CriticalCVE-2020-29583

    Zyxel Multiple Products Use of Hard-Coded Credentials Vulnerability (CVE-2020-29583)

    Published In CISA KEV since Sources: CVE.org

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    What is affected, what to do

    Firmware version 4.60 of Zyxel USG devices contains an undocumented account (zyfwp) with an unchangeable password. The password for this account can be found in cleartext in the firmware.

    The vulnerability is being actively exploited; treat it as a priority. 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 Usg20-vpn Firmware eq 4.60..4.60
    • Zyxel Usg20w-vpn Firmware eq 4.60..4.60
    • Zyxel Usg40 Firmware eq 4.60..4.60
    • Zyxel Usg40w Firmware eq 4.60..4.60
    • Zyxel Usg60 Firmware eq 4.60..4.60
    • Zyxel Usg60w Firmware eq 4.60..4.60
    • Zyxel USG110 Firmware 4.33 (AAPH.0)C0 eq 4.60..4.60
    • Zyxel USG210 Firmware 4.33 (AAPI.0)C0 eq 4.60..4.60
    • Zyxel USG310 Firmware 4.33 (AAPJ.0)C0 eq 4.60..4.60
    • Zyxel USG1100 Firmware 4.33 (AAPK.0)C0 eq 4.60..4.60
    • Zyxel USG1900 Firmware eq 4.60..4.60
    • Zyxel Usg2200 Firmware eq 4.60..4.60
    • Zyxel Zywall110 Firmware eq 4.60..4.60
    • Zyxel Zywall310 Firmware eq 4.60..4.60
    • Zyxel Zywall1100 Firmware eq 4.60..4.60
    • Zyxel Atp100 Firmware eq 4.60..4.60
    • Zyxel Atp100w Firmware eq 4.60..4.60
    • Zyxel Atp200 Firmware eq 4.60..4.60
    • Zyxel Atp500 Firmware eq 4.60..4.60
    • Zyxel Atp700 Firmware eq 4.60..4.60
    • Zyxel Atp800 Firmware eq 4.60..4.60
    • Zyxel Vpn50 Firmware eq 4.60..4.60
    • Zyxel Vpn100 Firmware eq 4.60..4.60
    • Zyxel Vpn300 Firmware eq 4.60..4.60
    • Zyxel Vpn1000 Firmware eq 4.60..4.60
    • Zyxel Usg Flex 100 Firmware eq 4.60..4.60
    • Zyxel Usg Flex 100w Firmware eq 4.60..4.60
    • Zyxel USG FLEX 200 firmware eq 4.60..4.60
    • Zyxel USG FLEX 500 firmware eq 4.60..4.60
    • Zyxel USG FLEX 700 firmware eq 4.60..4.60

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

    Metrics

    9.8

    Priority

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

    Source: NVD, CVSS v3

    9.8

    CVSS v3

    Severity Critical on the scale from 0 to 10.

    Source: CVE.org

    90.1 %

    EPSS score

    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.

    Source: FIRST EPSS, percentile 99.80

    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
    228.68 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
    9.8 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
    9.8
    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“.

    Read in glossary
    90.1 %
    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
    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
    99.80
    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: total
    Source: CISA Vulnrichment, as of 10 February 2025
    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-522

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This flaw is exploitable over the network with no authentication and trivial complexity. The password is public, and a single login yields full admin control of a perimeter device. That combination puts it among the CVEs most likely to be exploited. Attackers mass-scan for exposed Zyxel management interfaces and use the access to create VPN accounts for network entry, redirect traffic or establish a persistent foothold. Typical victims are SMEs and branch offices that standardise on Zyxel. CISA does not flag known ransomware use, but perimeter access of this kind is a common precursor to follow-on intrusions. Treat any affected unit with internet-facing admin services as a top-priority emergency. Units administered only internally remain high priority but can follow the emergency patch window.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Inventory: Identify every Zyxel firewall (ATP100/100W/200/500/700/800, USG110/1100 and other USG models, VM editions) and NXC2500/NXC5500 AP controllers, and record their firmware versions. NVD lists firmware 4.60 as affected. The vendor indicates further series (e.g. USG FLEX, VPN) may be in scope; confirm against the advisory.
      • Upgrade firmware: A patch is available from the vendor. Look up the fixed version in Zyxel's security advisory for CVE-2020-29583. NXC controllers have their own fixed build, also listed in the advisory.
      • Close management access now: Disable SSH (TCP/22) and the web admin interface (TCP/443 or TCP/80) on the WAN interface. Restrict access to a dedicated management VLAN or a single jump host. The "zyfwp" account cannot be changed or removed, so reachability is the only lever you have before patching.
      • Assume compromise if exposed: If admin services on 4.60 were reachable from the internet, treat the device as compromised. Export the config and diff it against a known-good baseline. Hunt for unknown admin or VPN users, new port forwards and new rules.
      • Rotate secrets: Replace every secret stored on the device: local admin accounts, IPsec PSKs, SSL-VPN user passwords, RADIUS/LDAP bind credentials and certificate private keys.
      • Check reporting obligations: If unauthorised access is confirmed, assess your NIS2/BSI notification duty. The early warning is due within 24 h.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: Management interfaces must only be reachable from an isolated admin network. An upstream ACL should permit TCP/22 and TCP/443 to the firewall management IP only from named admin source IPs, and drop and log everything else.
      • On-device hardening: In Service Control (System > WWW/SSH), explicitly deny the WAN zone and allow only LAN/management. Disable FTP (TCP/21) unless strictly required; the vendor used this account for AP firmware distribution.
      • AP controller isolation: Make NXC2500/NXC5500 reachable only from the wireless management VLAN. Block client-network traffic to the controller.
      • Upstream IPS: Enable SSH brute-force and scan signatures for firewall management IPs. Where TLS inspection sits in front of the admin GUI, block login POSTs carrying the username zyfwp.
      • Remote administration: Route remote administration through a separate MFA-protected VPN gateway, never through the affected device itself.
      • Log resilience: Forward device syslog to the SIEM in real time, so an attacker with admin rights cannot erase the evidence by wiping local logs.

    3. Runbook step 3

      Detection rules

      • Zyxel syslog: Any occurrence of "zyfwp" in login, authentication or config events is a high-severity hit. SPL: index=network sourcetype=zyxel* "zyfwp" | stats count by src_ip, host, msg
      • Account and config changes: Alert on new admin or VPN users, changed firewall/NAT rules or disabled logging, especially outside change windows. Sigma shape: logsource: product: zyxel; detection: keywords|contains: ['user added','admin','configuration changed']; condition: and not src_ip in admin_net
      • Zeek: In ssh.log, look for id.resp_h == <fw_mgmt_ip> and id.orig_h !in admin_subnets, prioritising auth_success == T.
      • Flow/firewall logs: Look for internet-sourced HTTPS sessions to the WAN address on the admin port, particularly from known scanning ASNs.
      • Post-exploitation: Watch for SSL-VPN or IPsec logins by newly created users, internal connections sourced from the firewall's own interfaces (pivoting), and outbound connections from the appliance to unfamiliar destinations.

    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

    Firmware version 4.60 of Zyxel USG devices contains an undocumented account (zyfwp) with an unchangeable password. The password for this account can be found in cleartext in the firmware. This account can be used by someone to login to the ssh server or web interface with admin privileges.

    Source: NVD (NIST), cvelistv5, CISA KEV Catalog

    Vendors and products

    Affected operating systems

    Affected operating systems
    Otherzyxelatp100_firmware4.60
    Otherzyxelatp100w_firmware4.60
    Otherzyxelatp200_firmware4.60
    Otherzyxelatp500_firmware4.60
    Otherzyxelatp700_firmware4.60
    Otherzyxelatp800_firmware4.60
    Otherzyxelusg1100_firmware4.60
    Otherzyxelusg110_firmware4.60
    Otherzyxelusg1900_firmware4.60
    Otherzyxelusg20-vpn_firmware4.60
    Otherzyxelusg20w-vpn_firmware4.60
    Otherzyxelusg210_firmware4.60
    Otherzyxelusg2200_firmware4.60
    Otherzyxelusg310_firmware4.60
    Otherzyxelusg40_firmware4.60
    Otherzyxelusg40w_firmware4.60
    Otherzyxelusg60_firmware4.60
    Otherzyxelusg60w_firmware4.60
    Otherzyxelusg_flex_100_firmware4.60
    Otherzyxelusg_flex_100w_firmware4.60
    Otherzyxelusg_flex_200_firmware4.60
    Otherzyxelusg_flex_500_firmware4.60
    Otherzyxelusg_flex_700_firmware4.60
    Otherzyxelvpn1000_firmware4.60

    Weakness classes (CWE)

    • CWE-522Insufficiently Protected Credentials

      Class

      The product transmits or stores authentication credentials, but it uses an insecure method that is susceptible to unauthorized interception and/or retrieval.

      Entry at MITRE CWE-522

    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.comsupport/security_advisories.shtmlVendor advisory
    • ftp.zyxel.comUSG40/firmware/USG40_4.60(AALA.1)C0_2.pdfBroken link
    • businessforum.zyxel.comdiscussion/5254/whats-new-for-zld4-60-patch-1-available-on-dec-…Release notes
    • businessforum.zyxel.comdiscussion/5252/zld-v4-60-revoke-and-wk48-firmware-releaseRelease notes
    • eyecontrol.nlblog/undocumented-user-account-in-zyxel-products.htmlBroken link, Third-party advisory
    • zyxel.comsupport/CVE-2020-29583.shtmlVendor advisory
    • secpod.comblog/a-secret-zyxel-firewall-and-ap-controllers-could-allow-for…Exploit, Third-party advisory
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2020-29583government-resource, US government resource
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