CriticalCVE-2024-11667

    Zyxel Multiple Firewalls Path Traversal Vulnerability (CVE-2024-11667)

    Published In CISA KEV since Sources: pwn.watch, CVE.org

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    What is affected, what to do

    A directory traversal vulnerability in the web management interface of Zyxel ATP series firmware versions V5.00 through V5.38, USG FLEX series firmware versions V5.00 through V5.38, USG FLEX 50(W) series firmware versions V5.10 through V5.38, and USG20(W)-VPN series firmware versions V5.10 through V5.38 could allow an attacker to download or upload files via a crafted URL.

    The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. The available sources name no fixed version. Check the vendor guidance in the references below. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Zyxel ATP series firmware eq versions V5.00 through V5.38..versions V5.00 through V5.38
    • Zyxel USG FLEX series firmware eq versions V5.00 through V5.38..versions V5.00 through V5.38
    • Zyxel USG FLEX 50(W) series firmware eq versions V5.10 through V5.38..versions V5.10 through V5.38
    • Zyxel USG20(W)-VPN series firmware eq versions V5.10 through V5.38..versions V5.10 through V5.38

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    7.5

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: NVD, CVSS v3

    7.5

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: pwn.watch, CVE.org

    2.9 %

    EPSS score

    Moderate — model estimates 1-10% exploitation likelihood.

    Source: FIRST EPSS, percentile 87.2

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    230.26 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    actively exploited
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    7.5 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    7.5
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

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    2.9 %
    Moderate — model estimates 1-10% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    87.2
    Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    Actively exploited
    Published
    In CISA KEV since

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    CISA assessment (SSVC)
    Exploitation: active · automatable · Technical impact: partial
    Source: CISA Vulnrichment, as of 5 December 2024
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-22

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This flaw is network-reachable without authentication and sits on the perimeter devices that provide internet access and remote VPN for many mid-market organisations. Attackers use it to pull configuration files containing credentials, then return through legitimate VPN access to move into the internal network. CISA explicitly flags known ransomware campaign use, which raises the impact ceiling to full-estate encryption. The exploitation likelihood is elevated. Treat any affected device with internet-exposed web management or SSL VPN as critical, and patch and rotate credentials within 24 h. Devices whose management is reachable only internally rank lower but still belong in the emergency patch cycle.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Inventory: Identify every Zyxel ATP, USG FLEX, USG FLEX 50(W) and USG20(W)-VPN appliance and check its firmware (GUI Dashboard or CLI show version). ZLD V5.00 through V5.38 are vulnerable, and V5.10 through V5.38 for USG FLEX 50(W) and USG20(W)-VPN.
      • Patch: Upgrade to firmware newer than V5.38. A patch is available from the vendor; look up the exact fixed version in the Zyxel security advisory for CVE-2024-11667. Download only from the official Zyxel portal and verify checksums.
      • Pull management off the internet: Immediately block HTTP/HTTPS access to the web management interface from the WAN zone by setting the WAN "To-Device" policy to deny. This typically covers TCP 443 and 80, plus any custom admin port such as 8443.
      • Rotate credentials: The flaw allows arbitrary file download, including configuration files that contain credential material. Rotate all local admin passwords, SSL VPN and IPsec user passwords, pre-shared keys and LDAP/RADIUS bind secrets. Do this even after patching.
      • Hunt for compromise: Review the user list for unknown admin or VPN accounts, and check for unexpected policies, NAT rules or forwarding entries. Disable suspicious accounts, and snapshot the config and logs before you clean anything up.
      • Escalate: If you find evidence of unauthorised access, trigger your IR process. Ransomware use is confirmed for this CVE, so hunt for lateral movement from the VPN address pool into internal networks. Assess your NIS2 reporting obligations, including the 24 h early warning.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: Restrict management to a dedicated management VLAN or a jump host. Limit LAN-zone "To-Device" rules to admin subnets, and avoid routing the VPN pool wholesale into server segments.
      • Upstream IPS/WAF: If a sensor sits in front of the firewall, block requests to the device IP that contain traversal sequences in the URI: ../, ..%2f, %2e%2e%2f, %252e%252e and ..\. Example Suricata shape: alert http any any -> $ZYXEL_MGMT any (msg:"Possible CVE-2024-11667 traversal"; http.uri; pcre:"/(\.\.|%2e%2e|%252e%252e)(\/|%2f|%5c)/i"; sid:9241166; rev:1;).
      • Source restriction: If SSL VPN must stay internet-facing, constrain source IPs with Geo-IP or allowlist objects. Also enable a lockout policy for failed logins.
      • IAM/least privilege: Enforce MFA (TOTP/2FA) for admin and VPN logins. Replace or rename default admin accounts. Split admin roles so that operations and monitoring use separate, least-privilege accounts.
      • Configuration hardening: Disable unneeded services on the WAN zone (HTTP, SSH, FTP, SNMP). Enable syslog forwarding to the SIEM so evidence survives on-box tampering.

    3. Runbook step 3

      Detection rules

      • Web/proxy and network telemetry (Zeek http.log, Suricata): Look for traversal patterns in requests to the management IP. Example SPL: index=netfw dest_ip IN ($zyxel_ips) uri="*..*" (uri="*%2e*" OR uri="*../*" OR uri="*%2f*") | stats count by src_ip, uri.
      • Zyxel syslog (System/User/Account categories): Watch for admin logins from unknown or external IPs, creation of new user or admin accounts, config changes outside change windows, and firmware or file uploads. Sigma shape: logsource: product: zyxel with selection: msg|contains: ['has been added', 'logged in'] and src_ip not in admin_nets.
      • VPN telemetry: Flag SSL VPN or IPsec sessions that use freshly created accounts or come from unusual geolocations. Use Zeek conn.log and firewall logs to spot VPN-pool IPs scanning SMB (445), RDP (3389), LDAP (389/636) or WinRM (5985/5986) internally.
      • Endpoint/AD (Windows Security log): Look for Event IDs 4624 (logon type 3/10) and 4625 from VPN-pool addresses, and 4720 and 4732 for new accounts or group changes. Also watch Sysmon EID 1 for vssadmin delete shadows and wbadmin as ransomware precursors. Example KQL: SecurityEvent | where EventID in (4624,4625) and IpAddress startswith "<VPN-pool>" | summarize count() by Account, IpAddress.
      • Egress from the appliance itself: Investigate unexpected outbound connections from the firewall's own IP to hosts other than Zyxel update or licensing servers. These may indicate exfiltration or payload staging.

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    A directory traversal vulnerability in the web management interface of Zyxel ATP series firmware versions V5.00 through V5.38, USG FLEX series firmware versions V5.00 through V5.38, USG FLEX 50(W) series firmware versions V5.10 through V5.38, and USG20(W)-VPN series firmware versions V5.10 through V5.38 could allow an attacker to download or upload files via a crafted URL.

    Source: pwn.watch, CISA KEV Catalog, cvelistv5, NVD (NIST), CVE.org (MITRE)

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    ZyxelATP series firmware
    • versions V5.00 through V5.38
    • —
    ZyxelUSG FLEX 50(W) series firmware
    • versions V5.10 through V5.38
    • —
    ZyxelUSG FLEX series firmware
    • versions V5.00 through V5.38
    • —
    ZyxelUSG20(W)-VPN series firmware
    • versions V5.10 through V5.38
    • —

    Vendors and products

    Affected operating systems

    Affected operating systems
    Otherzyxelzld—

    Weakness classes (CWE)

    • CWE-22Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

      Base

      The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.

      Entry at MITRE CWE-22

    Public exploit references

    Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

    Public exploit references
    CISA KEV CatalogCISA Known Exploited Vulnerability (opens in a new tab)cisa.govactively exploited

    References & sources

    • zyxel.comglobal/en/support/security-advisories/zyxel-security-advisory-p…Vendor advisory
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2024-11667government-resource
    • pwn.watchpwn.watch: Zyxel Multiple Firewalls Path Traversalpwn-watch
    • zyxel.comZyxel advisory: CVE-2024-11667pwn-watch
    • NVD (NIST)NVD: CVE-2024-11667pwn-watch
    • cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch
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