CriticalCVE-2018-10561

    Dasan GPON Routers Authentication Bypass Vulnerability (CVE-2018-10561)

    Published In CISA KEV since Sources: CVE.org

    What is affected, what to do

    An issue was discovered on Dasan GPON home routers. It is possible to bypass authentication simply by appending "?images" to any URL of the device that requires authentication, as demonstrated by the /menu.html?images/ or /GponForm/diag_FORM?images/ URI.

    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.

    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

    92.8 %

    EPSS score

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

    Source: FIRST EPSS, percentile 99.83

    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
    228.73 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.

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    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.

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    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“.

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    92.8 %
    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.

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    99.83
    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.

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    Response and mitigation

    Why act now?

    Prioritisation rationale

    This flaw is network-reachable without authentication or user interaction. Chained with CVE-2018-10562, it gives trivial full device takeover. It sits among the CVEs most likely to be exploited, and IoT botnets have abused it automatically for years for DDoS, proxying and self-propagation. CISA does not list known ransomware use. For organisations, the exposure lives mainly in branch and home-office links on ISP-supplied CPE, where a hijacked router enables DNS tampering, traffic interception and abuse of your IP reputation. Treat it as top priority wherever an affected unit exposes its web UI to the internet. Where no such devices exist, perimeter monitoring of the scan traffic is sufficient.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Inventory: Identify every Dasan GPON ONT/router you are responsible for, including branch offices, remote-worker connections and ISP-supplied CPE. Fingerprint on the HTTP paths /menu.html and /GponForm/ and the web UI server header. Scan internally on ports 80/8080/443/8443.
      • Kill WAN-side management now: Disable remote access to the web interface from the internet. Where the device does not allow this, block the management ports at an upstream firewall or via the ISP ACL.
      • Update firmware: A patch is available from the vendor — look up the fixed version in the Dasan Zhone vendor advisory or with your ISP. Most units are ISP-managed, so open a ticket with the provider referencing CVE-2018-10561 and CVE-2018-10562.
      • Assume compromise: Treat any unit whose web UI was internet-reachable as potentially compromised. Factory-reset it, flash patched firmware, then rotate all credentials (admin, Wi-Fi PSK, PPPoE/VoIP secrets).
      • Replace unpatchable or EoL units: Schedule replacement with current, provider-approved CPE. Until then, treat these devices as an untrusted zone.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: Run the GPON unit in bridge/modem mode only and place a managed firewall behind it. Tunnel corporate traffic from branches over IPsec/WireGuard so the router is reduced to transport.
      • Restrict management access: Allow the web UI only from a dedicated management VLAN or named admin IPs. Block client-LAN and WAN access to the router's ports 80/443/8080/8443.
      • WAF/IPS rule: On any upstream inspection point, drop HTTP requests whose URI contains ?images after an authenticated path, or that target /GponForm/diag_FORM. Suricata sketch: alert http any any -> $HOME_NET any (msg:"GPON auth bypass CVE-2018-10561"; http.uri; content:"/GponForm/"; content:"?images"; sid:9000001;).
      • Egress filtering: Limit outbound traffic from the router management IP to what it needs: NTP, DNS and the provider's TR-069 ACS. This breaks bot payload retrieval via wget/tftp.
      • Hardening: Disable unused services (Telnet, UPnP, TR-069 unless the ISP requires it) and set a strong unique admin password. The bypass sidesteps authentication, but this limits follow-on abuse once patched.

    3. Runbook step 3

      Detection rules

      • Web server/proxy logs: Hunt for ?images in URIs targeting /menu.html, /GponForm/diag_FORM or other protected paths. SPL: index=web uri="*?images*" (uri="*/GponForm/*" OR uri="*/menu.html*") | stats count by src_ip, dest_ip, uri.
      • Command injection pattern (CVE-2018-10562): Look for POST bodies containing XWebPageName=diag, diag_action=ping and dest_host= with backticks, ;, |, wget, curl, tftp or busybox. Sigma shape: cs-uri-stem|contains: '/GponForm/diag_FORM' AND cs-uri-query|contains: 'images'.
      • Network telemetry (Zeek/Suricata): Watch for HTTP/TFTP downloads of MIPS/ARM ELF binaries to the router. Also flag new outbound connections to odd ports (e.g. Telnet 23/2323) and scanning behaviour from the router IP against internal or external hosts. Zeek: files.log where mime_type == "application/x-executable" and the router IP is a party.
      • Perimeter view: Mass GPON exploit scans against your public IPs are background noise. A hit against an actual Dasan device that returns HTTP 200 needs escalation.
      • Config drift: Unexpected changes to DNS servers, port forwards or admin accounts on the router are a compromise indicator. Catch them with periodic config exports or with client DNS anomalies (Zeek dns.log: clients suddenly querying unfamiliar resolvers).

    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

    An issue was discovered on Dasan GPON home routers. It is possible to bypass authentication simply by appending "?images" to any URL of the device that requires authentication, as demonstrated by the /menu.html?images/ or /GponForm/diag_FORM?images/ URI. One can then manage the device.

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

    Vendors and products

    Affected operating systems

    Affected operating systems
    Otherdasannetworksgpon_router_firmware—

    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
    Exploit-DBEDB-ID 44576 (opens in a new tab)exploit-db.comPoC (publicly reported)reported, not verified—

    References & sources

    • securityfocus.com107053Vulnerability database, x_refsource_BID, Broken link, Third-party advisory, Vulnerability database
    • exploit-db.com44576Exploit, x_refsource_EXPLOIT-DB, Exploit, Third-party advisory, Vulnerability database
    • vpnmentor.comblog/critical-vulnerability-gpon-routerx_refsource_MISC, Exploit, Technical description, Third-party advisory
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2018-10561government-resource, US government resource
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