CyberSecBulletin
CVE-2023-28771Exploited in the wildNVD status: Analyzed

Zyxel Multiple Firewalls OS Command Injection

Published Updated By the CyberSecBulletin desk

CVE-2023-28771 is a critical-severity improper neutralization of special elements used in an OS command vulnerability in ZyWALL/USG series firmware from Zyxel, with a CVSS 3.1 base score of 9.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected ZyWALL/USG series firmware versions: 4.60 through 4.73. The record does not name a fixed version, so check the vendor advisory. CISA added it to the Known Exploited Vulnerabilities catalogue on May 31, 2023, which means attacks have been observed in the wild.

Patch now

Attackers are already exploiting this vulnerability, according to CISA.

What to do

  1. Update Atp100 Firmware to 5.36 or a later version.
  2. Update Atp100w Firmware to 5.35 or a later version.
  3. Update Atp200 Firmware to 5.36 or a later version.
  4. CISA's required action: Apply updates per vendor instructions.
  5. Read the advisory on zyxel.com for workarounds and exact fixed builds.
  6. Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.

Affected products and versions

VendorProductAffected versionsFixed in
ZyxelZyWALL/USG series firmware4.60 through 4.73Not stated
ZyxelVPN series firmware4.60 through 5.35Not stated
ZyxelUSG FLEX series firmware4.60 through 5.35Not stated
ZyxelATP series firmware4.60 through 5.35Not stated
ZyxelAtp100 Firmware4.60 up to, but not including, 5.365.36
ZyxelAtp100w Firmware4.60 up to, but not including, 5.355.35
ZyxelAtp200 Firmware4.60 up to, but not including, 5.365.36
ZyxelAtp500 Firmware4.60 up to, but not including, 5.365.36
ZyxelAtp700 Firmware4.60 up to, but not including, 5.365.36
ZyxelAtp800 Firmware4.60 up to, but not including, 5.365.36
ZyxelUsg Flex 100 Firmware4.60 up to, but not including, 5.365.36
ZyxelUsg Flex 100w Firmware4.60 up to, but not including, 5.365.36
ZyxelUsg Flex 200 Firmware4.60 up to, but not including, 5.365.36
ZyxelUsg Flex 50 Firmware4.60 up to, but not including, 5.365.36
ZyxelUsg Flex 500 Firmware4.60 up to, but not including, 5.365.36
ZyxelUsg Flex 50w Firmware4.60 up to, but not including, 5.365.36
ZyxelUsg Flex 700 Firmware4.60 up to, but not including, 5.365.36
ZyxelVpn100 Firmware4.60 up to, but not including, 5.365.36
ZyxelVpn1000 Firmware4.60 up to, but not including, 5.365.36
ZyxelVpn300 Firmware4.60 up to, but not including, 5.365.36
ZyxelVpn50 Firmware4.60 up to, but not including, 5.365.36
ZyxelZywall Usg 310 Firmware4.60 up to, but not including, 4.73; 4.734.73
ZyxelZywall Usg 100 Firmware4.60 up to, but not including, 4.73; 4.734.73

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
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
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:N/S:U/C:H/I:H/A:H. Scored by NVD.

Scoring systemScoreSeverityScored by
CVSS 3.19.8CriticalCNA (zyxel.com.tw)
CVSS 3.19.8CriticalNVD

Official description

Improper error message handling in Zyxel ZyWALL/USG series firmware versions 4.60 through 4.73, VPN series firmware versions 4.60 through 5.35, USG FLEX series firmware versions 4.60 through 5.35, and ATP series firmware versions 4.60 through 5.35, which could allow an unauthenticated attacker to execute some OS commands remotely by sending crafted packets to 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 an OS Command

The product constructs all or part of an OS command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended OS command before 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.
  • For any data that will be used to generate a command to be executed, keep as much of that data out of external control as possible. For example, in web applications, this may require storing the data locally in the session's state instead of sending it out to the client in a hidden form field.
  • For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.

More Improper Neutralization of Special Elements used in an OS Command vulnerabilities (CWE-78)

Timeline

  1. CVE record published.
  2. Added to CISA's Known Exploited Vulnerabilities catalogue.
  3. Deadline for US federal agencies to remediate, set by CISA.
  4. CISA published its SSVC assessment (exploitation: active, automatable: yes, technical impact: total).
  5. Record last changed materially (score, affected products, status or references).

References

Third-party and government advisories

Technical write-ups (may include proof of concept)

Other vulnerabilities in ZyWALL/USG series firmware

All ZyWALL/USG series firmware vulnerabilities

Recent Improper Neutralization of Special Elements used in an OS Command vulnerabilities

Spotted an error? Tell us.