COMMON ATTACK PATTERN ENUMERATION AND CLASSIFICATIONMITRE canlı kaydı

CAPEC-663

Exploitation of Transient Instruction Execution

An adversary exploits a hardware design flaw in a CPU implementation of transient instruction execution to expose sensitive data and bypass/subvert access control over restricted resources. Typically, the adversary conducts a covert channel attack to target non-discarded microarchitectural changes caused by transient executions such as speculative execution, branch prediction, instruction pipelining, and/or out-of-order execution. The transient execution results in a series of instructions (gadgets) which construct covert channel and access/transfer the secret data.

Soyutlama

Standard

Tipik ciddiyet

Very High

Saldırı ihtimali

Low

Saldırıyı anla

Bu saldırı kalıbı nedir?

An adversary exploits a hardware design flaw in a CPU implementation of transient instruction execution to expose sensitive data and bypass/subvert access control over restricted resources. Typically, the adversary conducts a covert channel attack to target non-discarded microarchitectural changes caused by transient executions such as speculative execution, branch prediction, instruction pipelining, and/or out-of-order execution. The transient execution results in a series of instructions (gadgets) which construct covert channel and access/transfer the secret data.

Uygulama akışı

Saldırı adım adım nasıl ilerler?

1

Explore

Survey target application and relevant OS shared code libraries

Adversary identifies vulnerable transient instruction sets and the code/function calls to trigger them as well as instruction sets or code fragments (gadgets) to perform attack.

Kullanılan teknikler

  • Utilize Disassembler and Debugger tools to examine and trace instruction set execution of source code and shared code libraries on a system.

Explore cache and identify impacts

Utilize tools to understand the impact of transient instruction execution upon address spaces and CPU operations.

Kullanılan teknikler

  • Run OS or application specific tools that examine the contents of cache.
2

Experiment

Cause conditions for identified transient instruction set execution

Adversary ensures that specific code/instructions of the target process are executed by CPU, so desired transient instructions are executed.

Cause specific secret data to be cached from restricted address space

Executed instruction sets (gadgets) in target address space, initially executed via adversary-chosen transient instructions sets, establish covert channel and transfer secret data across this channel to cache.

Kullanılan teknikler

  • Prediction-based - adversary trains CPU to incorrectly predict/speculate conditions for instruction execution to be true, hence executing adversary-chosen transient instructions. These prediction-based methods include: Pattern History Table (PHT)/Input Validation Bypass, Branch Target Buffer (BTB)/Branch Target Injection, Return Stack Buffer (RSB)/Return Address Injection, and Store To Load (STL)/Speculative Store Bypass.
  • Exception/Fault-based - adversary has CPU execute transient instructions that raise an exception allowing inaccessible memory space to be accessed via out-of-order execution. These exception/fault-based methods include: Supervisor-only Bypass, Virtual Translation Bypass, System Register Bypass, FPU Register Bypass, Read-only Bypass, Protection Key Bypass, and Bounds Check Bypass.
3

Exploit

Perform covert channel attack to obtain/access secret data

Adversary process code removes instructions/data from shared cache set, waits for target process to reinsert them back into cache, to identify location of secret data via a timing method. Adversary continuously repeat this process to identify and access entirety of targeted secret data.

Kullanılan teknikler

  • Flush+Reload - adversary frequently flushes targeted memory cache line using a dedicated machine flush instruction, and uses another process to measure time taken for CPU to load victim secret data.
  • Evict+Time - adversary causes victim to load target set into cache and measures time for victim process to load this data, setting a baseline. Adversary evicts a specified cache line and causes victim process to execute again, and measures any change in execution time, to determine if cache line was accessed.
  • Prime+Probe - adversary primes cache by filling cache line(s) or set(s) with data, after some time victim process evicts this adversary data to replace it with secret data. The adversary then probes/accesses all the previously accessed cache lines detecting cache misses, which determine that their attacker data has been evicted and replaced with secret data from victim process.

Gereksinimler

Saldırının gerçekleşmesi için ne gerekir?

Ön koşullar

  • The adversary needs at least user execution access to a system and a maliciously crafted program/application/process with unprivileged code to misuse transient instruction set execution of the CPU.

Gerekli beceri

  • High: Detailed knowledge on how various CPU architectures and microcode perform transient execution for various low-level assembly language code instructions/operations.
  • High: Detailed knowledge on compiled binaries and operating system shared libraries of instruction sequences, and layout of application and OS/Kernel address spaces for data leakage.

Gerekli kaynak

  • C2C mechanism or direct access to victim system, capable of dropping malicious program and collecting covert channel attack data.
  • Malicious program capable of triggering execution of transient instructions or vulnerable instruction sequences of victim program and performing a covert channel attack to gather data from victim process memory space. Ultimately, the speed with which an attacker discovers a secret is directly proportional to the computational resources of the victim machine.

Tespit

Saldırının göstergeleri nelerdir?

File Signatures for Malicious Software capable of abusing Transient Instruction Set Execution

Etki

Başarılı saldırı neye yol açar?

Read Data

Etkilenen alanlar: Confidentiality

Bypass Protection Mechanism

Etkilenen alanlar: Access Control

Execute Unauthorized Commands

Etkilenen alanlar: Authorization

Savunma

Nasıl önlenir ve etkisi azaltılır?

1
Implementation: DAWG (Dynamically Allocated Way Guard) - processor cache properly divided between different programs/processes that don't share resources
2
Implementation: KPTI (Kernel Page-Table Isolation) to completely separate user-space and kernel space page tables
3
Configuration: Architectural Design of Microcode to limit abuse of speculative execution and out-of-order execution
4
Configuration: Disable SharedArrayBuffer for Web Browsers
5
Configuration: Disable Copy-on-Write between Cloud VMs
6
Configuration: Privilege Checks on Cache Flush Instructions
7
Implementation: Non-inclusive Cache Memories to prevent Flush+Reload Attacks

Gerçek dünya

MITRE örnek olayları

Örnek olay 1Detay
A web browser with user-privileges executes JavaScript code imbedded within a malicious website. The system does not disable shared buffers for the web browser and there is no restriction or check upon user-process execution of flush or evict instructions. The Javascript code executes vulnerable transient instructions upon system to cause microarchitectural changes that establish covert channel and transfer sensitive/secret data into shared cache from address space of either kernel, web browser or another executing process on the system.