CyberSecBulletin
CVE-2023-22916NVD status: Modified

The configuration parser of Zyxel ATP series firmware versions 5.10 through 5.35, USG FLEX…

Published Updated By the CyberSecBulletin desk

CVE-2023-22916 is a high-severity improper input validation vulnerability in ATP series firmware from Zyxel, with a CVSS 3.1 base score of 8.1 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, but only if a user takes part, for example by opening a link or file. Affected ATP series firmware versions: 5.10 through 5.35. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.69% chance of exploitation within 30 days, higher than 53% of scored CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Check which version of ATP series firmware you run against the affected versions below, and install the vendor's latest release.
  2. Read the advisory on zyxel.com for workarounds and exact fixed builds.
  3. Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
  4. Because the attack needs a user to take part, warn users about unexpected links and files related to this product until it is patched.

Affected products and versions

VendorProductAffected versionsFixed in
ZyxelATP series firmware5.10 through 5.35Not stated
ZyxelUSG FLEX series firmware5.00 through 5.35Not stated
ZyxelUSG FLEX 50(W) firmware5.10 through 5.35Not stated
ZyxelUSG20(W)-VPN firmware5.10 through 5.35Not stated
ZyxelVPN series firmware5.00 through 5.35Not stated
ZyxelUsg Flex 100 Firmware5.00 through 5.35Not stated
ZyxelUsg Flex 100w Firmware5.00 through 5.35Not stated
ZyxelUsg Flex 200 Firmware5.00 through 5.35Not stated
ZyxelUsg Flex 50 Firmware5.00 through 5.35Not stated
ZyxelUsg Flex 50w Firmware5.10 through 5.35Not stated
ZyxelUsg Flex 500 Firmware5.00 through 5.35Not stated
ZyxelUsg Flex 700 Firmware5.00 through 5.35Not stated
ZyxelVpn100 Firmware5.00 through 5.35Not stated
ZyxelVpn1000 Firmware5.00 through 5.35Not stated
ZyxelVpn300 Firmware5.00 through 5.35Not stated
ZyxelVpn50 Firmware5.00 through 5.35Not stated
ZyxelUsg 20w-vpn Firmware5.10 through 5.35Not stated
ZyxelAtp100 Firmware5.10 through 5.35Not stated
ZyxelAtp100w Firmware5.10 through 5.35Not stated
ZyxelAtp200 Firmware5.10 through 5.35Not stated
ZyxelAtp500 Firmware5.10 through 5.35Not stated
ZyxelAtp700 Firmware5.10 through 5.35Not stated
ZyxelAtp800 Firmware5.10 through 5.35Not stated

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
NetworkCan be exploited remotely over a network, including the internet.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
NoneNo account or login is needed.
User interaction
RequiredA user must take an action such as opening a file or link.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
NoneNo data is disclosed.
Integrity
HighData or code can be modified at will.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H. Scored by NVD.

Scoring systemScoreSeverityScored by
CVSS 3.18.1HighCNA (zyxel.com.tw)
CVSS 3.18.1HighNVD

Official description

The 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.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Improper Input Validation

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.

How developers prevent this class of flaw

  • Consider using language-theoretic security (LangSec) techniques that characterize inputs using a formal language and build recognizers for that language. This effectively requires parsing to be a distinct layer that effectively enforces a boundary between raw input and internal data representations, instead of allowing parser code to be scattered throughout the program, where it could be subject to errors or inconsistencies that create weaknesses.
  • Use an input validation framework such as Struts or the OWASP ESAPI Validation API. Note that using a framework does not automatically address all input validation problems; be mindful of weaknesses that could arise from misusing the framework itself (CWE-1173).
  • Understand all the potential areas where untrusted inputs can enter the product, including but not limited to: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide data to the application. Remember that such inputs may be obtained indirectly through API calls.

More Improper Input Validation vulnerabilities (CWE-20)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
  3. Record last changed materially (score, affected products, status or references).

References

Other vulnerabilities in ATP series firmware

All ATP series firmware vulnerabilities

Recent Improper Input Validation vulnerabilities

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