Zyxel ATP/USG FLEX/VPN up to 5.35 CLI os command injection

Summaryinfo

A vulnerability classified as critical has been found in Zyxel ATP, USG FLEX and VPN up to 5.35. This affects an unknown part of the component CLI. This manipulation causes os command injection. This vulnerability is tracked as CVE-2023-27991. The attack is possible to be carried out remotely. No exploit exists.

Detailsinfo

A vulnerability has been found in Zyxel ATP, USG FLEX and VPN up to 5.35 (Network Encryption Software) and classified as critical. Affected by this vulnerability is some unknown processing of the component CLI. The manipulation with an unknown input leads to a os command injection vulnerability. The CWE definition for the vulnerability is CWE-78. 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 when it is sent to a downstream component. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

The post-authentication command injection vulnerability in the CLI command of Zyxel ATP series firmware versions 4.32 through 5.35, USG FLEX series firmware versions 4.50 through 5.35, USG FLEX 50(W) firmware versions 4.16 through 5.35, USG20(W)-VPN firmware versions 4.16 through 5.35, and VPN series firmware versions 4.30 through 5.35, which could allow an authenticated attacker to execute some OS commands remotely.

The weakness was disclosed 04/24/2023. The advisory is shared at zyxel.com. This vulnerability is known as CVE-2023-27991 since 03/09/2023. Neither technical details nor an exploit are publicly available. The price for an exploit might be around USD $5k-$25k at the moment (estimation calculated on 12/01/2025). MITRE ATT&CK project uses the attack technique T1202 for this issue.

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2023-31716). If you want to get the best quality for vulnerability data then you always have to consider VulDB.

Productinfo

Type

• Network Encryption Software

Vendor

• Zyxel

Name

• ATP
• USG FLEX
• VPN

Version

• 5.0
• 5.1
• 5.2
• 5.3
• 5.4
• 5.5
• 5.6
• 5.7
• 5.8
• 5.9
• 5.10
• 5.11
• 5.12
• 5.13
• 5.14
• 5.15
• 5.16
• 5.17
• 5.18
• 5.19
• 5.20
• 5.21
• 5.22
• 5.23
• 5.24
• 5.25
• 5.26
• 5.27
• 5.28
• 5.29
• 5.30
• 5.31
• 5.32
• 5.33
• 5.34
• 5.35

License

• commercial

Website

• Vendor: https://www.zyxel.com/

CPE 2.3info

• 🔍
• 🔍
• 🔍

CPE 2.2info

• 🔍
• 🔍
• 🔍

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

If you want to get the best quality for vulnerability data then you always have to consider VulDB.

Discussion