Threats / Zyxel / CVE-2023-33009
CVE-2023-33009
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-08-04
Zyxel Multiple Firewalls vulnerability
Zyxel firewalls contain a buffer overflow in the notification function allowing unauthenticated remote attackers to cause denial-of-service or execute code.
Verdict
Today item — known-exploited.
An unauthenticated attacker can exploit a buffer overflow vulnerability in multiple Zyxel firewall models to trigger denial-of-service conditions or achieve remote code execution without authentication.
CISA KEV Yes · 2023-06-055EPSS 0.28144 (verify live)6CVSS 9.83CISA SSVC Exploitation: active · Automatable: yes · Impact: total4
01
Is it exploitable?
— the evidence, ranked above the scoreReported exploitation
4 independent public reports of in-the-wild exploitation are cataloged.Distinct reporting sources (vendor, incident response, government); open them for the underlying claims.
Exploited in the wild
Listed in the CISA Known Exploited Vulnerabilities catalog (added 2023-06-05).
Probability (EPSS)
EPSS 0.28144 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
CVSS 9.8 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H) · Affected: Zyxel, Multiple Firewalls. Confirm exact fixed builds in the vendor advisory.CVSS — CNA-assigned (CVE.org), version 3.1, set at disclosure.
Weakness (CWE)
Mapped to CWE-120 Buffer Copy without Size Check — weakness family: Memory safety.CWE — CNA-assigned (CVE.org); the weakness class drives how the flaw is exploited.
CISA SSVC (triage disposition)
Exploitation: active · Automatable: yes · Technical Impact: totalCISA's own stakeholder-specific triage inputs, published in the CVE record (CISA Coordinator role). NOTE: this is CISA's three decision points; the final Act/Attend/Track decision also requires a Mission & Well-being input not published here, so no overall decision is asserted.
Currency of the record
CISA added this to its KEV catalog 12 days after the CVE record was published.KEV lag = CISA-KEV dateAdded − CVE.org datePublished; a floor on how long the known-exploited flaw sat in the public record before the federal catalog listed it. Severity/weakness here is CNA- or CISA-assigned (current at disclosure), independent of NVD's analysis backlog.
02
Who’s exploiting it?
— attribution turns risk into urgencyAttribution not established
No confirmed (advisory-backed) threat-actor attribution is established for this record. Absence of a named actor is not absence of compromise — see Coverage & confidence.
03
Why it matters
— the attack path, told twice: adversary, then board1
Front door — unauthenticated access narrative 1
Attacker
I craft a malicious input to the notification function that exceeds buffer boundaries.
Business
The firewall becomes unstable or unresponsive, disrupting network traffic and security operations.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I leverage the overflow to inject and execute arbitrary code on the compromised firewall.
Business
The attacker gains control of a critical security perimeter device, enabling lateral movement and data exfiltration.
04
What to do
— defensible action- Remediate per the vendor advisory — confirm the fixed build for your version and verify exposure.1
Say it to the boardA vulnerability with this evidence profile is a defensible budget line, not a backlog ticket — fund the change against the proof above.
05