CVE-2023-22916
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 · uneditedThe configuration parser of Zyxel ATP series firmware versions 5.10 through 5.35, USG FLEX series firmware versions 5.00 through 5.35, USG FLEX 50(W) firmware versions 5.10 through 5.35, USG20(W)-VPN firmware versions 5.10 through 5.35, and VPN series firmware versions 5.00 through 5.35, which fails to properly sanitize user input. A remote unauthenticated attacker could leverage the vulnerability to modify device configuration data, resulting in DoS conditions on an affected device if the attacker could trick an authorized administrator to switch the management mode to the cloud mode.
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 confidenceA configuration parser in Zyxel ATP, USG FLEX, USG20(W)-VPN, and VPN series firewall firmware versions 5.10-5.35 fails to properly sanitize user input. A remote unauthenticated attacker can modify device configuration data by exploiting this input validation flaw, potentially causing denial of service conditions on the affected device.
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>= 5.00, <= 5.35>= 5.00, <= 5.35>= 5.00, <= 5.35>= 5.00, <= 5.35>= 5.10, <= 5.35>= 5.00, <= 5.35>= 5.00, <= 5.35>= 5.00, <= 5.35CVSS 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
- Required
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/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 device modelAccess the device web interface and navigate to Maintenance > FW Upgrade, or run 'show system-info' via CLI to confirm the model name matches one of: ATP, USG FLEX, USG20(W)-VPN, or VPN seriesAffected if Device model is any of the affected series listed in the CVE
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Check installed firmware versionIn the device web interface go to Maintenance > FW Upgrade to view the current firmware version, or use CLI command 'show system-info' or 'version' to display the running firmware versionAffected if Firmware version falls within 5.00 to 5.35 (or 5.10 to 5.35 for USG Flex 50w)
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Verify management interface exposureCheck router/fouter configuration and public IP exposure for the device's management ports (HTTP/HTTPS typically ports 80/443, or 443/8443). Use external port scanning from an untrusted network to confirm if management interfaces are reachable from the internetAffected if The device management interface is directly accessible from untrusted networks without VPN or IP restriction
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Check for configuration anomaliesReview the device configuration via Backup/Export function in the web interface, or run 'show configuration' via CLI. Look for unexpected changes in system settings, particularly in sections related to management access, user accounts, or network configuration that may indicate exploitationAffected if Configuration file shows unauthorized changes or unexpected entries in management-related settings
The environment is affected if the device is a Zyxel ATP, USG FLEX, USG20(W)-VPN, or VPN series model running firmware between versions 5.00 and 5.35, and the management interface is exposed to untrusted networks.
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.
dbcve · scopedApply vendor-released firmware patches to address the input sanitization vulnerability; until patches are available, limit exposure by restricting management interface access and carefully scrutinizing any management mode change requests.
Firmware version 5.36 or later for USG FLEX series (100, 100w, 200, 50, 50w, 500, 700) and VPN100
- 1. Identify the specific USG FLEX or VPN device model from the affected product list.
- 2. Visit the official Zyxel support website (www.zyxel.com) and navigate to the firmware download section for your specific device model.
- 3. Check for firmware version 5.36 or later, which should contain the security fix for CVE-2023-22916.
- 4. Download the appropriate firmware file for your device model.
- 5. Review the firmware upgrade instructions in the Zyxel product manual or release notes.
- 6. Upload and install the new firmware through the device's web management interface or CLI, following the manufacturer's recommended upgrade procedure.
- 7. After upgrade, verify the device is functioning correctly and confirm the firmware version has been updated.
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation4.0 h
- Implementation8.0 h
- Testing6.0 h
- Review / QA4.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2023-22916 — 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-2023-22916 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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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.
- 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