CAPEC-663: Exploitation of Transient Instruction Execution
Attack Pattern ID: 663
Abstraction: Standard
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Description
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.
Likelihood Of Attack
Low
Typical Severity
Very High
Relationships
This table shows the other attack patterns and high level categories that are related to this attack pattern. These relationships are defined as ChildOf and ParentOf, and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as CanFollow, PeerOf, and CanAlsoBe are defined to show similar attack patterns that the user may want to explore.
Nature
Type
ID
Name
ChildOf
Meta Attack Pattern - A meta level attack pattern in CAPEC is a decidedly abstract characterization of a specific methodology or technique used in an attack. A meta attack pattern is often void of a specific technology or implementation and is meant to provide an understanding of a high level approach. A meta level attack pattern is a generalization of related group of standard level attack patterns. Meta level attack patterns are particularly useful for architecture and design level threat modeling exercises.
Meta Attack Pattern - A meta level attack pattern in CAPEC is a decidedly abstract characterization of a specific methodology or technique used in an attack. A meta attack pattern is often void of a specific technology or implementation and is meant to provide an understanding of a high level approach. A meta level attack pattern is a generalization of related group of standard level attack patterns. Meta level attack patterns are particularly useful for architecture and design level threat modeling exercises.
Detailed Attack Pattern - A detailed level attack pattern in CAPEC provides a low level of detail, typically leveraging a specific technique and targeting a specific technology, and expresses a complete execution flow. Detailed attack patterns are more specific than meta attack patterns and standard attack patterns and often require a specific protection mechanism to mitigate actual attacks. A detailed level attack pattern often will leverage a number of different standard level attack patterns chained together to accomplish a goal.
Meta Attack Pattern - A meta level attack pattern in CAPEC is a decidedly abstract characterization of a specific methodology or technique used in an attack. A meta attack pattern is often void of a specific technology or implementation and is meant to provide an understanding of a high level approach. A meta level attack pattern is a generalization of related group of standard level attack patterns. Meta level attack patterns are particularly useful for architecture and design level threat modeling exercises.
Standard Attack Pattern - A standard level attack pattern in CAPEC is focused on a specific methodology or technique used in an attack. It is often seen as a singular piece of a fully executed attack. A standard attack pattern is meant to provide sufficient details to understand the specific technique and how it attempts to accomplish a desired goal. A standard level attack pattern is a specific type of a more abstract meta level attack pattern.
Meta Attack Pattern - A meta level attack pattern in CAPEC is a decidedly abstract characterization of a specific methodology or technique used in an attack. A meta attack pattern is often void of a specific technology or implementation and is meant to provide an understanding of a high level approach. A meta level attack pattern is a generalization of related group of standard level attack patterns. Meta level attack patterns are particularly useful for architecture and design level threat modeling exercises.
Standard Attack Pattern - A standard level attack pattern in CAPEC is focused on a specific methodology or technique used in an attack. It is often seen as a singular piece of a fully executed attack. A standard attack pattern is meant to provide sufficient details to understand the specific technique and how it attempts to accomplish a desired goal. A standard level attack pattern is a specific type of a more abstract meta level attack pattern.
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.
Techniques
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.
Techniques
Run OS or application specific tools that examine the contents of cache.
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.
Techniques
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.
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.
Techniques
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.
Prerequisites
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.
Skills Required
[Level: High]
Detailed knowledge on how various CPU architectures and microcode perform transient execution for various low-level assembly language code instructions/operations.
[Level: 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.
Resources Required
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.
Indicators
File Signatures for Malicious Software capable of abusing Transient Instruction Set Execution
Consequences
This table specifies different individual consequences associated with the attack pattern. The Scope identifies the security property that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in their attack. The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. For example, there may be high likelihood that a pattern will be used to achieve a certain impact, but a low likelihood that it will be exploited to achieve a different impact.
Scope
Impact
Likelihood
Confidentiality
Read Data
Access Control
Bypass Protection Mechanism
Authorization
Execute Unauthorized Commands
Mitigations
Implementation: DAWG (Dynamically Allocated Way Guard) - processor cache properly divided between different programs/processes that don't share resources
Implementation: KPTI (Kernel Page-Table Isolation) to completely separate user-space and kernel space page tables
Configuration: Architectural Design of Microcode to limit abuse of speculative execution and out-of-order execution
Configuration: Disable SharedArrayBuffer for Web Browsers
Configuration: Disable Copy-on-Write between Cloud VMs
Configuration: Privilege Checks on Cache Flush Instructions
Implementation: Non-inclusive Cache Memories to prevent Flush+Reload Attacks
Example Instances
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.
Related Weaknesses
A Related Weakness relationship associates a weakness with this attack pattern. Each association implies a weakness that must exist for a given attack to be successful. If multiple weaknesses are associated with the attack pattern, then any of the weaknesses (but not necessarily all) may be present for the attack to be successful. Each related weakness is identified by a CWE identifier.
Hardware Logic with Insecure De-Synchronization between Control and Data Channels
References
[REF-637] Paul Kocher, Jann Horn, Anders Fogh, Daniel Genkin, Daniel Gruss, Werner Haas, Mike Hamburg, Moritz Lipp, Stefan Mangard, Thomas Prescher, Michael Schwarz
and Yuval Yarom. "Spectre Attacks: Exploiting Speculative Execution". Graz University of Technology. 2019.
<https://spectreattack.com/spectre.pdf>. URL validated: 2021-03-05.
[REF-638] Moritz Lipp, Michael Schwarz, Daniel Gruss, Thomas Prescher, Werner Haas, Anders Fogh, Jann Horn, Stefan Mangard, Paul Kocher, Daniel Genkin, Yuval Yarom
and Mike Hamburg. "Meltdown: Reading Kernel Memory from User Space". Graz University of Technology. 2018.
<https://meltdownattack.com/meltdown.pdf>. URL validated: 2021-03-05.
[REF-639] Claudio Canella, Jo Van Bulck, Michael Schwarz, Moritz Lipp, Benjamin von Berg, Philipp Ortner, Frank Piessens, Dmitry Evtyushkin
and Daniel Gruss. "A Systematic Evaluation of Transient Execution Attacks and Defenses". Graz University of Technology. 2019-05-15.
<https://arxiv.org/abs/1811.05441>. URL validated: 2021-03-05.
[REF-640] Qian Ge, Yuval Yarom
and Gernot Heiser. "A Survey of Microarchitectural Timing Attacks and Countermeasures on Contemporary Hardware". Journal of Cryptographic Engineering. 2016-12-26.
<https://eprint.iacr.org/2016/613.pdf>. URL validated: 2021-03-05.
Description
This table shows the other attack patterns and high level categories that are related to this attack pattern. These relationships are defined as ChildOf and ParentOf, and give insight to similar items that may exist at higher and lower levels of abstraction. In addition, relationships such as CanFollow, PeerOf, and CanAlsoBe are defined to show similar attack patterns that the user may want to explore.
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