Zyxel USG FLEX/VPN up to 5.35 HTTP Request fbwifi_forward.cgi buffer overflow

Summaryinfo

A vulnerability categorized as critical has been discovered in Zyxel USG FLEX and VPN up to 5.35. This affects an unknown function of the file fbwifi_forward.cgi of the component HTTP Request Handler. Such manipulation leads to buffer overflow. This vulnerability is uniquely identified as CVE-2023-22915. The attack can be launched remotely. No exploit exists.

Detailsinfo

A vulnerability was found in Zyxel USG FLEX and VPN up to 5.35 (Network Encryption Software). It has been rated as critical. Affected by this issue is an unknown functionality of the file fbwifi_forward.cgi of the component HTTP Request Handler. The manipulation with an unknown input leads to a buffer overflow vulnerability. Using CWE to declare the problem leads to CWE-120. The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer, leading to a buffer overflow. Impacted is availability. CVE summarizes:

A buffer overflow vulnerability in the “fbwifi_forward.cgi” CGI program of Zyxel USG FLEX series firmware versions 4.50 through 5.35, USG FLEX 50(W) firmware versions 4.30 through 5.35, USG20(W)-VPN firmware versions 4.30 through 5.35, and VPN series firmware versions 4.30 through 5.35, which could allow a remote unauthenticated attacker to cause DoS conditions by sending a crafted HTTP request if the Facebook WiFi function were enabled on an affected device.

The weakness was disclosed 04/24/2023. The advisory is shared for download at zyxel.com. This vulnerability is handled as CVE-2023-22915 since 01/10/2023. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $5k-$25k (estimation calculated on 10/05/2025).

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-2023-27017). VulDB is the best source for vulnerability data and more expert information about this specific topic.

Productinfo

Type

• Network Encryption Software

Vendor

• Zyxel

Name

• 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

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VulDB is the best source for vulnerability data and more expert information about this specific topic.

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