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Rt Ax86u FirmwareOperating system · Asus

CVE-2020-36109

CRITICAL · 9.8 CVSS v3.1 Published 2021-02-01
Fix available
A fix is available. Upgrade to 9.0.0.4_386 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
ASUS RT-AX86U router firmware below version under 9.0.0.4_386 has a buffer overflow in the blocking_request.cgi function of the httpd module that can cause code execution when an attacker constructs malicious data.

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 vulnerability in the httpd module's blocking_request.cgi function of ASUS RT-AX86U routers running firmware versions prior to 9.0.0.4_386. The flaw allows remote attackers to execute arbitrary code via crafted HTTP requests to the web interface.

MitigationUpdate ASUS RT-AX86U firmware to version 9.0.0.4_386 or later. As a compensating control, restrict access to the router's web management interface to trusted networks or VPN.

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
Rt Ax86u FirmwareOperating system
Affected:< 9.0.0.4_386

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. Confirm device model is ASUS RT-AX86U
    Access router administration panel or check device label/marketing materials for model number
    Affected if Device is not an ASUS RT-AX86U model - other models are not affected by this specific CVE
  2. Check installed firmware version
    Log into router web UI (typically at 192.168.1.1) and navigate to Administration > Firmware Upgrade, or use 'nvram get firmver' via telnet/SSH if enabled
    Affected if Unable to retrieve firmware version - cannot determine vulnerability status
  3. Compare firmware version against vulnerable threshold
    Compare installed firmware version string to 9.0.0.4_386 - versions numerically less than this (e.g., 9.0.0.4_384, 9.0.0.3_xxx) are affected
    Affected if Installed firmware version is less than 9.0.0.4_386 - router is vulnerable if other conditions met
  4. Verify httpd web interface is accessible
    Attempt HTTP/HTTPS access to router LAN IP (default 192.168.1.1) from internal network
    Affected if Web interface is disabled or inaccessible - attack surface may be reduced but firmware may still be vulnerable
  5. Confirm blocking_request.cgi endpoint exists
    Send a GET or POST request to http://[router-ip]/blocking_request.cgi and observe response (may return error or require authentication)
    Affected if Endpoint returns any response (even error) - the vulnerable function exists in the firmware

Router is affected if it is an ASUS RT-AX86U model running firmware version below 9.0.0.4_386 with the httpd web interface accessible and the blocking_request.cgi endpoint present.

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 9.0.0.4_386 or later
Fixed in 9.0.0.4_386
Interim mitigation

Update ASUS RT-AX86U firmware to version 9.0.0.4_386 or later. As a compensating control, restrict access to the router's web management interface to trusted networks or VPN.

Recommended fix High confidence

ASUS RT-AX86U firmware version 9.0.0.4_386 or later

  1. Access the ASUS RT-AX86U router web interface by navigating to the router's IP address (typically 192.168.1.1) in a web browser
  2. Log in with administrator credentials
  3. Navigate to the firmware update section (usually under Administration > Firmware Upgrade or System > Firmware Upgrade)
  4. Check the current firmware version displayed on the page
  5. If the current version is below 9.0.0.4_386, download the latest firmware version 9.0.0.4_386 or higher from the official ASUS support website (www.asus.com)
  6. In the firmware upgrade page, click 'Upload' or 'Choose File' and select the downloaded firmware file
  7. Click 'Upload' to begin the firmware update process - do not power off the router during the update
  8. Wait for the update to complete and the router to reboot automatically
Caveat Review ASUS release notes for the update; backup router configuration before upgrading as a precaution

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

Fix this in Rt Ax86u Firmware Scoped from the published advisory
  • Consultation6.0 h
  • Implementation4.0 h
  • Testing6.0 h
  • Review / QA4.0 h
20.0 hours of engineering $3,540
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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-2020-36109 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