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Network Security

Network Security

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Network Security

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  1. Attack Analysis Network Security

  2. Outline • Types of Attacks • Vulnerabilities Exploited • Network Attack Phases • Attack Detection Tools

  3. Vulnerability Summary forWeek of April 29, 2013 • From US-CERT • • Ranks vulnerabilities based on CVSS score (common vulnerability scoring system) • High – base score of 10.0 – 7.0 • Medium – base score of 6.9 to 4.0 • Low – base score of 3.99 – 0.0

  4. CVSS scoring

  5. Vulnerability Summary forWeek of April 29, 2013 • High Vulnerabilities

  6. Vulnerability Summary forWeek of April 29, 2013 • Medium Vulnerabilities

  7. Vulnerability Summary forWeek of April 29, 2013 • Low Vulnerabilities


  9. Types of Attacks • Software vulnerabilities • Buffer overflows • Viruses, trojans, etc. • System or service configuration mistakes • Password weaknesses • Denial-of-Service attacks • Wireless Attacks

  10. Buffer Overflows • Objective: • Send more data to an application input than it is designed to handle. • Craft the data such that the overflow portion will be interpreted as executable code. • Typically done by getting data to overflow in stack so that it overwrites PC address • Depends on: • Traditional (non-checked) data validation. • Code instructions that do not validate input.

  11. Buffer Overflow Example void function(char *str) { char buffer[16]; strcpy(buffer,str); } void main() { char large_string[256]; int i; for( i = 0; i < 255; i++)‏ large_string[i] = 'A'; function(large_string); }

  12. Stack Structure for function bottom of top of memory memory codebuffer sfp ret *str <------ [XXXXXXXXXXXXXXXX][XXXX][XXXX][XXXX] top of bottom of stack stack *str pointer to char buffer (argument into function)‏ ret pointer to return address in main sfp saved frame pointer (reference into memory frame)‏ buffer Local storage allocated for character array code …

  13. Stack Overflow Before strcpy: bottom of top of memory memory buffer sfp ret *str <------ [XXXXXXXXXXXXXXXX][1F3C][1F9A][1F7C] top of bottom of stack stack After strcpy: bottom of top of memory memory buffer sfp ret *str <------ [AAAAAAAAAAAAAAAA][AAAA][AAAA][AAAA] top of bottom of stack stack

  14. Stack Manipulation bottom of top of memory memory buffer sfp ret *str <------ [AAAAAAAAAAAAAAAA][XXXX][1F94][XXXX] top of bottom of stack stack Overflow buffer with the bytes needed to overwrite the return pointer with a desired address That points to an instruction of your own crafting bottom of top of memory memory buffer sfp ret *str <------ [AAAAAAAAAAAAAAAA][XXXX][1F41][XXXX] top of bottom of stack stack

  15. Viruses, trojans, etc. • Check for evidence of programs (and versions) that are susceptible to attack. • Test for outdated (or unchecked) virus scan software.

  16. System or service configuration mistakes • Default passwords left in place • Router passwords • Program passwords • Default (unused) services left running • Sendmail • Echo, time, etc. • Default settings for firewalls and routers

  17. Password weaknesses • Test for standard password weaknesses • Short passwords • Dictionary based passwords • Personal information passwords (pets, family, etc.)‏ • Test for unencrypted passwords • Try to download encrypted password files • /etc/passwd, /etc/shadow • Use dictionary, etc as source • Encrypt word, compare to password file

  18. Wireless Attacks • Scan for Access Points (War Driving)‏ • Look for SSID beacons • Test for mac address blocking • Look for unencrypted access points • If encrypted, test for WEP / WPA / WPA2 • If WEP, consider the value of capturing data and trying to recover secret through IV

  19. Network Attack Phases • Reconnaissance • Vulnerability Identification • Penetration • Control • Embedding • Data extraction / modification • Attack Relay

  20. Reconnaissance • Find out about network topology • What IP addresses are active? • What Operating Systems do they use? • What services / servers do they support? • What other machines do they talk to? • Tools • Port Scanners • DNS queries (zone transfers)‏ • Defense • Snort, Shadow

  21. Vulnerability Identification • Once systems have been scanned, specific sweeps are made to check for specific service or system vulnerabilities • See SANS top 20 • Buffer overflows, etc. • Most Popular Targets • Servers difficult to remove or relocate ( DNS, mail, web, etc.)‏ • Defense • Don’t expose vulnerabilities!

  22. Penetration • Most sucessful hack is one that is not detected • Second best is an attack that cannot be traced. • Systems with some security typically rely on a “hard shell”. • Firewall or proxy servers • Perhaps IDS • If firewall is secure, then use the users • Track external site visits • Taint DNS records to point to an attack machine • Let users establish the connection for you!

  23. Control • Typically a bootstrap process. • Find an exploit that allows you to control a process (program). • Use that process to start up a process of your choosing with permissions of the owner of the original process • This process will contact the attack host and download the full exploit. • Use that process to execute another exploit that will get root privilege (if needed).

  24. Embedding • Once into the system, the hacker will attempt to hide several different access programs. • If one exploit is discovered, perhaps others will not. • Alter logging programs to not display packets • Alter process display programs to not show processes • Etc. • Want to be sure that the attack program (bot) will survive a restart.

  25. Embedding • Store exploits by overwriting little used existing files (games, etc.)‏ • Store most of the exploit as fragments inside other files (steganography), then use a small reassembly program to rebuild on command • Hide program on unused portions of the disk • Load portions of the bot onto unused eeprom on the network card.

  26. Data extraction / modification • First order of business is to send system data back to relay • Windows – registry • Linux - /proc • Transmit data slowly – over several different sessions • Encrypt and embed data into known (or expected) data flows – www, ftp, e-mail, etc. • Use existing programs RMON and arpwatch

  27. Attack Relay • Use this new system as a relay to attack other systems. • Use multiple relays – ideally in multiple countries – to link to attacked machines. • Use multiple machines for an attack • A few suspicious packets from a machine once in a week may not be acted upon • Multiple machines are harder to block.

  28. Attack Detection Tools • Scanners • Virus Scanners • SpyBots • Malware scanners • IDS • Network based • Host based

  29. Profile of an Advanced Cyber Intrusion • Ongoing (since 1999) series of suspected intrusions on US commercial and military sites from PRC • Information presented in an unclassified document that details China’s capability to conduct cyber attacks • One element of that report is a detailed report of an intrusion into a US commercial network

  30. Awareness of the Problem • Information security staff at the company became aware of the intrusion when they detected large volumes of data leaving their network • Coming from multiple machines • Going to multiple addresses mostly (completely?) within the US • Were able to implement blocks to stop the flow, but an unknown volume of data was transmitted.

  31. Two Teams • Able to distinguish teams based on the tools and techniques used. • Forensic Profile • Able to distinguish individuals based on “keyboard behavior” – tools, techniques, command combinations, elapsed time between keyboard entries, etc. • Breach Team • Figure out how to get into the network and secure machines. • Collection Team • Determine what information to extract and implement the extraction.

  32. Data Compromised • Information extracted was very carefully selected. • Files picked out of directories of related information • Files generally were not opened pripr to extraction • Suggests that intruders had very detailed knowledge of the information in the network and had been able to search through the files to identify what they wanted. • Took a lot of time • Took detailed knowledge of the company

  33. Activity prior to exfiltration • Information Security (IS) detected low levels of intrusive activity prior to exfiltration. • Seemed to be focused on maintenance of their presence within the network • When detected IS would block the link. • Apparently intruders were able to open up other links undetected to continue their reconaissance. • Process continued for several days (at least).

  34. Reconnaissance Phase • Identify specific files, directories and file shares that contained desirable information • Identify specific users who would have access to desired information and compromise their accounts. • Uncover and use password policies • Identify group memberships • Construct detailed network architecture diagrams to facilitate information movement • Process was very methodical and quiet.

  35. Data Exfiltration Operation External Command and Control (C2) Cmd / Control Compromised users Work station Work station Staging Sys via RDP Staging Staging Staging Staging File Server File Server File Server Sending Hosts (Internal) Exfilt Host Exfilt Host Exfilt Host Collection Host (External) External Host External Host External Host

  36. Analysis • Used dozens of accounts over about 150 occasions to gather information. • Very difficult to correlate the activities prior to exfiltration. • Group memberships were particularly important in accessing data from non-compromised accounts.

  37. Data Staging Process • Took place over several days • Noticed an increase in short duration communications • Appeared to be used to verify resources, set up redundant channels, etc. • Transfer done in the evening (same time each night). • Transfer desired data from file servers to mail servers. • 75% of the company’s several dozen mail servers were involved in the intrusion. • Rename files to resemble legitimate Windows files on mail servers. • Encrypt and compress files into 650 MB RAR archives

  38. Exfiltration • Secure a compromised user machine for use as an internal C2 station • Move data into staging servers • Test all staging servers by downloading a 20MB video file. • Terminated download before complete. • Identify local (US) external hosts to receive the data • Used several versions of FTP (both standard and customized versions) to get a working configuration for offloading files. • Finally got a working configuration to a US University site. • Replicated the configuration 5 more times to increase throughput. • Eventually detected and blocked. IS noted repeated attempts over the next 5 hours to regain access.

  39. References • Stealth Coordinated Attack HOWTOby Dragos Ruiu – 1999 • Google for a copy (it seems to move around)‏ • Network Intrusion Detection 3rd ed.- Northcutt and Novak – New Riders Publishing 2003 • Maximum Linux Security – Anonymous – Sams Publishing – 2000 • Ethical Hacking and Network Defense – Simpson – Thomson Course Technonogy – 2006 • Smashing the Stack for Fun and Profit • • PRC and Cyber Warfare •

  40. Summary • There are many ways that hackers can get into systems • Complexity of systems today makes it difficult to protect all possible attack vectors. • Several web sites available to identify trends (SANS, etc.)‏ • Understand the process!