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T6 FirmwareOperating system · Totolink

CVE-2025-7862

CRITICAL · 9.8 CVSS v3.1 Published 2025-07-20
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
100/100
Remediation priority · Urgent
Public exploit Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
A vulnerability has been found in TOTOLINK T6 4.1.5cu.748_B20211015 and classified as critical. Affected by this vulnerability is the function setTelnetCfg of the file /cgi-bin/cstecgi.cgi of the component Telnet Service. The manipulation of the argument telnet_enabled with the input 1 leads to missing authentication. The attack can be launched remotely. The exploit has been disclosed to the public and may be used.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

TOTOLINK T6 router firmware 4.1.5cu.748_B20211015 contains an authentication bypass vulnerability in the setTelnetCfg function of the cstecgi.cgi web interface. By sending a crafted request with telnet_enabled=1, an unauthenticated remote attacker can enable the Telnet service, gaining remote command execution capability on the device.

MitigationApply vendor firmware update when available; until then, block external access to Telnet ports (23/TCP) via perimeter firewall and segment affected devices from sensitive network zones.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
T6 FirmwareOperating system
Affected:= v4.1.5cu.748_b20211015

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify device model and firmware version
    Access the router's web administration interface or check the device label/menu for the exact model (T6) and firmware version string (v4.1.5cu.748_b20211015)
    Affected if The device is a Totolink T6 router running firmware version v4.1.5cu.748_B20211015 exactly
  2. Verify the web management interface is accessible
    Attempt to access the cstecgi.cgi endpoint or the router's standard web interface on the local network (typically HTTP port 80)
    Affected if The cstecgi.cgi web interface is reachable and responds to requests
  3. Check if Telnet service is currently enabled
    Attempt to connect to the device on TCP port 23 (Telnet) from the local network, or check the router's web interface for Telnet service status under the Telnet/remote management settings
    Affected if Telnet service is enabled and accepting connections on port 23/TCP
  4. Determine if the web interface allows unauthenticated Telnet configuration changes
    Send a crafted HTTP POST request to the cstecgi.cgi endpoint with the parameter setTelnetCfg or telnet_enabled=1 without providing authentication credentials
    Affected if The request successfully modifies Telnet settings without authentication
  5. Assess network exposure of Telnet and management interfaces
    Scan the device's WAN/public IP address for open ports 23 (Telnet) and 80/443 (web management), or review firewall rules to determine if these ports are exposed to external networks
    Affected if Port 23/TCP or the web management interface is accessible from WAN/external networks

A user is affected if they are running the specific firmware version v4.1.5cu.748_B20211015 on a Totolink T6 router and the web interface or Telnet service is network-accessible.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply vendor firmware update when available; until then, block external access to Telnet ports (23/TCP) via perimeter firewall and segment affected devices from sensitive network zones.

Fix this in T6 Firmware Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA2.0 h
18.0 hours of engineering $3,200
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2025-7862 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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