Tuesday, September 28, 2010

Securing HP Procurve Switches (or how to placate Auditors)

I was recently approached by an organization who suffered through an IT Systems and Security Audit.  Needless to say the audited highlighted a couple of holes in their system, and I was tasked with implementing the audit recommendations.  Part of my scope of work included securing their HP Procurve switches, this post will outline a couple of best-practices when securing your network equipment.  It is by no means exhaustive, but it should provide you with a good baseline.  All instructions assume you're logged into the switch and at the (config)# prompt

Defaults Configurations and Secure Alternatives

Telnet vs SSH
Telnet is an antiquated and insecure protocol; it sends all traffic across the wire in clear text. This includes user
names and passwords. Any attacker may eavesdrop on a Telnet session and obtain credentials.  Below are the commands detailing how to disable Telnet and and implement SSH.
  1. crypto key generate ssh
  2. ip ssh
  3. no telnet-server
ProCurve switches and routers can, by default, be configured through the web interface. The HTTP
interface has the same limitations as Telnet. It is therefore recommended that the HTTPS interface be configured and the HTTP interface be disabled, like so:
  1. crypto key generate cert 1024
  2. web-management ssl
  3. no web-management plaintext
TFTP client and server should be disabled as they do not require any authentication. Secure File
Transfer Protocol (SFTP) and Secure Copy Protocol (SCP) are part of the SSH protocol suite. As such provide an encrypted session using public/private keys between client and server just like
SSH.  You configure it like so:
  1. crypto key generate ssh
  2. ip ssh filetransfer 
  3. no tftp server
  4. no tftp client
SNMPv1/2c vs. SNMPv3
SNMP version 2 is enabled by default.  SNMPv2 community names are sent across the network as clear text (similiar to Telnet).  SNMP version 3 overcomes these weaknesses via encryption.  Here's how to configure it:
  1. snmpv3 enable
  2. snmpv3 only
If, for whatever reason, you cannot run SNMP v3, it is possible to run SNMP v2 in restricted mode, i.e. provide Read-Only access to your switch:
  1. snmp-server community restricted 
It is also possible to completely disable SNMP altogether:
  1. no snmp-server enable
Authorised IP Managers
It’s possible to restrict IP access to the switch to certain management IP's only.  This is configured via the following command:
  1. ip authorized-manager <IP address> mask  
Whilst not the be-all and end-all of security, the above should go a long way to ensure a reasonably secure base line for your HP Procurve network equipment.

Tuesday, September 14, 2010

Exchange 2010 ActiveSync Issue (or the dreaded HTTP Error 500)

Exchange ActiveSync (EAS for us smart people) is a pretty rocking way to get Smart phones hooked up to your Exchange Server.  9 times out of ten it "just works" if you follow the docs, but sometimes it doesn't.  Otherwise I wouldn't writing about it now, would I?

I had a rather perplexing case where EAS only worked for some users.  On the non-working users the only error message displayed was the rather unhelpful HTTP Error 500.  The only suggestion the usually excellent www.testexchangeconnectivity.com could offer was an old article applicable to Exchange 2003.


The next step was to scour the Application log on the Exchange Server, and lo and behold, the following error was logged:

Source: MSExchange ActiveSync
Event ID: 1053
Level: Error

Exchange ActiveSync doesn't have sufficient permissions to create the "CN=User Name,OU=Admins,OU=Employees,OU=People,DC=domain,DC=local" container under Active Directory user "Active Directory operation failed on server01.domain.local. This error is not retriable. Additional information: Access is denied.
Active directory response: 00000005: SecErr: DSID-031521D0, problem 4003 (INSUFF_ACCESS_RIGHTS), data 0
Make sure the user has inherited permission granted to domain\Exchange Servers to allow List, Create child, Delete child of object type "msExchangeActiveSyncDevices" and doesn't have any deny permissions that block such operations.

Righto.  So it would appear that to actually use EAS, information has to be written to the user account and to do this the Exchange Servers group needs to have permissions to the user object.  Further investigation revealed that the only accounts giving the error was Admin accounts.

AdminSDHolder and SDPROP are the culprits

Because the failing accounts has domain admins rights their User Object permissions were being reset by
AdminSDHolder, via a process called SDPROP.  I quote "Each Active Directory domain has an object called AdminSDHolder, which resides in the System container of the domain. The AdminSDHolder object has a unique Access Control List (ACL), which is used to control the permissions of security principals that are members of built-in privileged Active Directory groups (what I like to call "protected" groups). Every hour, a background process runs on the domain controller that holds the PDC Emulator operations master role. It compares the ACL on all security principals (users, groups and computer accounts) that belong to protected groups against the ACL on the AdminSDHolder object. If the size or the binary string is different, the security descriptor on the object is overwritten by the security descriptor from the AdminSDHolder object.."


Because SDPROP runs every hour, the fix needs to be applied and a EAS sync done before an hour has gone past.  Here is how:
  1. Launch the EMC from your Exchange CAS Server
  2. Browse to Server Configuration and select your server
  3. Go to the System Settings tab to see which Domain Controller is in use
  4. Launch ADUC from the DC located in step 3 and make sure Advanced View is enabled
  5. Right-click the user account and go to Properties
  6. Click the Security tab, then click Advanced
  7. Check the Include inheritable permission.... checkbox
  8. OK out of all the dialog boxes
  9. Sync your device
The sync should be successful, providing not more than an hour has passed between the sync and step 1.  Whilst this has been a very difficult issue to nail down, there is a lesson in there somewhere...DON'T USE PRIVILEGED ACCOUNTS FOR DAY-TO-DAY USE!!!