NVD / CVE Program· CNA Zyxel

CVE-2023-4398: An integer overflow vulnerability in the source code of the QuickSec IPSec toolkit used in the VPN feature of the Zyxel ATP series firmware

Noroxi assessment

Priority: Monitor (action score 30/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.88% (FIRST EPSS); higher than 58.8% of all records.
Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
According to CISA the attack is automatable: targets can be found by mass scanning.
According to the record, no fixed version is available yet.
Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Update when a fix is released; follow the vendor's advisory.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

An integer overflow vulnerability in the source code of the QuickSec IPSec toolkit used in the VPN feature of the Zyxel ATP series firmware versions 4.32 through 5.37, USG FLEX series firmware versions 4.50 through 5.37, USG FLEX 50(W) series firmware versions 4.16 through 5.37, USG20(W)-VPN series firmware versions 4.16 through 5.37, and VPN series firmware versions 4.30 through 5.37, could allow an unauthenticated attacker to cause denial-of-service (DoS) conditions on an affected device by sending a crafted IKE packet.

HighCVSS 7.5 · v3.1—No exploit No fix recorded

BDU:2023-08213

Published: Nov 27, 2023
Updated: Jun 17, 2026
EPSS: 0.8% · 58th percentile
CWE: CWE-190

Report tools

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Action score

Monitor

Low priority for now.

CVSS: 30 / 40 · 7.5 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.8%

CISA SSVC decision

Exploitation: none
Automatable: yes
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: 7.5
CNA · Zyxel: 7.5; agree

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
No fixed version yet

If any of these changes, we'll tell you in the daily email digest.

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
zyxel	zld	cpe:2.3:o:zyxel:zld
zyxel	atp100	cpe:2.3:h:zyxel:atp100
zyxel	atp100w	cpe:2.3:h:zyxel:atp100w
zyxel	atp200	cpe:2.3:h:zyxel:atp200
zyxel	atp500	cpe:2.3:h:zyxel:atp500
zyxel	atp700	cpe:2.3:h:zyxel:atp700
zyxel	atp800	cpe:2.3:h:zyxel:atp800
zyxel	usg flex 100	cpe:2.3:h:zyxel:usg_flex_100
zyxel	usg flex 100w	cpe:2.3:h:zyxel:usg_flex_100w
zyxel	usg flex 200	cpe:2.3:h:zyxel:usg_flex_200
zyxel	usg flex 50	cpe:2.3:h:zyxel:usg_flex_50
zyxel	usg flex 500	cpe:2.3:h:zyxel:usg_flex_500

and 8 more

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

zyxel zld4.32 and later · up to 5.37 inclusive
zyxel zld4.50 and later · up to 5.37 inclusive
zyxel zld4.16 and later · up to 5.37 inclusive
zyxel zld4.30 and later · up to 5.37 inclusive

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Zyxel). Independent of NVD's CPE analysis and usually ahead of it.

Zyxel ATP series firmware
- versions 4.32 through 5.37affected
Zyxel USG FLEX 50(W) series firmware
- versions 4.16 through 5.37affected
Zyxel USG FLEX series firmware
- versions 4.50 through 5.37affected
Zyxel USG20(W)-VPN series firmware
- versions 4.16 through 5.37affected
Zyxel VPN series firmware
- versions 4.30 through 5.37affected

Same product

zyxel: all records

Other highest-scoring records for the same primary product.

CVE-2024-11667A directory traversal vulnerability in the web management interface of Zyxel ATP series firmware versions V5.00 through V5.38, USG FLEX seriKEV
70This week
CVE-2020-25014A stack-based buffer overflow in fbwifi_continue.cgi on Zyxel UTM and VPN series of gateways running firmware version V4.30 through to V4.55
40Plan
CVE-2025-9133A missing authorization vulnerability in Zyxel ATP series firmware versions from V4.32 through V5.40, USG FLEX series firmware versions from
34Monitor

Published before and after this one in the same product

← EarlierCVE-2023-37926Nov 27, 2023 · A buffer overflow vulnerability in the Zyxel ATP series firmware versions 4.32 through 5.37, USG FLEX series firmware versions 4.50 through
22Monitor
← EarlierCVE-2023-4397Nov 27, 2023 · A buffer overflow vulnerability in the Zyxel ATP series firmware version 5.37, USG FLEX series firmware version 5.37, USG FLEX 50(W) series
17Monitor
Later →CVE-2023-5650Nov 27, 2023 · An improper privilege management vulnerability in the ZySH of the Zyxel ATP series firmware versions 4.32 through 5.37, USG FLEX series firm
22Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

No fix version is recorded for this entry. Check the references for vendor advisories.

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).