Skip to main content

Securing HSRP


In previous post I went over attacking HSRP using default authentication of "cisco". In this post I'll go over defenses.

HSRP attacks are performed at Layer 2 so the attacker must be on the same L2 domain (same VLAN/subnet). Probably this is the reason no one pays much attention to it. "It's our LAN, it's behind firewall so it's safe. Right?" Maybe, but there are bored employees, there are misconfigurations, and there could be malware that would mess up your network.

Either way, if it can be more secure it should be. That's what "defense-in-depth" is all about.

HSRP supports authentication. Either a plain-text or md5 ca be used. Plain text option provides little to no protection as the plain text password is sent in clear text with every HSRP packet. MD5 authentication solves the problem. It uses a secret key to generate a keyed MD5 hash of the packet that is part of the outgoing packet. A keyed hash of an incoming packet is generated and if the generated hash does not match the hash within the incoming packet, the packet is ignored.

To enable MD5 authentication the following command is used in the interface configuration context:

R1(config-if) #standby authentication md5 key-string "the key"



HSRP packet with default authentication:


HSRP packet with md5 authentication enabled:


Labels:

Comments

Post a Comment

Popular posts from this blog

x.509 Certificates - Critical vs non-critical extensions

Extensions are used to associate additional information with the user or the key.  Each certificate extension has three attributes - extnID, critical, extnValue extnID - Extension ID - an OID that specifies the format and definitions of the extension critical - Critical flag - Boolean value extnValue - Extension value  Criticality flag specifies whether the information in an extension is important. If an application doesn't recognize the extension marked as critical, the certificate cannot be accepted. If an extension is not marked as critical (critical value False) it can be ignored by an application. In Windows, critical extensions are marked with a yellow exclamation mark,  View certificate extensions using OpenSSL: # openssl x509 -inform pem -in cert.pem -text -noout (output abbreviated)         X509v3 extensions:             X509v3 Key Usage: critical                 Digital Signature, Key Encipherment             X509v3 Subject Key Identifier
Post a Comment
Read more

DNS response and error types

In this post we explore common DNS response codes. We will cover the following responses: NOERROR SERVFAIL NXDOMAIN NODATA REFUSED Throughout article we’ll refer to the following RFCs: RFC 1034 - DOMAIN NAMES - CONCEPTS AND FACILITIES RFC 2308 - Negative Caching of DNS Queries (DNS NCACHE) RFC 2136 - Dynamic Updates in the Domain Name System (DNS UPDATE) RFC 8914 - Extended DNS Errors Response Codes - RCODEs The DNS RCODES are best defined in RFC2316 .  They signify what type of response was sent by the server. “RCODE   Response code - this four bit field is undefined in requests and set in responses.”   The table below shows the summary of the currently defined RCODEs. Mnemonic Val Description NOERROR 0 No error condition.
Post a Comment
Read more

DNS blocking in Indonesia

DNS based censorship and domain blocking in Indonesia is very inconsistent among ISPs. There’s a government mandated black list which the ISPs operating in the country should enforce. However, Indonesia lacks centralised internet infrastructure and has many separate ISPs. In addition, the Indonesian government granted ISPs the authority to block content at their own discretion. All of this leads to a very inconsistent DNS blocking in Indonesia. Official DNS domain blacklist in Indonesia The Government mandated DNS blacklist is published in a redacted form and can be downloaded here: https://trustpositif.kominfo.go.id/ . This is where the blocked domains get redirected to. We can search the database and check if a domain is blocked. In the screenshot below we can see that a popular cryptocurrency exchange is blocked (Ada) and that wikipedia.org is not (Tidak Ada) - thanks to Google Translate. Examples of blocked DNS queries dig binance.com @182.253.45.122 ;; global options: +cmd ;; Got
Post a Comment
Read more