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Vigor2620 FirmwareOperating system · Draytek

CVE-2023-31447

CRITICAL · 9.8 CVSS v3.1 Published 2023-08-21
Fix available
A fix is available. Upgrade to 3.9.8.4 or later.
See remediation →
100/100
Remediation priority · Urgent
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
user_login.cgi on Draytek Vigor2620 devices before 3.9.8.4 (and on all versions of Vigor2925 devices) allows attackers to send a crafted payload to modify the content of the code segment, insert shellcode, and execute arbitrary code.

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

Buffer overflow or code injection vulnerability in user_login.cgi on Draytek Vigor2620 (before firmware 3.9.8.4) and all Vigor2925 versions allows remote attackers to inject shellcode into the code segment and achieve arbitrary code execution via crafted HTTP requests.

MitigationApply vendor firmware updates: upgrade Vigor2620 to version 3.9.8.4 or later; for Vigor2925, contact Draytek for available patches since all versions are affected.

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
Vigor2620 FirmwareOperating system
Affected:< 3.9.8.4
Vigor2625 FirmwareOperating system
Affected:all versions

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 Draytek router model
    Access the router web interface and locate the model name on the login page or system status page, or check the physical device label
    Affected if The model is Vigor2620, Vigor2625, or Vigor2925
  2. Determine the installed firmware version
    Log into the router web interface and navigate to System Maintenance > Firmware Upgrade (or similar status page) to view the current firmware version, or use the CLI command 'sys df' or 'version' if SSH/Telnet is enabled
    Affected if Unable to determine the firmware version (model may still be affected)
  3. Compare firmware version against affected ranges
    For Vigor2620: note that versions below 3.9.8.4 are affected; for Vigor2625 and Vigor2925: all versions are affected regardless of version number
    Affected if Vigor2620 with firmware version less than 3.9.8.4, OR any Vigor2625 version, OR any Vigor2925 version
  4. Confirm user_login.cgi is accessible
    Attempt to access the URI '/cgi-bin/user_login.cgi' on the router's web server (e.g., http://<router-ip>/cgi-bin/user_login.cgi)
    Affected if The endpoint returns a response (indicates the vulnerable CGI is present)

If the device is a Vigor2620 with firmware below 3.9.8.4, or any Vigor2625/Vigor2925 model, and the user_login.cgi endpoint is accessible, the environment is affected by this 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.

dbcve · scoped
Upgrade available Upgrade to 3.9.8.4 or later
Fixed in 3.9.8.4
Interim mitigation

Apply vendor firmware updates: upgrade Vigor2620 to version 3.9.8.4 or later; for Vigor2925, contact Draytek for available patches since all versions are affected.

Recommended fix Moderate confidence

Draytek Vigor2620 Firmware 3.9.8.4 or later

  1. Obtain the firmware version 3.9.8.4 or later for the Draytek Vigor2620 from the official Draytek website (draytek.com)
  2. Access the Vigor2620 web management interface
  3. Navigate to the firmware upgrade section (typically under System Maintenance > Firmware Upgrade)
  4. Upload the downloaded firmware file (3.9.8.4 or later)
  5. Wait for the firmware upload and installation to complete - do not power off the device during this process
  6. After reboot, verify the firmware version has been updated successfully
  7. For Vigor2625 (or Vigor2925 if that was intended): Contact Draytek support for available firmware updates since all versions are affected
Caveat Standard firmware upgrade risks apply - ensure backup of configuration; power interruption during upgrade can brick device

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Vigor2620 Firmware Scoped from the published advisory
  • Consultation6.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA3.0 h
21.0 hours of engineering $3,780
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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-2023-31447 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