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Dnr 202l FirmwareOperating system · Dlink

CVE-2026-4204

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 flaw has been found 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. The affected element is the function cgi_myfavorite_add/cgi_myfavorite_set/cgi_myfavorite_del/cgi_myfavorite_set_sort_info/cgi_myfavorite_remove_apkg/cgi_myfavorite_compare_apkg/cgi_mycloud_auto_downlaod of the file /cgi-bin/gui_mgr.cgi. This manipulation of the argument f_user causes command injection. Remote exploitation of the attack is possible. The exploit has been published 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

Command injection vulnerability in D-Link NAS devices (multiple models including DNS-320, DNS-325, DNS-340L, etc.). The cgi_mgr.cgi file contains multiple functions (cgi_myfavorite_add, cgi_myfavorite_set, cgi_myfavorite_del, etc.) that accept user input via the f_user parameter without proper sanitization, allowing arbitrary OS command execution. This is a pre-authentication remote vulnerability with CVSS 9.8.

MitigationThese are legacy/EOL devices with no active vendor support. Apply network segmentation to isolate NAS devices from untrusted networks, block external access to the /cgi-bin/ interface via firewall, or consider decommissioning/replacing affected devices if patches are unavailable.

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 D-Link NAS model
    Access the device web interface or check the device label to confirm the exact model number (e.g., DNS-320, DNS-325, DNS-340L, DNR-202L, DNR-326, DNS-1100-4, DNS-120, DNS-1200-05, DNS-1550-04, DNS-315L). Compare against the list of affected models.
    Affected if The device model matches one of the listed affected products.
  2. Check firmware version
    In the device web interface, navigate to System > Firmware Upgrade or Status page to view the installed firmware version. The affected version is anything dated 2026-02-05 or earlier.
    Affected if The installed firmware version is <= 2026-02-05.
  3. Verify cgi_mgr.cgi is accessible
    Attempt to access the URL pattern /cgi-bin/cgi_mgr.cgi on the device (e.g., http://[device-ip]/cgi-bin/cgi_mgr.cgi). The vulnerability exists in the cgi_myfavorite_add, cgi_myfavorite_set, and cgi_myfavorite_del functions.
    Affected if The CGI endpoint responds, indicating the vulnerable binary is present on the device.
  4. Assess network exposure
    Check if the device web interface (port 80/443) or /cgi-bin/ directory is accessible from external/untrusted networks. Review firewall rules and router port forwarding configurations.
    Affected if The device CGI interface is reachable from untrusted networks without firewall blocks.

If the device is an affected D-Link NAS model running firmware dated 2026-02-05 or earlier and the cgi_mgr.cgi interface is network-accessible, the environment is likely affected by this command injection vulnerability.

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

These are legacy/EOL devices with no active vendor support. Apply network segmentation to isolate NAS devices from untrusted networks, block external access to the /cgi-bin/ interface via firewall, or consider decommissioning/replacing affected devices if patches are unavailable.

Fix this in Dnr 202l Firmware Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing3.0 h
  • Review / QA2.0 h
17.0 hours of engineering $3,050
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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-2026-4204 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