Threats / Zyxel / CVE-2023-33009
CVE-2023-33009
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-06-22
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.
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
Affected: Zyxel, Multiple Firewalls. Confirm exact fixed builds in the vendor advisory.
Weakness (CWE)
Mapped to CWE-120 Buffer Copy without Size Check — weakness family: Memory safety.CWE assignment from the public NVD record; the weakness class drives how the flaw is exploited.
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