Avahi avahi-daemon mDNS Response Traffic Amplification Denial of Service Vulnerability [CVE-2017-6519]

CVE Number – CVE-2017-6519

A vulnerability in the avahi-daemon component of Avahi could allow an unauthenticated, remote attacker to access sensitive information on a targeted system or conduct an amplified distributed denial of service (DDoS) attack against other targeted networks.

The vulnerability exists because the affected software misses link-local checks, causing the multicast DNS (mDNS) protocol to respond to IPv6 unicast queries with source addresses that are not on-link. An attacker could exploit this vulnerability by sending UDP port 5353 packets that submit malicious input to the targeted system. An exploit could allow the attacker to access sensitive system information (for example: model number, device type or operating system) or amplify DDoS attacks against other targeted networks. 

Avahi has confirmed the vulnerability and released software updates.


  • A successful exploit of this vulnerability can be used to amplify DDoS attacks against networks outside of the targeted system. Administrators may consider blocking UDP port 5353 traffic from entering or exiting their trusted internal network or disabling mDNS services.


  • Administrators are advised to apply the appropriate updates.

    Administrators are advised to allow only trusted users to have network access.

    Administrators are advised to run both firewall and antivirus applications to minimize the potential of inbound and outbound threats.

    Administrators may consider using IP-based access control lists (ACLs) to allow only trusted systems to access the affected systems.

    Administrators can help protect affected systems from external attacks by using a solid firewall strategy.

    Administrators are advised to monitor affected systems.

Vendor Announcements

  • Avahi has released an issue report at the following link: Issue #203

Fixed Software

Duncan Newell

Duncan is a technology professional with over 20 years experience of working in various IT roles. He has a interest in cyber security, and has a wide range of other skills in radio, electronics and telecommunications.

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