CriticalCVE-2020-8515

    Multiple DrayTek Vigor Routers Web Management Page Vulnerability (CVE-2020-8515)

    Published In CISA KEV since Sources: SingCERT, CVE.org

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    What is affected, what to do

    DrayTek Vigor2960 1.3.1_Beta, Vigor3900 1.4.4_Beta, and Vigor300B 1.3.3_Beta, 1.4.2.1_Beta, and 1.4.4_Beta devices allow remote code execution as root (without authentication) via shell metacharacters to the cgi-bin/mainfunction.cgi URI. This issue has been fixed in Vigor3900/2960/300B v1.5.1.

    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
    • DrayTek Vigor2960 Firmware eq 1.3.1..1.3.1
    • DrayTek Vigor300b Firmware eq 1.3.3..1.3.3
    • DrayTek Vigor300b Firmware eq 1.4.2.1..1.4.2.1
    • DrayTek Vigor300b Firmware eq 1.4.4..1.4.4
    • DrayTek Vigor3900 Firmware eq 1.4.4..1.4.4

    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: SingCERT, CVE.org

    99.99 %

    EPSS score

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

    Source: FIRST EPSS, percentile 99.99

    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
    228.98 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
    99.99 %
    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
    99.99
    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 4 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-78

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This flaw is network-reachable without authentication or user interaction and gives root code execution on a perimeter device, placing it among the CVEs most likely to be exploited. Since disclosure it has been hit by mass, automated scanning and botnet campaigns that turn routers into DDoS nodes, proxy infrastructure, traffic-interception points or footholds into the internal network. CISA does not flag known ransomware use, but an owned edge router exposes VPN and admin traffic and enables lateral movement. Treat any affected device with an internet-facing management page as critical and act now. Treat internally reachable units as high priority and patch them within days.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Inventory: Locate every DrayTek Vigor2960, Vigor3900 and Vigor300B, including branch offices and MSP-managed links, and record the firmware version. The advisory lists Vigor2960 1.3.1_Beta, Vigor3900 1.4.4_Beta and Vigor300B 1.3.3_Beta, 1.4.2.1_Beta and 1.4.4_Beta as affected. Treat older, unlisted builds as vulnerable too.
      • Patch: Upgrade to firmware v1.5.1 or later (Vigor3900/2960/300B). Check each device's support lifecycle with the vendor and schedule replacement for anything that no longer receives updates.
      • Pull the web UI off the WAN: Disable remote web management on the WAN interface immediately. This typically covers TCP 80/443, plus any custom ports such as 8080/8443. Allow management only from a dedicated admin network or over VPN.
      • Assume compromise if exposed: If the management page was internet-reachable before patching, treat the device as potentially owned. Exploitation is unauthenticated and yields root.
      • Rebuild compromised devices: Export the config and review it for tampering (users, port forwards, DNS servers, scheduled tasks, VPN profiles). Then factory-reset, reflash v1.5.1+, and restore a reviewed configuration.
      • Rotate secrets: Rotate everything stored on the box: admin passwords, VPN PSKs and certificates, RADIUS/LDAP bind credentials, and SNMP communities.

    2. Runbook step 2

      Mitigation layers

      • Segmentation: Make management interfaces reachable only from an isolated admin VLAN or jump host. Add upstream ACLs (ISP or perimeter firewall) that drop inbound traffic to the router's management ports on its WAN IP.
      • IPS/WAF: Block requests to /cgi-bin/mainfunction.cgi containing shell metacharacters. Watch for ;, |, backticks, $(, %0a, %27 and %3b, especially in the keyPath, rtick and loginUser parameters with action=login. Enable the public ET Suricata/Snort signatures for CVE-2020-8515.
      • Egress filtering: Restrict router-originated traffic to the destinations it actually needs (NTP, DNS, vendor update servers). Block arbitrary HTTP/TFTP downloads and unusual destination ports, since payloads are typically fetched via wget/curl/tftp.
      • Access control: If remote management is unavoidable, restrict it with the management access control list to fixed source IPs. Disable unused services such as WAN-side Telnet/SSH and UPnP.
      • Lifecycle risk: Under NIS2, unsupported perimeter devices are an unmanageable risk. Document a formal exception and set a migration deadline.

    3. Runbook step 3

      Detection rules

      • Web/proxy/WAF logs: Flag requests to mainfunction.cgi that carry metacharacters. SPL sketch: index=proxy uri_path="*/cgi-bin/mainfunction.cgi*" (form_data="*keyPath=*%27*" OR form_data="*rtick=*" OR form_data="*;*" OR form_data="*%0a*")
      • Network telemetry (Suricata/Zeek): Watch for internet-sourced POSTs to /cgi-bin/mainfunction.cgi in http.log. Sigma shape: cs-uri-stem|endswith: '/cgi-bin/mainfunction.cgi' AND cs-body|contains: ['wget','curl','tftp','busybox','/tmp/','chmod'].
      • Router-originated traffic: In Zeek conn.log, alert on connections sourced from the router's own IP to unknown external hosts, such as HTTP GETs for ELF binaries or IRC/non-standard ports. Outbound scanning from the router (mass SYNs to 23/TCP or 80/TCP) indicates botnet enrolment.
      • Router syslog: Forward syslog to the SIEM and alert on unexpected config changes, new admin accounts, reboots, changed DNS servers or new port forwards.
      • External view: Regularly scan your public ranges, or check attack-surface feeds, for exposed DrayTek management pages. Every hit becomes an incident ticket.

    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

    DrayTek Vigor2960 1.3.1_Beta, Vigor3900 1.4.4_Beta, and Vigor300B 1.3.3_Beta, 1.4.2.1_Beta, and 1.4.4_Beta devices allow remote code execution as root (without authentication) via shell metacharacters to the cgi-bin/mainfunction.cgi URI. This issue has been fixed in Vigor3900/2960/300B v1.5.1.

    Source: CSA/SingCERT, NVD (NIST), cvelistv5, CISA KEV Catalog

    Vendors and products

    Affected operating systems

    Affected operating systems
    Otherdraytekvigor2960_firmware1.3.1
    Otherdraytekvigor300b_firmware1.3.3
    Otherdraytekvigor300b_firmware1.4.2.1
    Otherdraytekvigor300b_firmware1.4.4
    Otherdraytekvigor3900_firmware1.4.4

    Weakness classes (CWE)

    • CWE-78Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')

      Base

      The product constructs all or part of an OS command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended OS command when it is sent to a downstream component.

      Entry at MITRE CWE-78

    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
    Packet StormDrayTek Vigor2960 Vigor3900 Vigor300B Remote Command Execution (opens in a new tab)packetstormsecurity.comPoC (publicly reported)reported, not verified—

    References & sources

    • sku11army.blogspot.com2020/01/draytek-unauthenticated-rce-in-draytek.htmlx_refsource_MISC, Permissions required, Third-party advisory
    • draytek.comabout/security-advisory/vigor3900-/-vigor2960-/-vigor300b-route…x_refsource_MISC, Vendor advisory
    • packetstormsecurity.comfiles/156979/DrayTek-Vigor2960-Vigor3900-Vigor300B-Remote-Comma…x_refsource_MISC, Exploit, Third-party advisory, Vulnerability database
    • cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2020-8515government-resource, US government resource

    Linked advisories

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    Badge preview for CVE-2020-8515
    <a href="https://intel.neosec.eu/en/cve/CVE-2020-8515"><img src="https://intel.neosec.eu/badge/cve/CVE-2020-8515.svg?lang=en" alt="CVE-2020-8515 – NEOSEC Intel" height="20"></a>