Security Vulnerability: SADDNS attack (CVE-2020-25705)

This document (000019786) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server 15
SUSE Linux Enterprise Server 12
 

Situation

Security researchers from University of California and Tsinghua University have identified a new variant of DNS cache poisoning attacks called SADDNS ("Side-channel AttackeD DNS") due to newly identified side channel attack against ICMP replies.

As DNS is UDP based, it is open to malicious package injection attacks, and various have been identified over time.

The DNSSSEC enhancement would fix the package injection attacks using cryptographic integrity protection, but is not yet widely deployed.

When using traditional DNS there have been 2 primary mitigations against this kind of poisoning been added:
  • randomization of the transaction ID (a 16 bit identity in every DNS packet)
  • randomization of the UDP port sending/receiving the replies (another 16 bit entity)
making it a 32bit wide space to exhaust for brute force attacks.

The researchers have now shown that the current Linux kernels have a side-channel attack using predictable ICMP port-unreachable replies on non-open UDP ports, like e.g. DNS reply ports, which allows attackers to remotely detect the open ports.

This again reduce the attack surface to 16 bit space, making DNS cache poisoning attacks again possible.

To restore the mitigation the solution is to remove this side channel attack from the Linux kernel.
 

Resolution

Implement Domain Name Security (DNSSEC). SUSE recommends a wider adoption and implementation of DNSSEC.

SUSE is also releasing kernel updates that removes the side-channel attack from the ICMP replies.
 

Workaround

  • Filter out "icmp type port-unreachable" messages on ipv4 and ipv6 via the firewall on your resolver host.
Sample iptables rules:
iptables -A OUTPUT -p icmp --icmp-type port-unreachable -j DROP
ip6tables -A OUTPUT -p ipv6-icmp --icmp-type port-unreachable -j DROP
This might however restrict network functionality.

Cause

Status

Security Alert

Additional Information

Disclaimer

This Support Knowledgebase provides a valuable tool for SUSE customers and parties interested in our products and solutions to acquire information, ideas and learn from one another. Materials are provided for informational, personal or non-commercial use within your organization and are presented "AS IS" WITHOUT WARRANTY OF ANY KIND.

  • Document ID:000019786
  • Creation Date: 16-Nov-2020
  • Modified Date:16-Nov-2020
    • SUSE Linux Enterprise Server

< Back to Support Search

For questions or concerns with the SUSE Knowledgebase please contact: tidfeedback@suse.com

SUSE Support Forums

Get your questions answered by experienced Sys Ops or interact with other SUSE community experts.

Join Our Community

Support Resources

Learn how to get the most from the technical support you receive with your SUSE Subscription, Premium Support, Academic Program, or Partner Program.


SUSE Customer Support Quick Reference Guide SUSE Technical Support Handbook Update Advisories
Support FAQ

Open an Incident

Open an incident with SUSE Technical Support, manage your subscriptions, download patches, or manage user access.

Go to Customer Center