CVE-2023-39238
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. This vulnerability is caused by lacking validation for a specific value within its set_iperf3_svr.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 · moderate confidenceFormat string vulnerability in the set_iperf3_svr.cgi module of ASUS RT-AX56U V2 router firmware caused by insufficient validation of a specific input parameter. An authenticated remote attacker with administrator privileges can exploit this to achieve arbitrary code execution, system command execution, or cause denial of service.
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 modelLog into the router administrative interface and check the device model under System > Device Info, or look at the physical device label. Common affected models are RT-AX55, RT-AX56U V2, and RT-AC86U.Affected if The router model is RT-AX55, RT-AX56U V2, or RT-AC86U.
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Check installed firmware versionIn the router web interface, navigate to System > Firmware Version or Administration > Firmware Upgrade to view the current firmware build number.Affected if The firmware version is exactly 3.0.0.4.386_50460 (for RT-AX55 or RT-AX56U V2) or 3.0.0.4_386_51529 (for RT-AC86U).
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Verify web interface accessibilityCheck if the router administrative web interface (port 80/443) is exposed to the internet or untrusted networks via WAN access settings under Administration > System > Remote Access Configuration.Affected if Remote web management is enabled and accessible from WAN, increasing exposure to unauthenticated attack attempts.
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Check for unauthorized administrator sessionsReview the router logs under System Log > Connections for suspicious admin login events from unexpected IP addresses, or check Active Clients for unknown devices with admin privileges.Affected if There are administrative login attempts or sessions from unrecognized IP addresses.
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Inspect for unexpected processes or configuration changesIf you have shell access (via telnet/SSH), run 'ps' to list running processes and check /etc/config/ for any unexpected modifications to CGI script configurations.Affected if Unexpected processes are running or configuration files related to iperf3 have been modified.
The device is affected if it is an RT-AX55, RT-AX56U V2, or RT-AC86U model running the exact firmware version listed and the web administrative interface is accessible to the attacker.
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 from ASUS when released. In the interim, restrict administrative web interface access to trusted internal networks or VPN-only, and monitor for unauthorized administrative access attempts.
- Consultation3.0 h
- Implementation6.0 h
- Testing4.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2023-39238 — 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-2023-39238 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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