Home/CVE/A format string vulnerability in the Zyxel ATP series firmware versions 5.10 through 5.36 Patch 2, USG FLEX series firmw
CVE
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CVE-2023-33011

A format string vulnerability in the Zyxel ATP series firmware versions 5.10 through 5.36 Patch 2, USG FLEX series firmw

A format string vulnerability in the Zyxel ATP series firmware versions 5.10 through 5.36 Patch 2, USG FLEX series firmware versions 5.00 through 5.36 Patch 2, USG FLEX 50(W) series firmware versions 5.10 through 5.36 Patch 2, USG20(W)-VPN series firmware versions 5.10 through 5.36 Patch 2, and VPN series firmware versions 5.00 through 5.36 Patch 2, could allow an unauthenticated, LAN-based attacker to execute some OS commands by using a crafted PPPoE configuration on an affected device when the cloud management mode is enabled.

HIGH · CVSS 8.8 EPSS 0.0034
EPSS exploitation odds0.34% · top 73%
Schedule remediation
  • CVSS base score ≥ 7.0
No Sigma yet — build one → YARA rules0
Look this up elsewhere - one-click external pivots
NVDCVE.orgCISAExploit-DBGitHub PoCVulnCheck KEVGreyNoise
▸ How to read a CVE - triage first, then detect and patch
This page is every public fact about CVE-2023-33011, cross-linked. Its job is to answer one question fast - does this need my attention now? - and then hand you the two things you do about it. Here is how an analyst reads it.
Triage: should I act now? Four signals, and they are not interchangeable:
CVSSseverity - how bad it is IF exploited, 0-10. A high CVSS alone is not urgency; a flaw can be a perfect 10 and never actually be attacked. EPSSprobability - a model’s estimate of the chance it is exploited in the next 30 days, 0-1. This is the “will it actually happen” signal. CISA KEVconfirmed - it is being exploited in the wild right now. The strongest signal on the page; KEV beats any score. Weaponisedavailability - public exploits / PoCs, and especially Metasploit modules rated Excellent / Great. Reliable, packaged exploit code means low-skill attackers can use it today.
How they combine: KEV, or a dependable Metasploit module, means patch now regardless of CVSS. High CVSS + low EPSS + no exploit is real but not an emergency - schedule it. Low CVSS but KEV-listed still gets patched now. The verdict above already weighed these for you; this is how it got there.
Then what - two workflows:
Detectwhen you cannot patch today, follow this CVE to the ATT&CK techniques it enables, then Build a SIEM detection (the green button) - author a rule, test it in Atomic, deploy it. That buys visibility while the patch waits. PatchAffected products / packages tell you if you are exposed; Fixed versions by distribution and Vendor advisories give the exact version that closes it.
Reading order for the panels below: verdict + badges, then Public exploits / Metasploit (is it weaponised), then ATT&CK techniques + Sigma / IDS rules (can I detect it), then Affected products / packages + Fixed versions (am I exposed, what patches it), then Threat actors / IOCs (who uses it), then Scoring & timeline / references (the evidence).
▣

Severity & exploitation scoring

View on NVD →
CVSS base score
8.8
HIGHCVSS v3.1 · [email protected]
EPSS exploitation probability
0.34%
Top 73%odds of exploitation in the next 30 days
CVSS metric silhouette
VectorComplexityPrivilegesInteractionScopeConfidentialityIntegrityAvailability
shape grows toward worst-case
SSVC triage · cisa-vulnrichment
Exploitation
none
Automatable
no
Tech impact
total
CVSS vector breakdown
Exploitability - how they get in
Attack Vector
Network Adjacent Local Physical
Attack Complexity
Low High
Privileges Required
None Low High
User Interaction
None Required
Scope
Unchanged Changed
Impact - what breaks
Confidentiality
None Low High
Integrity
None Low High
Availability
None Low High
VECTORCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Lifecycle
  1. 17 Jul 2023Published to NVD
  2. 17 Jun 2026Last modified
Every entry is a recorded date - NVD publish/modify, CISA KEV add, public exploit disclosure. No inferred events.
Attack path
Full kill chain
→
◆

ATT&CK techniques

1

Techniques this CVE enables. Pills with a solid outline are high confidence - named directly in ATT&CK or Nuclei, or human-curated by CTID; the rest are inferred from the weakness type using MITRE's CVE Mapping Methodology and the CWE → CAPEC chain. Broad, generic-weakness guesses are filtered out. A small N× marks a technique that N independent sources agree on.

T1210 · Exploitation of Remote Services
▤ Build a SIEM detection for these techniques
▤

CAPEC attack patterns

2

Attack patterns this CVE enables - the bridge from weakness to ATT&CK technique.

CAPEC-CAPEC-135 · Format String Injection CAPEC-CAPEC-67 · String Format Overflow in syslog()
⬡

Weakness Classification

CWE-134Use of Externally-Controlled Format String
CWE-134Use of Externally-Controlled Format String
▤

Affected Products & Versions

22
zyxel usg 2200-vpn firmware>= 5.00 and < 5.37
zyxel usg flex 100 firmware>= 5.00 and < 5.37
zyxel usg flex 100w firmware>= 5.00 and < 5.37
zyxel usg flex 200 firmware>= 5.00 and < 5.37
zyxel usg flex 50 firmware>= 5.00 and < 5.37
zyxel usg flex 500 firmware>= 5.00 and < 5.37
zyxel usg flex 50w firmware>= 5.00 and < 5.37
zyxel usg flex 700 firmware>= 5.00 and < 5.37
zyxel zywall vpn100 firmware>= 5.00 and < 5.37
zyxel zywall vpn2s firmware>= 5.00 and < 5.37
zyxel zywall vpn300 firmware>= 5.00 and < 5.37
zyxel zywall vpn50 firmware>= 5.00 and < 5.37
zyxel zywall vpn 100 firmware>= 5.00 and < 5.37
zyxel zywall vpn 300 firmware>= 5.00 and < 5.37
zyxel zywall vpn 50 firmware>= 5.00 and < 5.37
zyxel usg 20w-vpn firmware>= 5.10 and < 5.37
zyxel zywall atp100 firmware>= 5.10 and < 5.37
zyxel zywall atp100w firmware>= 5.10 and < 5.37
zyxel zywall atp200 firmware>= 5.10 and < 5.37
zyxel zywall atp500 firmware>= 5.10 and < 5.37
zyxel zywall atp700 firmware>= 5.10 and < 5.37
zyxel zywall atp800 firmware>= 5.10 and < 5.37
▤

Related CVEs

8
CVEs linked to this one by a shared weakness (CWE) or affected product - joins on data already in the engine, with the reason shown per row.
CVE-2002-0159 Format string vulnerability in the administration function in Cisco Secure Acces... same CWE-134 CVE-2003-0738 The calendar module in phpWebSite 0.9.x and earlier allows remote attackers to c... same CWE-134 CVE-2003-1381 Format string vulnerability in AMX 0.9.2 and earlier, a plugin for Valve Softwar... 1 same CWE-134 CVE-2004-0179 Multiple format string vulnerabilities in (1) neon 0.24.4 and earlier, and other... 1 same CWE-134 CVE-2018-9129 ZyXEL ZyWALL/USG series devices have a Bleichenbacher vulnerability in their Int... same product MEDIUM CVE-2020-25014 A stack-based buffer overflow in fbwifi_continue.cgi on Zyxel UTM and VPN series... same product CRITICAL CVE-2022-0734 A cross-site scripting vulnerability was identified in the CGI program of Zyxel ... same product MEDIUM CVE-2022-0910 A downgrade from two-factor authentication to one-factor authentication vulnerab... same product MEDIUM
🔗

References & Sources

1
Source URLs (vendor pages, mailing lists, write-ups). Exploit/PoC links are in their own section above to avoid duplication.
https://www.zyxel.com/global/en/support/security-advisories/zyxel-security-advisory-for-multiple-vulnerabilities-in-firewalls-and-wlan-controllers
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