CVE-2023-39239
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 · uneditedIt is identified a format string vulnerability in ASUS RT-AX56U V2’s General function API. This vulnerability is caused by lacking validation for a specific value within its apply.cgi module. A remote attacker with administrator privilege can exploit this vulnerability to perform remote arbitrary code execution, arbitrary system operation or disrupt service.
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 confidenceA format string vulnerability exists in the ASUS RT-AX56U V2 router's apply.cgi module within the General function API. The vulnerability stems from insufficient validation of a specific input value, allowing a remote attacker with administrator privileges to inject format string specifiers. This can lead to remote code execution, arbitrary system command execution, or service disruption.
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= 3.0.0.4.386_50460= 3.0.0.4.386_50460= 3.0.0.4_386_51529CVSS 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
- High
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:H/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 checksWork through these to decide whether this CVE applies to you.
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Identify router modelAccess the router web administration interface and navigate to Administration > System, or check the product label on the device. Confirm the model is RT-AX55, RT-AX56U V2, or RT-AC86U.Affected if The device model is RT-AX55, RT-AX56U V2, or RT-AC86U.
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Check firmware versionIn the router web interface, go to Administration > Firmware Upgrade or Advanced > System to view the installed firmware version. Compare against 3.0.0.4.386_50460 for RT-AX55/RT-AX56U V2 or 3.0.0.4_386_51529 for RT-AC86U.Affected if Firmware version equals exactly 3.0.0.4.386_50460 (RT-AX55 or RT-AX56U V2) or 3.0.0.4_386_51529 (RT-AC86U).
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Verify web interface accessibilityAttempt to access the router login page via HTTP/HTTPS at the router IP address (commonly 192.168.1.1). Determine if the apply.cgi endpoint responds to requests.Affected if The router web interface and apply.cgi are reachable from an untrusted network.
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Confirm administrator access requirementReview router access control settings under Administration > System > Remote Access Management. The vulnerability requires administrator-level privileges to exploit.Affected if Remote administrator access is enabled or the web interface is exposed to untrusted networks where unauthorized admin sessions could be established.
You are affected if you run an RT-AX55, RT-AX56U V2, or RT-AC86U on the specific firmware versions listed and the router web interface is accessible to potential attackers.
Generated from the published advisory. Verify against your own configuration.
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 dataApply vendor firmware updates when released; until then, restrict administrative web interface access to trusted networks only and monitor for unauthorized admin session activity.
- Consultation1.0 h
- Implementation2.0 h
- Testing2.0 h
- Review / QA1.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2023-39239 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2023-39239 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- 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
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