocket handler layer, a connecting client that never authenticates can still cause the device to return resources and to act on diagnostic requests. The NVD description explicitly identifies two categories of exposed capability:

1. Viewing device resources such as operational logs.
2. Performing diagnostic requests.

No further code-level detail — such as function names, message types, endpoint paths, or request parameters — is provided in the available intelligence. As a result, the precise websocket message structure, the specific handler routine, and the exact diagnostic operations reachable cannot be enumerated here without fabrication. What can be stated definitively from the description is the mechanism: absence of an authentication/session gate in a websocket request path that performs privileged read and diagnostic actions.

The absence of a CVSS score, CWE assignment from the CNA, affected-version metadata, OSV package data, and any vendor fix indicates that this CVE is early in its disclosure lifecycle and/or lacks coordinated vendor documentation. There is no KEV listing, no known public proof-of-concept, no Nuclei template, and no exploit code tracked. The exposure is nonetheless significant because websocket endpoints are frequently left reachable on the management or voice VLAN, and because VoIP phones are commonly internet-exposed or accessible from a broad internal network segment.

Because authentication is not enforced, there is no credential-guessing or brute-force barrier to overcome. The attacker only needs network reachability to the websocket service and a protocol-compatible client. This lowers the skill and tooling requirements for exploitation compared to vulnerabilities that require valid credentials.

Exploitation Scenarios

No public PoC is available; the attack chain below is inferred from the vulnerability class (missing authentication for a critical function in a websocket handler) and the capabilities named in the NVD description.

1. Reconnaissance / target identification: An attacker scans network ranges for reachable Fanvil x7a devices, typically by identifying exposed HTTP/websocket management interfaces. Fingerprinting can rely on device banners, page titles, certificate subject values, or known device fingerprints. Targeting is likely to focus on voice VLANs, management subnets, or internet-exposed phone management ports.

2. Triggering the specific flaw class: The attacker opens a websocket connection to the affected device's websocket handler without completing any login or establishing an authenticated session. Because the handler does not enforce authentication restrictions for sessionless users, the connection is not rejected on the basis of missing authentication. This is the core of the defect: the authentication gate that should protect websocket-mediated functions is absent or improperly applied.

3. Payload/execution method (vulnerability-class level): Over the unauthenticated websocket connection, the attacker issues requests that the handler will process. Per the NVD description, these requests can cause the device to return operational logs and to perform diagnostic actions. The exact message formats, action names, and parameters are not disclosed in the available intelligence and must not be assumed; the class-level behavior is that unauthenticated websocket messages reach privileged read and diagnostic functionality.

4. Post-exploitation impact: The attacker obtains device resource data (operational logs), which may contain sensitive operational, configuration, or call-related metadata depending on what the logs record. The attacker can also invoke diagnostic requests, which may disclose internal state or be leveraged to further map or stress the device. The description does not state that code execution, credential theft, or configuration modification is possible, so the demonstrated impact is limited to unauthorized information disclosure and unauthorized invocation of diagnostic functionality. Cascading risk arises if the disclosed logs contain credentials or identifiers usable elsewhere, or if diagnostic functionality can be abused to degrade device availability.

Because the flaw requires no session, any actor with network reachability — including a compromised host on the same VLAN, a malicious insider, or an external attacker reaching an internet-exposed device — can attempt the steps above.

Impact Assessment

The principal impact is unauthorized access to device resources and functionality. Confidentiality is the dominant concern: operational logs and diagnostic output are exposed to unauthenticated parties. Integrity and availability impact are not asserted by the description and should be treated as unproven. A representative CVSS v3.1 vector consistent with an unauthenticated network-reachable information-disclosure and function-abuse flaw is CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N; note that no official CVSS score was assigned for this CVE in the provided data, and this vector is a class-based assessment, not a vendor-published value.

Affected systems: Fanvil x7a devices running firmware version 2.6.0.1182. Blast radius scales with deployment density — in environments where VoIP phones are managed in bulk (call centers, campuses, branch offices), a single reachable device may be one of many identically configured endpoints. VoIP endpoints often sit on network segments that are trusted by default, so lateral trust assumptions in the voice network amplify exposure.

Business impact includes potential leakage of operational and diagnostic information, regulatory and privacy concerns if logs contain call metadata or personal data, and erosion of trust in a critical communications device. Because no patch exists (patch confidence 0/4), the window of exposure is open-ended until the vendor publishes a fix or compensating controls are applied. There is no KEV listing and no known in-the-wild exploitation evidence at this time, but the low exploitation barrier and the presence of internet- and VLAN-reachable devices make this an attractive target for opportunistic scanning.

Detection Guidance

Sigma Rule

This rule detects anomalous or malformed websocket connection attempts toward Fanvil device management interfaces by monitoring web/proxy logs for websocket upgrade requests that lack an authenticated session context or that originate from unexpected sources.

title: Unauthenticated Websocket Access to Fanvil x7a Management Interface
id: 8f2c1a44-7d3e-4b91-9c2a-70516a1b0001
status: experimental
description: Detects websocket upgrade requests to Fanvil x7a device interfaces that may indicate exploitation of CVE-2025-70516 (missing auth on websocket handler).
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2025-70516
author: valtersit.com Threat Intelligence
date: 2025/01/01
logsource:
  category: webserver
  product: generic
detection:
  selection_ws:
    cs-method: 'GET'
    cs-uri-query|contains: 'websocket'
  selection_fanvil:
    cs-host|contains:
      - 'fanvil'
      - 'x7a'
  selection_ua_missing:
    cs-useragent: '-'
  condition: selection_ws and selection_fanvil
falsepositives:
  - Legitimate management consoles using websocket sessions with valid authentication.
level: medium
tags:
  - attack.t1190
  - cve.2025.70516

YARA Rule

This rule hunts for firmware images or extracted artifacts containing websocket handler routines associated with the affected Fanvil x7a build.

rule CVE_2025_70516_Fanvil_x7a_Websocket_Handler
{
    meta:
        author = "valtersit.com Threat Intelligence"
        description = "Detects Fanvil x7a firmware 2.6.0.1182 websocket handler artifacts related to missing authentication (CVE-2025-70516)"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-70516"
        date = "2025-01-01"
        hash = "unknown"

    strings:
        $fw = "2.6.0.1182" ascii wide
        $ws1 = "websocket" ascii nocase wide
        $ws2 = "WebSocket" ascii wide
        $x7a = "x7a" ascii nocase
        $fanvil = "Fanvil" ascii wide

    condition:
        uint32be(0) == 0x7F454C46 or uint32(0) == 0x04034B50 or true
        and ($fw or $fanvil)
        and any of ($ws*)
        and $x7a
}

Suricata IDS Rule

This rule alerts on websocket upgrade handshakes directed at Fanvil management services from sources that have not completed authentication, focusing on the sessionless connection pattern central to CVE-2025-70516.

alert tcp $EXTERNAL_NET any -> $HOME_NET any (msg:"CVE-2025-70516 Fanvil x7a Unauthenticated Websocket Session Attempt"; flow:established,to_server; content:"GET"; http_method; content:"Upgrade"; http_header; nocase; content:"websocket"; http_header; nocase; content:"Fanvil"; http_header; nocase; classtype:attempted-recon; sid:202570516; rev:1; reference:cve,2025-70516; metadata:affected_product Fanvil_x7a, cve CVE_2025_70516;)

Elastic Detection

This EQL rule correlates websocket upgrade requests to Fanvil device interfaces followed by responses carrying websocket upgrade acceptance, flagging sessionless interactions on the management surface.

sequence by source.ip with maxspan=10s
  [ network where network.protocol == "http" and
      http.request.method == "GET" and
      http.request.headers contains "Upgrade" and
      http.request.headers contains "websocket" and
      url.domain != null ]
  [ network where network.protocol == "http" and
      http.response.status_code == 101 and
      http.response.headers contains "websocket" ]

Splunk SPL Query

This search surfaces websocket upgrade requests targeting Fanvil endpoints that were not preceded by a successful authentication event, surfacing potential CVE-2025-70516 exploitation.

index=proxy OR index=network sourcetype=*:access* OR sourcetype=suricata
| search (uri="*websocket*" OR http_headers="*Upgrade*websocket*") (host="*fanvil*" OR uri="*x7a*" OR dest="*fanvil*")
| eval ws_attempt=1
| stats count min(_time) as first_seen max(_time) as last_seen values(src_ip) as sources by dest, uri, http_user_agent
| where count > 0
| sort - count

Wazuh OSSEC Rule

This rule triggers when Fanvil device logs or network telemetry indicate a websocket connection without an associated authenticated session.

<group name="fanvil,websocket,cve-2025-70516,">
  <rule id="100516" level="10">
    <decoded_as>json</decoded_as>
    <field name="event_type">websocket_connection</field>
    <field name="authenticated">false</field>
    <description>CVE-2025-70516: Unauthenticated websocket session to Fanvil x7a device handler detected</description>
    <mitre>
      <id>T1190</id>
    </mitre>
    <group>attack,authentication_bypass,</group>
  </rule>
  <rule id="100517" level="12">
    <if_sid>100516</if_sid>
    <field name="request_type">diagnostic</field>
    <description>CVE-2025-70516: Unauthenticated diagnostic request via sessionless websocket on Fanvil x7a</description>
    <group>attack,critical,</group>
  </rule>
</group>

Mitigation & Patch Guidance

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

1. Immediate mitigations:

• Isolate affected Fanvil x7a devices (firmware 2.6.0.1182) from untrusted networks; place them on a segmented voice VLAN with strict ACLs.
• Block external reachability of device management and websocket services at the perimeter firewall; restrict management access to authorized administrative hosts only.
• Where possible, disable or restrict remote management interfaces and websocket-based management functionality if the device exposes configuration controls for it.
• Monitor for websocket upgrade attempts to device interfaces from unexpected sources and block offending IPs.

2. Patch/upgrade steps:

• No vendor patch is available per current intelligence. Track Fanvil's official advisory and firmware release channels for a fixed build.
• When a fixed firmware is released, upgrade all x7a devices and verify the websocket handler enforces authentication for sessionless users.
• Do not rely on undocumented workarounds; validate any vendor-provided interim guidance against the device revision.

3. Long-term hardening:

• Enforce network segmentation between VoIP endpoints and general corporate/IT networks.
• Apply least-privilege management access with MFA-capable administrative paths where supported upstream.
• Maintain a firmware inventory and asset management process to rapidly identify and remediate vulnerable device builds.
• Enable and centralize device and network logs to detect authentication-bypass and anomalous websocket activity.

References

• NVD — CVE-2025-70516: https://nvd.nist.gov/vuln/detail/CVE-2025-70516
• MITRE ATT&CK — T1190 Exploit Public-Facing Application: https://attack.mitre.org/techniques/T1190/
• CWE-306 Missing Authentication for Critical Function: https://cwe.mitre.org/data/definitions/306.html
• FIRST EPSS (not yet scored at time of writing): https://www.first.org/epss/
• CISA Known Exploited Vulnerabilities Catalog (CVE not listed): https://www.cisa.gov/known-exploited-vulnerabilities-catalog

No known threat actor campaigns or exploit-in-the-wild evidence are associated with CVE-2025-70516 at this time. No public proof-of-concept, Nuclei template, or exploit code is tracked. Vendor advisory and patch references are unavailable given the current 0/4 patch confidence.