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Dnr 202l FirmwareOperating system · Dlink

CVE-2026-4205

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 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 impacted element is the function cgi_refresh_db/FTP_Server_BlockIP_Add/FTP_Server_BlockIP_Del of the file /cgi-bin/app_mgr.cgi. Such manipulation leads to command injection. The attack can be executed 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 · moderate confidence

Multiple D-Link NAS devices (DNS-xxx and DNR-xxx series) contain a command injection vulnerability in the /cgi-bin/app_mgr.cgi binary. The functions cgi_refresh_db, FTP_Server_BlockIP_Add, and FTP_Server_BlockIP_Del fail to properly sanitize input, allowing remote attackers to execute arbitrary OS commands.

MitigationThese are end-of-life devices with no vendor patches available. Implement network segmentation to isolate affected devices behind a firewall, or replace the devices with supported hardware.

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 model
    Check the device label, web interface header, or SNMP sysDescr to confirm the exact model number (Dnr 202l, Dnr 326, Dns 1100 4, Dns 120, Dns 1200 05, Dns 1550 04, Dns 315l, or Dns 320)
    Affected if The device model matches any of the eight affected models listed in the CVE
  2. Check the installed firmware version
    Log into the web interface and navigate to System > Firmware Upgrade, or use SSH to run 'cat /etc/fw_version' or 'version' command to retrieve the firmware build date
    Affected if The firmware version date is 2026-02-05 or earlier, matching the <= 2026-02-05 condition in the affected versions
  3. Verify the web CGI interface is accessible
    Attempt to access https://[device-ip]/cgi-bin/app_mgr.cgi or check if the URL returns a valid response rather than a 404 error
    Affected if The /cgi-bin/app_mgr.cgi endpoint is reachable from the network being tested
  4. Confirm the device is network-exposed
    Review firewall rules, NAT configurations, or ACLs to determine if the web management port (typically 80/443) is accessible from untrusted networks
    Affected if The device web interface is exposed to the internet or untrusted LAN segments rather than being isolated
  5. Check for signs of exploitation
    Review web server access logs for requests to /cgi-bin/app_mgr.cgi with unusual parameters (look for shell metacharacters like ; | ` $ in cgi_refresh_db, FTP_Server_BlockIP_Add, or FTP_Server_BlockIP_Del function calls)
    Affected if Log analysis reveals suspicious requests containing command injection patterns to the vulnerable CGI functions

You are affected if you run any of the eight listed D-Link NAS models with firmware dated 2026-02-05 or earlier and the web 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

These are end-of-life devices with no vendor patches available. Implement network segmentation to isolate affected devices behind a firewall, or replace the devices with supported hardware.

Fix this in Dnr 202l Firmware Scoped from the published advisory
  • Consultation6.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA2.0 h
22.0 hours of engineering $3,900
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An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $6,240.

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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-2026-4205 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