CyberSecBulletin
CVE-2023-22913NVD status: Modified

USG FLEX series firmware: Improper Neutralization of Special Elements used in a Command

Published Updated By the CyberSecBulletin desk

CVE-2023-22913 is a high-severity improper neutralization of special elements used in a command vulnerability in USG FLEX 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 attacker with a low-privileged account, without any action from a user. Affected USG FLEX series firmware versions: 4.50 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 1.29% chance of exploitation within 30 days, higher than 71% of scored CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Check which version of USG FLEX 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.

Affected products and versions

VendorProductAffected versionsFixed in
ZyxelUSG FLEX series firmware4.50 through 5.35Not stated
ZyxelVPN series firmware4.30 through 5.35Not stated
ZyxelUsg Flex 100 Firmware4.50 through 5.35Not stated
ZyxelUsg Flex 100w Firmware4.50 through 5.35Not stated
ZyxelUsg Flex 200 Firmware4.50 through 5.35Not stated
ZyxelUsg Flex 50 Firmware4.50 through 5.35Not stated
ZyxelUsg Flex 50w Firmware4.50 through 5.35Not stated
ZyxelUsg Flex 500 Firmware4.50 through 5.35Not stated
ZyxelUsg Flex 700 Firmware4.50 through 5.35Not stated
ZyxelVpn100 Firmware4.50 through 5.35Not stated
ZyxelVpn1000 Firmware4.50 through 5.35Not stated
ZyxelVpn300 Firmware4.50 through 5.35Not stated
ZyxelVpn50 Firmware4.50 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
LowA basic user account is enough.
User interaction
NoneNo action by a victim is required.
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:L/UI:N/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

A post-authentication command injection vulnerability in the “account_operator.cgi” CGI program of Zyxel USG FLEX series firmware versions 4.50 through 5.35, and VPN series firmware versions 4.30 through 5.35, which could allow a remote authenticated attacker to modify device configuration data, resulting in denial-of-service (DoS) conditions on an affected device.

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

The underlying weakness: Improper Neutralization of Special Elements used in a Command

The product constructs all or part of a command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended command when it is sent to a downstream component.

How developers prevent this class of flaw

  • If at all possible, use library calls rather than external processes to recreate the desired functionality.
  • If possible, ensure that all external commands called from the program are statically created.
  • Run time: Run time policy enforcement may be used in an allowlist fashion to prevent use of any non-sanctioned commands.

More Improper Neutralization of Special Elements used in a Command vulnerabilities (CWE-77)

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 USG FLEX series firmware

All USG FLEX series firmware vulnerabilities

Recent Improper Neutralization of Special Elements used in a Command vulnerabilities

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