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Dnr 202l FirmwareOperating system · Dlink

CVE-2026-4213

CRITICAL · 9.8 CVSS v3.1 Published 2026-03-16
Fix available
A fix is available. Upgrade to after 2026-02-05 or later.
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 was detected in D-Link DNS-120, DNR-202L, DNS-315L, DNS-320, DNS-320L, DNS-320LW, DNS-321, DNR-322L, DNS-323, DNS-325, DNS-326, DNS-327L, DNR-326, DNS-340L, DNS-343, DNS-345, DNS-726-4, DNS-1100-4, DNS-1200-05 and DNS-1550-04 up to 20260205. This vulnerability affects the function cgi_myfavorite_del_user/cgi_myfavorite_verify of the file /cgi-bin/gui_mgr.cgi. Performing a manipulation results in stack-based buffer overflow. The attack may be initiated remotely. The exploit is now 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

A stack-based buffer overflow vulnerability exists in the CGI binary gui_mgr.cgi on multiple D-Link NAS devices. The overflow occurs in the cgi_myfavorite_del_user and cgi_myfavorite_verify functions via unsanitized user input, allowing remote attackers to potentially execute arbitrary code with elevated privileges through specially crafted HTTP requests.

MitigationRestrict network access to affected devices, disable the vulnerable CGI endpoint if possible, or replace end-of-life devices as vendor firmware updates may not be available.

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
Dnr 202l FirmwareOperating system
Affected:<= 2026-02-05
Dnr 326 FirmwareOperating system
Affected:<= 2026-02-05
Dns 1100 4 FirmwareOperating system
Affected:<= 2026-02-05
Dns 120 FirmwareOperating system
Affected:<= 2026-02-05
Dns 1200 05 FirmwareOperating system
Affected:<= 2026-02-05
Dns 1550 04 FirmwareOperating system
Affected:<= 2026-02-05
Dns 315l FirmwareOperating system
Affected:<= 2026-02-05
Dns 320 FirmwareOperating system
Affected:<= 2026-02-05

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 the D-Link NAS device model
    Access the device web interface or check the device label to determine the exact model (e.g., DNR-202L, DNR-326, DNS-1100, DNS-320, etc.)
    Affected if The model matches any of the following: Dnr 202l, Dnr 326, Dns 1100 4, Dns 120, Dns 1200 05, Dns 1550 04, Dns 315l, or Dns 320
  2. Check the installed firmware version
    Log into the device web interface, navigate to the System or Settings section, and locate the firmware version information. Alternatively, check the firmware file name or the update history.
    Affected if The firmware version date is on or before 2026-02-05 (the firmware file date or version string indicates an older build)
  3. Verify if the CGI web interface is enabled and accessible
    Attempt to access the gui_mgr.cgi endpoint by browsing to http://[device-ip]/cgi/gui_mgr.cgi or similar path. Check if the device responds to CGI requests.
    Affected if The device web interface is accessible and the CGI binary responds to HTTP requests
  4. Confirm network exposure of the management interface
    Determine if the device HTTP/HTTPS ports (typically 80/443) are accessible from untrusted networks by reviewing firewall rules, port forwarding configurations, or performing a port scan from an external location.
    Affected if The device management interface is exposed to the internet or untrusted LAN segments without proper access controls
  5. Review web server access logs for suspicious requests
    If accessible, examine the device or upstream proxy logs for requests to /cgi/gui_mgr.cgi with unusually long parameters, especially those targeting functions like myfavorite_del_user or myfavorite_verify.
    Affected if Log entries show requests to gui_mgr.cgi with abnormally long parameter strings or patterns indicative of buffer overflow testing

A user is affected if they are running any of the listed D-Link NAS models with firmware dated 2026-02-05 or earlier, and the device CGI interface 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
Upgrade available Upgrade to a release after 2026-02-05
Interim mitigation

Restrict network access to affected devices, disable the vulnerable CGI endpoint if possible, or replace end-of-life devices as vendor firmware updates may not be available.

Fix this in Dnr 202l 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-2026-4213 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data