Just a quick glance at the domain_analyzer script from Sebastián García and Verónica Valeros. “Domain analyzer is a security analysis tool which automatically discovers and reports information about the given domain. Its main purpose is to analyze domains in an unattended way.” Nice one. If you’re running your own DNS servers you should check e.g. whether your firewall rules are correct (scanned with Nmap) or whether you’re not allowing zone transfer, etc.
Category Archives: DNS/DNSSEC
DNS Test Names & Resource Records
I am testing a lot with my own DNS servers as well as with third-party DNS implementations such as DNS proxies on firewalls, DNSSEC validation on resolvers, etc. While there are a number of free DNS online tools around the Internet I was lacking some DNS test names with certain properties or resource records. Hence I configured a couple of them on my own authoritative DNS servers and its zone weberdns.de.
For example, we encountered a bug on the Palo Alto DNS proxy that has not stored the TTL value correctly – hence some test names with different TTL values. Or we had some problems when a single DNS name has more than 15 IPv4/IPv6 addresses – hence some test names with lots of addresses. And many more: Continue reading DNS Test Names & Resource Records
PGP Key Distribution via DNSSEC: OPENPGPKEY
What is the biggest problem of PGP? The key distribution. This is well-known and not new at all. What is new is the OPENPGPKEY DNS resource record that delivers PGP public keys for mail addresses. If signed and verified with DNSSEC a mail sender can get the correct public key for his recipient. This solves both key distribution problems: 1) the delivery of the public key and 2) the authenticity of the key itself, i.e., that you’re using the correct key to encrypt a mail.
The “DNS-Based Authentication of Named Entities (DANE) Bindings for OpenPGP” is specified in the experimental RFC 7929. Let’s have a look on how you can add your public key into the zone file of your DNS server.
Continue reading PGP Key Distribution via DNSSEC: OPENPGPKEY
CAA: DNS Certification Authority Authorization
I really like the kind of security features that are easy to use. The CAA “DNS Certification Authority Authorization” is one of those, specified in RFC 6844. As a domain administrator you must only generate the appropriate CAA records and you’re done. (Unlike other security features such as HPKP that requires deep and careful planning or DANE which is not used widely.) Since the check of CAA records is mandatory for CAs since 8. September 2017, the usage of those records is quite useful because it adds another layer of security.
Continue reading CAA: DNS Certification Authority Authorization
PAN NGFW IPv6 NDP RA RDNSS & DNSSL
Haha, do you like acronyms as much as I do? This article is about the feature from Palo Alto Networks’ Next-Generation Firewall for Internet Protocol version 6 Neighbor Discovery Protocol Router Advertisements with Recursive Domain Name System Server and Domain Name System Search List options. ;) I am showing how to use it and how Windows and Linux react on it.
BIND Inline-Signing Serial Numbers Cruncher
I know that BIND correctly changes the serial numbers of zones when it is enabled with inline signing and auto-dnssec. However, I got confused one more time as I looked on some of my SOA records. So, just for the record, here is an example how the serial numbers increase while the admin has not changed anything manually on the zone files.
Continue reading BIND Inline-Signing Serial Numbers Cruncher
Idea: SSHFP Validator
The usage of the SSHFP resource record helps admins to authenticate the SSH server before they are exposing their credentials or before a man-in-the-middle attack occurs. This is only one great extension of DNSSEC (beside DANE whose TLSA records can be used to authenticate HTTPS/SMTPS servers).
While there are some great online tools for checking the mere DNS (1, 2), the correct DNSSEC signing (3, 4), or the placement of TLSA resource records for DANE (5, 6, 7), I have not found an online SSHFP validator. That’s the idea:
Idea: On-the-Fly TLSA Record Spoofing
It is quite common that organizations use some kind of TLS decryption to have a look at the client traffic in order to protect against malware or evasion. (Some synonyms are SSL/TLS interception, decryption, visibility, man-in-the-middle, …) Next-generation firewalls as well as proxies implement such techniques, e.g., Palo Alto Networks or Blue Coat. To omit the certificate warnings by the clients, all spoofed certificates are signed by an internal root CA that is known to all internal clients. For example, the root CA is published via group policies to all end nodes.
But what happens if the DNS-based Authentication of Named Entities (DANE) is widely used within browsers? From the CA perspective, the spoofed certificates are valid, but not from the DANE perspective. To my mind we need something like an on-the-fly TLSA record spoofing technique that works in conjunction with TLS decryption.
Detect DNS Spoofing: dnstraceroute
Another great tool from Babak Farrokhi is dnstraceroute. It is part of the DNSDiag toolkit from which I already showed the dnsping feature. With dnstraceroute you can verify whether a DNS request is indeed answered by the correct DNS server destination or whether a man-in-the-middle has spoofed/hijacked the DNS reply. It works by using the traceroute trick by incrementing the TTL value within the IP header from 1 to 30.
Beside detecting malicious DNS spoofing attacks, it can also be used to verify security features such as DNS sinkholing. I am showing the usage as well as a test case for verifying a sinkhole feature.
Compare & Troubleshoot DNS Servers: dnseval
The third tool out of the DNSDiag toolkit from Babak is dnseval. “dnseval is a bulk ping utility that sends an arbitrary DNS query to a given list of DNS servers. This script is meant for comparing response times of multiple DNS servers at once”. It is not only listing the response times but also further information about the DNS responses such as the TTL and the flags. Really great for comparison and troubleshooting different DNS forwarders as well as own authoritative DNS server responses as seen by others.
Continue reading Compare & Troubleshoot DNS Servers: dnseval
How to walk DNSSEC Zones: dnsrecon
After the implementation of DNS and DNSSEC (see the last posts) it is good to do some reconnaissance attacks against the own DNS servers. Especially to see the NSEC or NSEC3 differences, i.e., whether zone walking (enumeration) is feasible or not.
For many different kinds of DNS reconnaissance the tool dnsrecon can be used. In this post I will focus on the -z option which is used for DNSSEC zone walking, i.e., walk leaf by leaf of the whole DNS zone.
DNSSEC with NSEC3
By default DNSSEC uses the next secure (NSEC) resource record “to provide authenticated denial of existence for DNS data”, RFC 4034. This feature creates a complete chain of all resource records of a complete zone. While it has its usage to prove that no entry exists between two other entries, it can be used to “walk” through a complete zone, known as zone enumeration. That is: an attacker can easily gather all information about a complete zone by just using the designed features of DNSSEC.
For this reason NSEC3 was introduced: It constructs a chain of hashed and not of plain text resource records (RFC 5155). With NSEC3 enabled it is not feasible anymore to enumerate the zone. The standard uses a hash function and adds the NSEC3PARAM resource record to the zone which provides some details such as the salt.
DNSSEC ZSK Key Rollover
One important maintenance requirement for DNSSEC is the key rollover of the zone signing key (ZSK). With this procedure a new public/private key pair is used for signing the resource records, of course without any problems for the end user, i.e., no falsified signatures, etc.
In fact it is really simply to rollover the ZSK with BIND. It is almost one single CLI command to generate a new key with certain time ranges. BIND will use the correct keys at the appropriate time automatically. Here we go:
SSHFP: Authenticate SSH Fingerprints via DNSSEC
This is really cool. After DNSSEC is used to sign a complete zone, SSH connections can be authenticated via checking the SSH fingerprint against the SSHFP resource record on the DNS server. With this way, administrators will never get the well-known “The authenticity of host ‘xyz’ can’t be established.” message again. Here we go:
Continue reading SSHFP: Authenticate SSH Fingerprints via DNSSEC
How to use DANE/TLSA
DNS-based Authentication of Named Entities (DANE) is a great feature that uses the advantages of a DNSSEC signed zone in order to tell the client which TLS certificate he has to expect when connecting to a secure destination over HTTPS or SMTPS. Via a secure channel (DNSSEC) the client can request the public key of the server. This means, that a Man-in-the-Middle attack (MITM) with a spoofed certificate would be exposed directly, i.e., is not possible anymore. Furthermore, the trust to certificate authorities (CAs) is not needed anymore.
In this blog post I will show how to use DANE and its DNS records within an authoritative DNS server to provide enhanced security features for the public.