EDR Is Coming; Hide Yo Sh!t

There’s a new, largely unaddressed threat in the security industry today, Endpoint Detection and Response (EDR), which aims to stop threat actors in their tracks. The scenario plays out like this... At first your campaign is going well and your attacker objectives are being met. Then, your lovingly crafted payloads become analyst samples, you’re evicted from the environment and you lose your persistence. You and the analyst are now having a bad time. You may feel this is just fear mongering, but we assure you, the risk is real.Fortunately, we have a few new tricks up our sleeves to keep this nightmare scenario at bay. While many would have you believe that we live in a measured and signed boot Utopia on modern systems, we will show you the seedy underbelly of this Brave New World. By abusing early boot mechanisms and UEFI platform firmware, we are able to evade common detection. By showing up early to the fight, we sucker punch EDR, leaving it in a daze unable to see our malicious activities. We put a new twist on old code injection techniques and maintain persistence in UEFI firmware, making an effective invisibility cloak. By leveraging these two techniques, you and the analyst can have a happy and relaxing evening. From that point on - the good ol’ days are back again! Plunder away!

Transcript

1. EDR Is Coming; Hide yo Sh!t @TTimzen @r00tkillah
2. Who are we? Michael “@r00tkillah” Leibowitz Topher Timzen (@TTimzen) NSA Playset C# Malware is <3 Principle Troublemaker Principal Vulnerability Enthusiast RED TEAM ! ! ! !
3. Agenda • What is EDR and why do we care? • UEFI security and variables overview • Windows platform hijinks with demo • Linux platform hijinks with demo • What does this all mean? • Mitigations and Recommendations • Future work • Conclusions
4. EDR
5. Endpoint Detection and Response (EDR) Defensive tooling that focuses on detecting, investigating and mitigating suspicious activities on hosts and endpoints. Provides Blue Team a hunt capability Alerts mapped to MITRE ATT&CK via a SIEM or EDR directly CrowdStrike and Carbon Black are big players in this space
6. MITRE ATT&CK - https://attack.mitre.org/ Knowledge base of adversary tactics and techniques based on real-world observation - Tactics, Techniques, Procedures (TTP)
7. Endpoint Detection and Response (EDR) Tuned for processes, commands and API Calls • cmd.exe /c • powershell.exe • Registry modifications • Scheduled Tasks All of these mapped to MITRE TTPs
8. The Other Risk Curve Time -> Likelihood of Detection Initial shell popped Persistence phase starts
9. Result of EDR Analyst You
10. The Other Risk Curve (Modified) Time -> Likelihood of Detection Initial shell popped Persistence phase starts
11. UEFI
12. Unified Extensible Firmware Interface (UEFI) Trusted Platforms UEFI, PI and TCG-based firmware (Zimmer, Dasari, & Brogan, 2009, p. 16)
13. But Why UEFI Firmware Variables? Hides payload from AV, and EDR, and requires memory forensics to investigate EDR platform getting your reader binary doesn’t mean anything Tons of places to hide there! • Test0 E660597E-B94D-4209-9C80-1805B5D19B69 NV+BS+RT • Test1 E660597E-B94D-4209-9C80-1805B5D19B69 NV+BS+RT
14. UEFI Firmware Variables Authenticated • Secure boot nonsense (PK, KEK, db/dbx) • Performs a certificate check when writing variable Unauthenticated • No verification on write • Majority of variables are unauthenticated
15. UEFI Firmware Variable Attributes UEFI specification defines variable attributes can be • Non-volatile (NV) • Boot services access (BS) • Runtime access (RT) • Hardware error record (HR) • Count based authenticated write access • Time based authenticated write access (AT)
16. Windows Platform
17. UEFI On Windows “Starting with Windows 10, version 1803, Universal Windows apps can use GetFirmwareEnvironmentVariable and SetFirmwareEnvironmentVariable (and their 'ex' variants) to access UEFI firmware variables” SE_SYSTEM_ENVIRONMENT_NAME privilege Is required to Read/Write Administration account with Universal Windows App “required” https://docs.microsoft.com/en-us/windows/desktop/sysinfo/access-uefi-firmware-variables-from-a-universal-windows-app
18. Read/Write UEFI Firmware Variable API
19. dwAttributes Value Meaning VARIABLE_ATTRIBUTE_NON_VOLATILE 0x00000001 The firmware environment variable is stored in non-volatile memory (e.g. NVRAM). VARIABLE_ATTRIBUTE_BOOTSERVICE_ACCE SS 0x00000002 The firmware environment variable can be accessed during boot service. VARIABLE_ATTRIBUTE_RUNTIME_ACCESS 0x00000004 The firmware environment variable can be accessed at runtime. Note: Variables with this attribute set, must also have VARIABLE_ATTRIBUTE_BOOTSERVICE_ACCE SS set.
20. C++ [&& or ||] C# C++ is a viable option and was the initial language used, however • Too many API calls to Virtual* ◦ Requires RWX memory to be present for execution ◦ EDR and AV see these API calls ◦ C# can do everything needed with Reflection • More difficult to bypass WDAC • C# Allows for easy use of Cobalt Strike + Powerpick • Reference code available in repo for both
21. Steps for Writing UEFI variable 1. Obtain SE_SYSTEM_ENVIRONMENT_NAME with SetPriv() 2. Get address of a pinned buffer in C# (payload) 3. Write to UEFI variable with SetFirmwareEnvironmentVariableEx()
22. Steps for Writing UEFI variable 1. Obtain SE_SYSTEM_ENVIRONMENT_NAME with SetPriv()
23. Steps for Writing UEFI variable 2. Get address of a pinned buffer in C# (payload)
24. Steps for Writing UEFI variable 3. Write to UEFI variable with SetFirmwareEnvironmentVariableEx()
25. Steps for Executing UEFI variable 1. Obtain SE_SYSTEM_ENVIRONMENT_NAME with SetPriv() 2. P/Invoke with Virtual(Alloc, Protect) to obtain RWX Memory 3. Obtain UEFI variable payload with GetFirmwareEnvironmentVariableEx()
26. Steps for Reading UEFI variable 1. Obtain SE_SYSTEM_ENVIRONMENT_NAME with SetPriv()
27. Steps for Executing UEFI variable 2. P/Invoke with Virtual(Alloc, Protect) to obtain RWX Memory
28. C# and P/Invoke Virtual(Alloc, Protect) API Calls https://www.hybrid-analysis.com/sample/5aba178a512ae2c1c5afccf113c6dc0f80c 47fdeee294781483b8aa07002cf39/5c74860b028838095154dad0
29. C# and P/Invoke, No No
30. Steps for Executing UEFI variable 1. Obtain SE_SYSTEM_ENVIRONMENT_NAME with SetPriv() 2. P/Invoke RWX Memory 3. Obtain UEFI variable payload with GetFirmwareEnvironmentVariableEx()
31. Steps for Executing UEFI variable to Evade EDR and AV 1. Obtain SE_SYSTEM_ENVIRONMENT_NAME with SetPriv() 2. Reflectively obtain RWX JIT memory page to read UEFI variable into 3. Write UEFI variable payload to method ptr with GetFirmwareEnvironmentVariableEx() 4. Execute method
32. C# with Reflection for Method Ptr Overwrite to Execute https://www.tophertimzen.com/blog/dotNetMachineCodeManipulation/ Method Table contains address of JIT stub for a class’s methods. During JIT the Method Table is referenced Grab Method Ptr as RWX memory location and overwrite it!
33. C# with Reflection for Method Ptr Overwrite to Execute https://www.tophertimzen.com/blog/dotNetMachineCodeManipulation/ 2. Reflectively obtain RWX JIT memory page to read UEFI variable into A. Define a method to overwrite B. JIT the method C. Obtain ptr to method
34. C# with Reflection for Method Ptr Overwrite to Execute https://www.tophertimzen.com/blog/dotNetMachineCodeManipulation/ A. Define a method to overwrite
35. C# with Reflection for Method Ptr Overwrite to Execute https://www.tophertimzen.com/blog/dotNetMachineCodeManipulation/ B. JIT the method C. Obtain ptr to method
36. C# with Reflection for Method Ptr Overwrite to Execute https://www.tophertimzen.com/blog/dotNetMachineCodeManipulation/ 3. Write UEFI variable payload to method ptr with GetFirmwareEnvironmentVariableEx() 4. Execute method
37. Steps for Infection (Demo) 1. Obtain shell on target 2. Run WriteUEFICSharp 3. Set persistence for ReadUEFICSharp 4. Run ReadUEFICSharp
38. Windows Demo
39. Persistence? Exercise up to the reader WDAC Bypasses are a good means to persist with unsigned code Your payload is in a UEFI variable, GLHF Analyst!
40. What About Windows EDR Products? We saw no relevant information in EDR pertaining to the usage of UEFI variables Startup events are seen without rootkit, but no malicious activity reported • AV is clean • No Virtual* API Calls
41. Sinkhole your EDR https://gist.github.com/tophertimzen/235fbfdf6b2e3cdf255dccb763fdd805
42. WDAC Bypasses There has been a lot of research on bypassing WDAC and Windows Universal Apps - https://posts.specterops.io/arbitrary-unsigned-code-execution-v ector-in-microsoft-workflow-compiler-exe-3d9294bc5efb - https://bohops.com/2019/01/10/com-xsl-transformation-bypassi ng-microsoft-application-control-solutions-cve-2018-8492/ Singed Code is not a proper mitigation currently in Windows 10
43. Linux Platform
44. The Problem Space The Kernel Your Sample EDR
45. Envisioning The Solution The Kernel Your Payload EDR
46. Linux Boot Flow UEFI Signed by OEM
47. Linux Boot Flow UEFI shim Signed by MSFT Signed by OEM
48. Linux Boot Flow UEFI shim grub Signed by distro Signed by MSFT Signed by OEM
49. Linux Boot Flow UEFI shim grub linux Signed by distro Signed by MSFT Signed by OEM
50. Linux Boot Flow UEFI shim grub linux Signed by distro Signed by MSFT Signed by OEM Unsigned and generated on system ramdisk
51. Linux Boot Flow UEFI shim grub linux Signed by distro Signed by MSFT Signed by OEM Unsigned and generated on system ramdisk EDR
52. ptrace, Man! man (2) ptrace + PTRACE_SETREGS + PTRACE_PEEKTEXT, PTRACE_PEEKDATA + PTRACE_POKETEXT, PTRACE_POKEDATA - YAMA - SELinux/AppArmor/SMACK/TOMOYO/etc + Policy applied in userspace!!
53. Boot Flow, Continued 1 Ramdisk land
54. Boot Flow, Continued 1 1 exec Ramdisk land Rootfs land
55. Boot Flow, Continued 1 1 exec Ramdisk land Rootfs land EDR Policy load
56. fanotify, man! man (7) fanotify DESCRIPTION The fanotify API provides notification and interception of filesystem events. Use cases include virus scanning and hierarchical storage management.
57. memfd_create, man! man (2) memfd_create DESCRIPTION memfd_create() creates an anonymous file and returns a file descriptor that refers to it. The file behaves like a regular file … … it lives in RAM and has a volatile backing storage.
58. PR_SET_TIMERSLACK Since Linux 4.6, the "current" timer slack value of any process can be examined and changed via the file /proc/[pid]/timerslack_ns. See proc(5).
59. CONFIG_EFI_VARS config EFI_VARS If you say Y here, you are able to get EFI (Extensible Firmware Interface) variable information via sysfs. You may read, write, create, and destroy EFI variables through this interface.
60. Surviving MS_MOVE 1. Poll on /proc/self/mounts 2. Sleep while initramfs finishes and init starts 3. Create a new mount namespace 4. Mount proc (it's not in initramfs) 5. Set mount namespace to init's namespace through setns 6. chroot(“/proc/1/root”) 7. chdir(“.”) 8. chroot(“/”)
61. Boot Flow, Modified 1 exec Ramdisk land fork UEFI
62. Boot Flow, Modified 1 exec Ramdisk land fork UEFI open
63. Boot Flow, Modified 1 1 exec Ramdisk land Rootfs land fork UEFI
64. Boot Flow, Modified 1 1 exec Ramdisk land Rootfs land fork UEFI
65. Boot Flow, Modified 1 1 exec Ramdisk land Rootfs land fork STOP UEFI
66. Boot Flow, Modified 1 1 exec Ramdisk land Rootfs land fork ptrace UEFI
67. Ptrace 0x7fa413d56ba2 <epoll_wait+66>: mov %r13d,%r10d 0x7fa413d56ba5 <epoll_wait+69>: mov %eax,%r8d 0x7fa413d56ba8 <epoll_wait+72>: mov %r12d,%edx 0x7fa413d56bab <epoll_wait+75>: mov %rbp,%rsi 0x7fa413d56bae <epoll_wait+78>: mov %ebx,%edi 0x7fa413d56bb0 <epoll_wait+80>: mov $0xe8,%eax 0x7fa413d56bb5 <epoll_wait+85>: syscall => 0x7fa413d56bb7 <epoll_wait+87>: cmp $0xfffffffffffff000,%rax 0x7fa413d56bbd <epoll_wait+93>: ja 0x7fa413d56bf2
68. Ptrace 0x7fa413d56ba2 <epoll_wait+66>: mov %r13d,%r10d 0x7fa413d56ba5 <epoll_wait+69>: mov %eax,%r8d 0x7fa413d56ba8 <epoll_wait+72>: mov %r12d,%edx 0x7fa413d56bab <epoll_wait+75>: mov %rbp,%rsi 0x7fa413d56bae <epoll_wait+78>: mov %ebx,%edi 0x7fa413d56bb0 <epoll_wait+80>: mov $0xe8,%eax => 0x7fa413d56bb5 <epoll_wait+85>: syscall 0x7fa413d56bb7 <epoll_wait+87>: cmp $0xfffffffffffff000,%rax 0x7fa413d56bbd <epoll_wait+93>: ja 0x7fa413d56bf2 eax: 0x13f (memfd_create)
69. Ptrace 0x7fa413d56ba2 <epoll_wait+66>: mov %r13d,%r10d 0x7fa413d56ba5 <epoll_wait+69>: mov %eax,%r8d 0x7fa413d56ba8 <epoll_wait+72>: mov %r12d,%edx 0x7fa413d56bab <epoll_wait+75>: mov %rbp,%rsi 0x7fa413d56bae <epoll_wait+78>: mov %ebx,%edi 0x7fa413d56bb0 <epoll_wait+80>: mov $0xe8,%eax => 0x7fa413d56bb5 <epoll_wait+85>: syscall 0x7fa413d56bb7 <epoll_wait+87>: cmp $0xfffffffffffff000,%rax 0x7fa413d56bbd <epoll_wait+93>: ja 0x7fa413d56bf2 eax: 0x13f (memfd_create) .ELF............
70. Ptrace 0x7fa413d56ba2 <epoll_wait+66>: mov %r13d,%r10d 0x7fa413d56ba5 <epoll_wait+69>: mov %eax,%r8d 0x7fa413d56ba8 <epoll_wait+72>: mov %r12d,%edx 0x7fa413d56bab <epoll_wait+75>: mov %rbp,%rsi 0x7fa413d56bae <epoll_wait+78>: mov %ebx,%edi 0x7fa413d56bb0 <epoll_wait+80>: mov $0xe8,%eax => 0x7fa413d56bb5 <epoll_wait+85>: syscall 0x7fa413d56bb7 <epoll_wait+87>: cmp $0xfffffffffffff000,%rax 0x7fa413d56bbd <epoll_wait+93>: ja 0x7fa413d56bf2 eax: 0x9 (mmap) 0x90 0x90 0x90 0x90 0x90 .ELF............
71. Ptrace 0x7fa413d56ba2 <epoll_wait+66>: mov %r13d,%r10d 0x7fa413d56ba5 <epoll_wait+69>: mov %eax,%r8d 0x7fa413d56ba8 <epoll_wait+72>: mov %r12d,%edx 0x7fa413d56bab <epoll_wait+75>: mov %rbp,%rsi 0x7fa413d56bae <epoll_wait+78>: mov %ebx,%edi 0x7fa413d56bb0 <epoll_wait+80>: mov $0xe8,%eax 0x7fa413d56bb5 <epoll_wait+85>: syscall 0x7fa413d56bb7 <epoll_wait+87>: cmp $0xfffffffffffff000,%rax 0x7fa413d56bbd <epoll_wait+93>: ja 0x7fa413d56bf2 eax: 0x9 (mmap) => 0x90 0x90 0x90 0x90 0x90 .ELF............ ret2libc (dlopen)
72. Ptrace 0x7fa413d56ba2 <epoll_wait+66>: mov %r13d,%r10d 0x7fa413d56ba5 <epoll_wait+69>: mov %eax,%r8d 0x7fa413d56ba8 <epoll_wait+72>: mov %r12d,%edx 0x7fa413d56bab <epoll_wait+75>: mov %rbp,%rsi 0x7fa413d56bae <epoll_wait+78>: mov %ebx,%edi 0x7fa413d56bb0 <epoll_wait+80>: mov $0xe8,%eax 0x7fa413d56bb5 <epoll_wait+85>: syscall => 0x7fa413d56bb7 <epoll_wait+87>: cmp $0xfffffffffffff000,%rax 0x7fa413d56bbd <epoll_wait+93>: ja 0x7fa413d56bf2 eax: 0x9 (mmap) 0x90 0x90 0x90 0x90 0x90 .ELF............ ret
73. Boot Flow, Modified 1 1 exec Ramdisk land Rootfs land fork CONT UEFI
74. Boot Flow, Modified 1 1 exec Ramdisk land Rootfs land fork UEFI
75. Linux Demo 1. See noise in auditd of exploiting enterprise_tool 2. Install implant into UEFI and ramdisk 3. Reboot 4. Set timerslack marker 5. Exploit enterprise_tool 6. See no output in log 7. Show policy in place 8. Show variable
76. Linux Demo
77. What does this all mean?
78. Net Happiness Increase You Analyst
79. Mitigations and Recommendations
80. Mitigations and Recommendations Monitor and Audit UEFI variables across your organizations fleet EDR Should detect UEFI APIs • It is not common for apps to Set/Get Firmware Variables • NV+BS+RT Variables are suspicious if created after installation of platform
81. Mitigations and Recommendations EDR Tamper Resistance is not effective • Sinkholing or killing the sensor usually does not give alerts • Vendors need to work on securing their processes ◦ Alert on sinkhole ◦ Do not allow ptrace Stop assembling ramdisks on systems!
82. Closing and the Rest
83. Future Work Look into hiding inside of UEFI Configuration Storage Analyze more EDR products and how they handle UEFI variables Use these techniques in more Red Team engagements to increase defender efficacy Look at more platforms for their usage of UEFI variables • More places to hide
84. Closing Have yourself a uefi.party and plunder away your loot! Sucker punch that pesky EDR! GitHub Repo at https://github.com/perturbed-platypus
85. References https://redcanary.com/blog/detecting-all-the-things-with-limited-data/ https://countercept.com/blog/av-bypass-techniques-through-an-edr-lens/ https://github.com/rrbranco/BlackHat2017/blob/master/BlackHat2017-BlackBIOS-v0.13-Published.pdf https://github.com/emptymonkey/ptrace_do https://github.com/eklitzke/ptrace-call-userspace https://magisterquis.github.io/2018/03/31/in-memory-only-elf-execution.html
86. References for MITRE TTPs Tuned for processes, commands and API Calls • cmd.exe /c ◦ https://attack.mitre.org/techniques/T1059/ • powershell.exe ◦ https://attack.mitre.org/techniques/T1086/ • Registry modifications ◦ https://attack.mitre.org/techniques/T1112/ • Scheduled Tasks ◦ https://attack.mitre.org/techniques/T1053/
87. EOF