CVE-2023-33009

CRITICALNVD 9.89.8
EchelonGraph scoreHIGH confidence

“—” beside the score: it is equal to NVD's CVSS score.

Score elevated to 9.8 because this CVE is listed on the CISA Known Exploited Vulnerabilities catalog (added 2023-06-05), indicating real-world exploitation has been confirmed by US federal agencies. NVD baseline CVSS 9.8 retained for reference. Confidence: HIGH.

Triggered by: CISA KEV (actively exploited)
Sources: CISA Known Exploited Vulnerabilities catalog, EPSS, GitHub Security Advisory, NVD CVSS v3
Trending — 3 sources updated this weekExploited in the wild
9.8EG
EchelonGraph verdictMitigate nowTreat as an emergency — this is being exploited.
  • Actively exploited in the wild (CISA-KEV) — the reason this is sooner than the SSVC decision on this page at low mission impact
CISA-KEV: ExploitedEPSS PROB: 28%CVSS: 9.8Exploit: No code on recordExposed services: Not assessed

No fix is confirmed yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for the fix.

The CVE record's description, written by its CNA (Zyxel Corporation), states the affected versions: "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…" No release containing a fix is confirmed on record.

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.

CVSS v3
9.8
EG Score
9.8CRITICALhigh confidence
EG Risk
99
EG Risk 99/100

EG Risk is EchelonGraph's 0–100 priority score. It fuses impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.

How it’s computed (value × EchelonGraph’s weight)
Severity98% × 45%
Impact severity (EG Severity): CVSS 9.8 of 10. Never the KEV-floored or EPSS-lifted EG Score.
Exploitation100% × 40%
Fixed at 100% for a CISA KEV listing: EchelonGraph's rule.
Automatability100% × 15%
CISA's SSVC Automatable value: yes (Vulnrichment).
SSVC (CISA's decision table, applied by EchelonGraph): Attend at low mission impact; Act at medium or high.
Exploitation active (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.
Action: No fix is confirmed yet. Restrict network exposure of the affected system or apply the vendor's mitigation sooner than your standard update timelines at low mission impact and as soon as possible at medium or high, and watch the vendor's advisory for the fix.
EPSS PROB
28%
EPSS %ILE
98th
KEV
⚠ Exploited

What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)

The EG score (9.8): severity, escalated by confirmed exploitation. This CVE's 9.8 is its impact severity (EG Severity), not escalated.

EG Severity
9.8 CRITICALCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
EG Likelihood
28% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-22). FIRST's exploitation probability, not an EchelonGraph model.
Confirmed exploitation
CISA KEV and EG-KEV Tier 1 (exploited in the wild)Reported apart from the likelihood: an observed fact, not a probability.
EG Priority
SSVC Act at medium mission impactAttend at low mission impact; Act at medium or high.CISA BOD 26-04: 3 days & forensic triage if the affected system is publicly exposed; 3 days & forensic triage if it is not.Each input and its source: the SSVC and BOD 26-04 blocks below.

SSVC (CISA's decision table, applied by EchelonGraph)Attend at low mission impact; Act at medium or high.

No fix is confirmed yet. Restrict network exposure of the affected system or apply the vendor's mitigation sooner than your standard update timelines at low mission impact and as soon as possible at medium or high, and watch the vendor's advisory for the fix.

Exploitation active (CISA Vulnrichment) · Automatable yes (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table

BOD 26-04 (CISA's remediation timeline, Table 1)3 days & forensic triage if the affected system is publicly exposed; 3 days & forensic triage if it is not.

In CISA KEV yes (CISA's KEV catalog) · Automatable yes (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it

CISA required action“Apply updates per vendor instructions.”

Quoted verbatim from CISA's Known Exploited Vulnerabilities catalog. CISA directs it at US federal civilian executive branch agencies under Binding Operational Directive (BOD) 26-04, which replaced BOD 22-01 on 10 June 2026; it is not EchelonGraph's advice. CISA's notes: https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-multiple-buffer-overflow-vulnerabilities-of-firewalls · https://nvd.nist.gov/vuln/detail/CVE-2023-33009

Published

May 24, 2023

Last Modified

February 26, 2026

Advisory Details (2)

Auto-updated Oct 23, 2026
⚠️ Actively exploited (CISA KEV, CISA Vulnrichment). No fix on record yet. Sources: cisa.
CISA🔴 Active Exploitation

Known Exploited Vulnerabilities Catalog | CISA

Known Exploited Vulnerabilities Catalog | CISA. Listed in CISA Known Exploited Vulnerabilities catalog.

https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2023-33009
Web page

Zyxel security advisory for multiple buffer overflow vulnerabilities of firewalls | Zyxel Networks

https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-multiple-buffer-overflow-vulnerabilities-of-firewalls

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 19× in last 7d / 183× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.

Showing the most recent 100 of 1,117 refreshes on record for this CVE.

A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. None are among the latest 100 rows. The 1,017 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-10-23 16:29 UTCEPSS rescoreEPSS 28% · 98th percentile
  2. 2026-10-23 06:16 UTCEG score recompute
  3. 2026-10-23 06:16 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  4. 2026-10-22 16:31 UTCEPSS rescoreEPSS 28% · 98th percentile
  5. 2026-10-22 04:02 UTCEG score recompute
  6. 2026-10-22 04:02 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  7. 2026-10-21 16:29 UTCEPSS rescoreEPSS 28% · 98th percentile
  8. 2026-10-21 01:48 UTCEG score recompute
  9. 2026-10-21 01:48 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  10. 2026-10-20 16:29 UTCEPSS rescoreEPSS 28% · 98th percentile
  11. 2026-10-19 23:34 UTCEG score recompute
  12. 2026-10-19 23:34 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  13. 2026-10-19 16:29 UTCEPSS rescoreEPSS 28% · 98th percentile
  14. 2026-10-18 21:19 UTCEG score recompute
  15. 2026-10-18 21:19 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  16. 2026-10-18 08:00 UTCEG score recompute
  17. 2026-10-17 19:04 UTCEG score recompute
  18. 2026-10-17 19:04 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  19. 2026-10-17 16:29 UTCEPSS rescoreEPSS 28% · 98th percentile
  20. 2026-10-16 16:50 UTCEG score recompute
  21. 2026-10-16 16:50 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  22. 2026-10-16 16:35 UTCEPSS rescoreEPSS 28% · 98th percentile
  23. 2026-10-15 16:29 UTCEPSS rescoreEPSS 28% · 98th percentile
  24. 2026-10-15 14:34 UTCEG score recompute
  25. 2026-10-15 14:34 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
Show 75 more
  1. 2026-10-14 16:29 UTCEPSS rescoreEPSS 28% · 98th percentile
  2. 2026-10-14 12:19 UTCEG score recompute
  3. 2026-10-14 12:19 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  4. 2026-10-13 16:30 UTCEPSS rescoreEPSS 28% · 98th percentile
  5. 2026-10-13 10:04 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  6. 2026-10-12 18:26 UTCEG score recompute
  7. 2026-10-12 16:30 UTCEPSS rescoreEPSS 28% · 98th percentile
  8. 2026-10-12 07:49 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  9. 2026-10-12 03:49 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  10. 2026-10-11 23:48 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  11. 2026-10-11 19:46 UTCEG score recompute
  12. 2026-10-11 19:46 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  13. 2026-10-11 15:46 UTCEG score recompute
  14. 2026-10-11 15:46 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  15. 2026-10-11 13:45 UTCEPSS rescoreEPSS 28% · 98th percentile
  16. 2026-10-11 11:46 UTCEG score recompute
  17. 2026-10-11 11:46 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  18. 2026-10-11 07:46 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  19. 2026-10-11 03:44 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  20. 2026-10-10 23:44 UTCEG score recompute
  21. 2026-10-10 23:43 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  22. 2026-10-10 19:57 UTCEPSS rescoreEPSS 28% · 98th percentile
  23. 2026-10-10 19:43 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  24. 2026-10-10 15:43 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  25. 2026-10-10 11:42 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  26. 2026-10-10 07:42 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  27. 2026-10-10 03:42 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  28. 2026-10-09 23:42 UTCEG score recompute
  29. 2026-10-09 23:42 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  30. 2026-10-09 20:05 UTCEPSS rescoreEPSS 28% · 98th percentile
  31. 2026-10-09 19:41 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  32. 2026-10-09 15:42 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  33. 2026-10-09 11:41 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  34. 2026-10-09 07:40 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  35. 2026-10-09 03:40 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  36. 2026-10-08 23:40 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  37. 2026-10-08 19:40 UTCEG score recompute
  38. 2026-10-08 19:39 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  39. 2026-10-08 17:06 UTCEPSS rescoreEPSS 28% · 98th percentile
  40. 2026-10-08 15:39 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  41. 2026-10-08 11:38 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  42. 2026-10-08 07:37 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  43. 2026-10-08 03:38 UTCEG score recompute
  44. 2026-10-08 03:38 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  45. 2026-10-07 23:46 UTCEPSS rescoreEPSS 28% · 98th percentile
  46. 2026-10-07 23:37 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  47. 2026-10-07 19:37 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  48. 2026-10-07 15:37 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  49. 2026-10-07 11:37 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  50. 2026-10-07 07:36 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  51. 2026-10-07 03:35 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  52. 2026-10-06 23:33 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  53. 2026-10-06 19:33 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  54. 2026-10-06 15:32 UTCEG score recompute
  55. 2026-10-06 15:31 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  56. 2026-10-06 15:15 UTCEPSS rescoreEPSS 28% · 98th percentile
  57. 2026-10-06 11:31 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  58. 2026-10-06 07:31 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  59. 2026-10-06 03:31 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  60. 2026-10-06 03:30 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  61. 2026-10-05 23:29 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  62. 2026-10-05 19:29 UTCEG score recompute
  63. 2026-10-05 19:29 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  64. 2026-10-05 17:41 UTCEPSS rescoreEPSS 28% · 98th percentile
  65. 2026-10-05 15:29 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  66. 2026-10-05 11:28 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  67. 2026-10-05 07:29 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  68. 2026-10-05 03:29 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  69. 2026-10-04 23:28 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  70. 2026-10-04 19:29 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  71. 2026-10-04 15:29 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  72. 2026-10-04 11:28 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  73. 2026-10-04 07:28 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  74. 2026-10-04 03:28 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8
  75. 2026-10-03 23:28 UTCGHSA enrichmentGHSA-g3f9-6h7x-x69v · GitHub severity CRITICAL · GitHub CVSS 9.8

Frequently asked(6)

What is CVE-2023-33009?
CVE-2023-33009 is a critical-severity vulnerability; its CVE record was published on May 24, 2023. 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…
When was the CVE record for CVE-2023-33009 published?
The CVE record for CVE-2023-33009 was published on May 24, 2023. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of February 26, 2026; the record at its source may have been updated since.
Is CVE-2023-33009 actively exploited?
Yes. CISA added CVE-2023-33009 to the Known Exploited Vulnerabilities catalog on June 5, 2023, affecting Zyxel Multiple Firewalls. KEV listing indicates confirmed exploitation in the wild; this CVE warrants immediate attention. No fix is confirmed yet. Restrict network exposure of the affected system or apply the vendor's mitigation, and watch the vendor's advisory for the fix.
What is the CVSS score of CVE-2023-33009?
CVE-2023-33009 has a CVSS v3 base score of 9.8 (NVD).
Which products are affected by CVE-2023-33009?
CVE-2023-33009 affects Zyxel Multiple Firewalls.
How do I remediate CVE-2023-33009?
No fix for CVE-2023-33009 is confirmed yet. Until one is published, restrict network exposure of the affected system or apply the vendor's mitigation — for example, keep it off the internet or limit it to trusted networks — and watch the vendor's advisory for the fix. The CVE record's description, written by its CNA (Zyxel Corporation), states the affected versions: "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…" No release containing a fix is confirmed on record.

Dependency Blast Radius

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