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A3300r FirmwareOperating system · Totolink

CVE-2025-12239

CRITICAL · 9.8 CVSS v3.1 Published 2025-10-27
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 weakness has been identified in TOTOLINK A3300R 17.0.0cu.557_B20221024. The impacted element is the function setDdnsCfg of the file /cgi-bin/cstecgi.cgi. Executing manipulation can lead to buffer overflow. The attack may be performed from remote. The exploit has been made available to the public and could be exploited.

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 · moderate confidence

A buffer overflow vulnerability exists in the setDdnsCfg function of the TOTOLINK A3300R router's web interface CGI binary (cstecgi.cgi). Remote attackers can exploit this by sending specially crafted DDNS configuration parameters to overflow a buffer and potentially execute arbitrary code. The vulnerability is exploitable without authentication given the CVSS 9.8 rating.

MitigationUpdate the router firmware to a patched version if available from TOTOLINK; otherwise, disable the DDNS feature and restrict access to the router's web administration interface to trusted IPs only.

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
A3300r FirmwareOperating system
Affected:= 17.0.0cu.557_b20221024

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 router model
    Access the router web interface or check the device label to confirm the model is Totolink A3300R
    Affected if Router model is not Totolink A3300R - different models may have different vulnerabilities
  2. Check installed firmware version
    Log into the router web interface and navigate to System Status or Firmware Upgrade page to view the current firmware version. Alternatively, inspect the firmware file if accessible via backup or extraction.
    Affected if Firmware version matches exactly 17.0.0cu.557_B20221024 - this is the only affected version listed
  3. Verify CGI binary presence
    Check if the file /cgi-bin/cstecgi.cgi exists on the router by attempting to access it via HTTP/HTTPS (e.g., http://<router_ip>/cgi-bin/cstecgi.cgi)
    Affected if The CGI binary is present and responds to requests - the vulnerability resides in this binary
  4. Confirm DDNS feature is accessible
    Navigate to the router web interface DDNS configuration page (usually under Network or Advanced settings) to confirm the DDNS function setDdnsCfg is exposed and accessible to authenticated users
    Affected if DDNS configuration interface is present and accessible - the buffer overflow occurs in the setDdnsCfg function handling DDNS input
  5. Assess web interface accessibility
    Determine if the router web interface (port 80/443) is exposed to untrusted networks or the internet by checking router firewall rules and port forwarding configurations
    Affected if The CGI endpoint is reachable from an untrusted network - remote attackers need access to the web interface to trigger the buffer overflow

You are affected only if you have a Totolink A3300R router running firmware version 17.0.0cu.557_B20221024 with the CGI binary accessible and DDNS feature enabled.

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

Update the router firmware to a patched version if available from TOTOLINK; otherwise, disable the DDNS feature and restrict access to the router's web administration interface to trusted IPs only.

Fix this in A3300r Firmware Scoped from the published advisory
  • Consultation4.0 h
  • Implementation2.0 h
  • Testing3.0 h
  • Review / QA2.0 h
11.0 hours of engineering $1,970
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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-2025-12239 in production — separate from our analysis above.

No notes yet

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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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