CVE-2023-22915Network attack vector

Service interruption via fbwifi_forward.cgi buffer overflow

Published Apr 24, 2023 · Updated Feb 12, 2025

Buffer overflow in fbwifi_forward.cgi in Zyxel firewall firmware allows remote attackers to interrupt service via a crafted HTTP request. The CGI program copies request-controlled input into a destination buffer without checking its length, overflowing that buffer. The request is reachable only when Facebook WiFi is enabled, and WAN access to the firewall is disabled by default.

CVSS severity7.5
High
EPSS probability1.05%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Buffer overflow in fbwifi_forward.cgi in Zyxel firewall firmware allows remote attackers to interrupt service via a crafted HTTP request. The CGI program copies request-controlled input into a destination buffer without checking its length, overflowing that buffer. The request is reachable only when Facebook WiFi is enabled, and WAN access to the firewall is disabled by default.

The record

CVE
CVE-2023-22915
Published
Apr 24, 2023
Updated
Feb 12, 2025
Vendor
Zyxel Networks
Product
Zyxel USG FLEX 50(W) Firmware
Classifications
CWE-120, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 24, 2023CVE publishedPublication date reported by the CVE source.
  2. Feb 12, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=4.30 through 5.35

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Zyxel Networks · Zyxel USG FLEX 50(W) Firmwareversion=4.30 through 5.35
Zyxel Networks · Zyxel VPN Series Firmwareversion=4.30 through 5.35
Zyxel Networks · Zyxel USG FLEX Series Firmwareversion=4.50 through 5.35

Published CVSS scores

7.5NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo