CVE-2023-6764Network attack vector

Unauthenticated code execution via IPSec format string

Published Feb 20, 2024 · Updated Aug 2, 2024

Format string injection in Zyxel firewall IPSec VPN firmware allows remote attackers to execute arbitrary code via crafted payloads. An undisclosed IPSec VPN function treats attacker-controlled payload data as a format string while processing an invalid pointer. No authentication or user interaction is required, but exploitation depends on detailed knowledge of the device's memory layout and configuration.

CVSS severity8.1
High
EPSS probability0.89%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Format string injection in Zyxel firewall IPSec VPN firmware allows remote attackers to execute arbitrary code via crafted payloads. An undisclosed IPSec VPN function treats attacker-controlled payload data as a format string while processing an invalid pointer. No authentication or user interaction is required, but exploitation depends on detailed knowledge of the device's memory layout and configuration.

The record

CVE
CVE-2023-6764
Published
Feb 20, 2024
Updated
Aug 2, 2024
Vendor
Zyxel Networks
Product
USG20(W)-VPN Series
Classifications
CWE-134, CAPEC-67, CAPEC-135, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 20, 2024CVE publishedPublication date reported by the CVE source.
  2. Aug 2, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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

  1. Affected versionversion=version 4.16 through 5.37 Patch 1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Zyxel Networks · USG20(W)-VPN Seriesversion=version 4.16 through 5.37 Patch 1
Zyxel Networks · USG FLEX 50 Seriesversion=version 4.16 through 5.37 Patch 1
Zyxel Networks · ATP Seriesversion=4.32 <=5.37patch1; version=version 4.32 through 5.37 Patch 1
Zyxel Networks · USG FLEX Seriesversion=4.50 <=5.37patch1; version=version 4.50 through 5.37 Patch 1
Zyxel Networks · USG FLEX 50/50W Seriesversion=4.16 <=5.37patch1

Published CVSS scores

8.1Zyxel CorporationCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-134Use of Externally-Controlled Format String
CAPEC-67String Format Overflow in syslog()
CAPEC-135Format String Injection
T1190Exploit Public-Facing Application

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

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Your stack

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