G CITRIXHACKIN

Citrix Presentation Server 4.5 New version is called XenApp/Server Common Deployments Nfuse classic CSG – Citrix Secure Gateway Citrix Components Server farm Citrix XML service ICA client device Nfuse Web server CSG – Citrix Secure Gateway STA – Secure Ticketing Authority

Different Interfaces Browser accessible Program neighbourhood Gateway for Citrix Conferencing Manager NFuse Classic

ICA Client Device NFuse Network BrowserICA Client Browser Enters Credentials Into NFuse Web Page NFuse Sends Credentials To XML Service To Validate If Valid, XML Service Retrieves Application List From Farm NFuse Displays Application List User Selects Application And Receives An ICA File ICA Client Loads ICA File And Connects To Citrix Farm ICA Client Doesn’t NEED NFuse To Connect To Server Farm

ICA Client Device NFuse Network BrowserICA Client XML Service Can Sit On Independent Web Server XML Service Can Sit On One Of The App Servers XML Service Can Sit On The Nfuse Server Holes In Firewall Please Common Basic Deployment For Remote Network Application Exposure

Citrix Secure Gateway ICA Client Device Browser ICA Client Browser Enters Credentials Into NFuse Web Page NFuse Sends Credentials To XML Service To Validate If Valid, XML Service Retrieves Application List From Farm User Selects Application And NFuse Requests Ticket From STA Ticket Returned To Browser As Part Of ICA File CSG Verifies Ticket Against STA If Verified Then Access Is Provided To Server Farm ICA File And Ticket Format Explained Later More Secure As Server Farm Not Exposed. Firewalls In Between Segments ICA Client Connects To CSG (SSL) And Sends Ticket

Places To Sniff ICA Client Device BrowserICA Client HTTP Traffic Between Browser And Nfuse Cleartext credentials posted to login form Web Cookie ICA file returned from NFuse USE HTTPS

Places To Sniff Cleartext XML contains ‘encoded’ credentials HTTP Traffic Between NFuse And XML Service a -> M E G B b -> M H G C c -> M G G D d -> M B G E e -> M A G F f -> M D G G g -> M C G H h -> M N G I i -> M M G J j -> M P G K k -> M O G L l -> M J G M m -> M I G N n -> M L G O o -> M K G P USE HTTPS USE SSLRelay Password tN B H E te N B H E L E B B tes N B H E L E B B M H G C testN B H E L E B B M H G C L D B G In deployments that do not support running the SSL Relay, run the NFuse Web server on your Citrix server

Places To Sniff ICA protocol is not encrypted by default ICA Client Device BrowserICA Client ICA Traffic From Client Or CSG USE SecureICA USE SSL/TLS USE SSLRelay

Connection Data Between ICA Client And Server.ini type layout Doesn’t contain clear text credentials ICA File Format [ApplicationServers] Calc= [Calc] Address = :1494 BrowserProtocol = HTTPonTCP ClearPassword = 0674F0F9BD3B0D Domain = \DB247117DF8EC22A InitialProgram = #calc SSLProxyHost = CSG Address Username = Whoami

Nfuse Ticket Apparently it has an expiry time XOR credentials and send to XML server Get Ticket in response Split ticket prepend \ and place into domain:password STA Ticketing Is not server authentication Places ticket in the address field of.ica file 40;STA47;AFA4ABD7741BB BAC6AB2BDAF4 If I can talk to the STA server I can create STA tickets Ticketing STA MACHINE UNIQUE TICKET ONLY ALLOW CONNECTIONS FROM TRUSTED MACHINES Uses pseudo-random number generation to produce a 16-byte hex string. For security reasons, Citrix does not disclose the exact steps used to produce this random sequence of characters

Shadowing Allows Snooping On Other Sessions On by default Prompts user Shadowing

NFuse Web Application Controls access to the Web Application Authentication

Citrix Server Farm Published application setting Controls access to the application Authentication

Anon001 – Anon014 Created upon install Password set on each use Anonymous Access Easy to use Used for ‘temporary’ application use Anonymous Accounts

Installed By Default On Port 80 ISAPI extension under IIS Can be set for different port Sensitive Operations Require Auth Unless turned off for smartcard passthru Used by Nfuse and PNAgent Validate Credentials STA Requests Server Enumeration Citrix XML Service

Brute Force Web Page Brute force the NFuse login page Brute Force ICA File Will attempt to connect to Citrix application server ActiveX and API makes this easy Ask The IMA Service Sits on UDP port 1604 Unauthenticated requests will respond with application list Ask The XML Service By default sits on TCP port 80 If you ask politely it tell you Gaining Access

Anonymous vs Standard Internal User Breaking The Citrix Sandbox Weak security settings Uploading Tools Alternative file transfer methods Privilege Escalation Third party or windows vulnerability Token Theft Full domain control Demonstration

No Citrix Vulnerability Exploited Weak / default configuration Anonymous Application Access Was only part of the issue Pretty Common Scenario Most citrix reviews involve gaining ‘shell’ access Recap

Lockdown Citrix Disable file sharing Enabled ‘run only published applications’ Turn on encryption and use SSL Lockdown OS Use group policy to enforce restrictions Disable the runas service Lockdown File System Restrict users access to directories and commands Understand The Weaknesses Hopefully this demonstration has helped Securing