1. A Study on NetSpectre
@ 若渴 2019.4.14
<ajblane0612@gmail.com>
AjMaChInE

2. No code can be injected and Attacker
only calls the API via network requests
-> ?
-> leak information (ASLR/ Password)
NetSpectre

3. Key idea
在程式碼中，找到某些程式碼 (gadget) ，這個
gadget 搭配手法 (attacker-controlled) 會使得
microarchitecture elements 有些 side effect ，而這 side
effect 可以透過一些測量 (measurement) 來觀察，
透過 side effect 與 gadget 搭配可以達到某些目的
(E.g. 推敲出一些重要的訊息 ) 。
● cache-side channel attack
● spectre variant 1
● ...

4. Cache-side channel attack
– how to retrieve information [0]
e.g. E= (1,…,0,0)
I cache
attacker victim

5. Cache-side channel attack
– how to retrieve information [0]

6. Cache-side channel attack
– how to retrieve information [0]
Access

7. ● Gadget
● Montgomery ladder RSA
● Attacker-controlled
● Flush and reload
● Microarchitecture element
● I Cache
● Measure access time
● Purpose
● Secret E

8. Speculate execution [1]

9. Speculate execution [1]

10. Speculate execution [1]

11. Speculate execution [1]

12. Assumptions [1]
共用
cache into not
same entry
cache into not
same entry
can reset cache

13. Spectre-PHT (aka Spectre Variant 1) [1]
Step 1: reset cache

14. Spectre-PHT (aka Spectre Variant 1) [1]
Step 2: out-of-bounds
read

15. Spectre-PHT (aka Spectre Variant 1) [1]
* glyph[X] – X is attacker-controlled
* cache-side channel attack
→ cache hit → X=K
→ cache miss → X!=K
Step 3: cache-side
channel attack

16. Repeatly run step 1 ~ 3 -> leak memory via
byte by byte

17. ● Gadget
●
● Attacker-controlled
● If (x < array1_size)
● array2[X * 4096], array2 is shared memory
● Chache-side channel attack
● Microarchitecture element
● D Cache
● Purpose
● Memory content of out-of-bounds array

18. NetSpectre - the big picture

19. ● Gadget
● Leak gadget
● Attacker-controlled
● Network API -> x
● Microarchitecture element
● Transmit gadget
● Network latency depends on API execution time (transmit
gadget)
→ Measure the network roundtrip time
● Information
● Memory content of out-of-bounds array

20. Measuring the response time of a simple transmit gadget,
that accesses a certain variable. Only by performing a large
number of measurements, the difference in the response
timings depending on the cache state of the variable
becomes visible. The average values of the two distributions
are shown as dashed vertical lines [2]

21. Leaking a byte via bit by bit
[2][3]

22. Problem - how to find a gadget [2]
● Finding Spectre gadgets is still an open problem
● Out of all papers, only 4 show real-world gadgets [3]
● Among them, only 2 Spectre-PHT (v1) gadgets
● Still no fully automated approach
● Tainted flow analysis

23. ● Gadget
● ??
● Attacker-controlled
● ??
● Microarchitecture element
● ??
● Measure ??
● Purpose
● ??

24. NetSpectre
ALSR
Network API (x)

26. Remote AVX-based covert channel against
cache [2]

27. Reference
● [0] 2017, Cache Side Channel Attack: Exploitability and
Countermeasures
● [1] 2019, NetSpectre A Truly Remote Spectre Variant
● [2] 2018, NetSpectre: Read Arbitrary Memory over
Network
● [3] 2018, Spectre Attacks: Exploiting Speculative
Execution