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CVE-2023-33009· NVD / CVE Program· CNA Zyxel

A buffer overflow vulnerability in the notification function in Zyxel ATP series firmware versions 4.60 through 5.36 Patch 1, USG FLEX serie

A buffer overflow vulnerability in the notification function in Zyxel ATP series firmware versions 4.60 through 5.36 Patch 1, USG FLEX series firmware versions 4.60 through 5.36 Patch 1, USG FLEX 50(W) firmware versions 4.60 through 5.36 Patch 1, USG20(W)-VPN firmware versions 4.60 through 5.36 Patch 1, VPN series firmware versions 4.60 through 5.36 Patch 1, ZyWALL/USG series firmware versions 4.60 through 4.73 Patch 1, could allow an unauthenticated attacker to cause denial-of-service (DoS) conditions and even a remote code execution on an affected device.

CriticalCVSS 9.8 · v3.1KEVWeaponized No fix recorded
Published
May 24, 2023
Updated
Jun 17, 2026
EPSS
28.1% · 98th percentile
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Action score

77

This week

Don’t wait for the next maintenance window.

CVSS
39 / 40 · 9.8 / 10
CISA KEV
30 / 30 · Listed
EPSS
8 / 30 · 28.1%

CISA SSVC decision

Exploitation
active
Automatable
yes
Technical impact
total

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · Zyxel
9.8
NVD has not scored this yet; the score shown is the CNA’s.

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

Actively exploited in the wild

CISA added this to its Known Exploited Vulnerabilities catalog on Jun 5, 2023. That signals real attacks, not theory.

Remediation deadline for government agencies: Jun 26, 2023.

Affected systems

VendorProduct
zyxelatp100 firmware
zyxelatp100
zyxelatp200 firmware
zyxelatp200
zyxelatp500 firmware
zyxelatp500
zyxelatp100w firmware
zyxelatp100w
zyxelatp700 firmware
zyxelatp700
zyxelatp800 firmware
zyxelatp800

and 34 more

Affected versions

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

  • zyxel atp100 firmware4.60 and later · before 5.36
  • zyxel atp100 firmware5.36
  • zyxel atp100w firmware4.60 and later · before 5.36
  • zyxel atp100w firmware5.36
  • zyxel atp200 firmware4.60 and later · before 5.36
  • zyxel atp200 firmware5.36
  • zyxel atp500 firmware4.60 and later · before 5.36
  • zyxel atp500 firmware5.36
  • zyxel atp700 firmware4.60 and later · before 5.36
  • zyxel atp700 firmware5.36
  • zyxel atp800 firmware4.60 and later · before 5.36
  • zyxel atp800 firmware5.36
  • zyxel usg 20w-vpn firmware4.60 and later · before 5.36
  • zyxel usg 20w-vpn firmware5.36
  • zyxel usg 40 firmware4.60 and later · before 4.73
  • zyxel usg 40 firmware4.73
  • zyxel usg 40w firmware4.60 and later · before 4.73
  • zyxel usg 40w firmware4.73
  • zyxel usg 60 firmware4.60 and later · before 4.73
  • zyxel usg 60 firmware4.73

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

    • 4.60 through 5.36 Patch 1affected

  • Zyxel USG FLEX 50(W) firmware

    • 4.60 through 5.36 Patch 1affected

  • Zyxel USG FLEX series firmware

    • 4.60 through 5.36 Patch 1affected

  • Zyxel USG20(W)-VPN firmware

    • 4.60 through 5.36 Patch 1affected

  • Zyxel VPN series firmware

    • 4.60 through 5.36 Patch 1affected

  • Zyxel ZyWALL/USG series firmware

    • 4.60 through 4.73 Patch 1affected

Same product

zyxel: all records

Other highest-scoring records for the same primary product.

  • CVE-2023-28771Improper error message handling in Zyxel ZyWALL/USG series firmware versions 4.60 through 4.73, VPN series firmware versions 4.60 through 5.KEV
    99Now
  • CVE-2023-33010A buffer overflow vulnerability in the ID processing function in Zyxel ATP series firmware versions 4.32 through 5.36 Patch 1, USG FLEX seriKEV
    78This week
  • CVE-2023-6764 A format string vulnerability in a function of the IPSec VPN feature in Zyxel ATP series firmware versions from 4.32 through 5.3
    32Monitor
  • CVE-2022-38547A post-authentication command injection vulnerability in the CLI command of Zyxel ZyWALL/USG series firmware versions 4.20 through 4.72, VPN
    29Monitor
  • CVE-2023-6398A post-authentication command injection vulnerability in the file upload binary in Zyxel ATP series firmware versions from 4.32 through 5.37
    28Monitor
  • CVE-2023-6399A format string vulnerability in Zyxel ATP series firmware versions from 4.32 through 5.37 Patch 1, USG FLEX series firmware versions from 4
    26Monitor

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

Weaponized

A ready exploit tool or active in-the-wild use is known for this vulnerability. This should be your top priority.

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.

  1. Published
  2. CISA KEV+12 d
  3. TodaySep 29, 2026+1225 d
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).

Technical details

Attack conditions

  • 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.

If successful

Confidentiality
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

CWE-120 · Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')

CVSS vector

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

nvd-secondary

Root cause

When data is copied, the source length is not compared with the size of the destination buffer. Excess data overwrites adjacent memory.

The bug in code

The whole CWE-120 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

c
char buf[256];memcpy(buf, pkt->data, pkt->len);

Fixed

c
char buf[256];if (pkt->len > sizeof(buf)) {  return -EINVAL;}memcpy(buf, pkt->data, pkt->len);

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

Noroxi analysis

No Noroxi analysis for this record yet

We don't hand-write analysis for all 385,000+ vulnerabilities; that wouldn't be honest. For notable, high-impact vulnerabilities our team writes the mechanism, detection and remediation steps.

We use this product, ask for help

Change log

No changes recorded on tracked fields yet. Score, KEV, exploit maturity and fix status changes appear here.

References

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records