ROP is Still Dangerous: Breaking Modern Defenses

Nicholas Carlini et. alUniversity of California, Berkeley

USENIX Security 2014Presenter: Yue Li

Part of the slides from N. Carlini

Outline

BackgroundROP AttacksAttack PrimitivesAttack Goal and Threat ModelkBouncerROPeckerEvaluationRelated Work and Conclusion

Background

Code injection ● Usually exploited in a buffer overrun vulnerability.

● Inject malicious code● Overwrites return address of

a function.● Return address -> malicious

code

Background

Code injection Data Execution Prevention (DEP) ● Security feature in modern

OS● Ensures writable pages in

memory are not executable● Stack is no longer

executable● Code cannot be injected

Background

Code injection Data Execution Prevention (DEP)

Return Oriented Programming (ROP)

Outline

BackgroundROP AttacksAttack PrimitivesAttack Goal and Threat ModelkBouncerROPeckerEvaluationRelated Work and Conclusion

ROP Attacks

Gadgets !

ROP Attacks

● Perform malicious computation by only controlling the execution flow

● Each gadget performs small computation● Gadget chaining is achieved by influencing

indirect jumps● Need to write appropriate values over the

stack

ROP Attacks

1. eax stores 4a3041202. ebs stores 000324003. eax stores [4a304120] (OV)4. eax stores (OV + 00032400)5. ecx stores 4a3041206. [4a304120] stores (OV +

00032400)

ROP AttacksDefend ROP

Outline

BackgroundROP AttacksAttack PrimitivesAttack Goal and Threat ModelkBouncerROPeckerEvaluationRelated Work and Conclusion

Attack Primitives

Three building blocks are useful in attacking ROP defenses

1. Call-Preceded ROP2. Evasion Attack3. History Flushing

Call-Preceded ROPCall-Preceded Policy: Normally, every ret will return to an instruction that immediately follows a call

Call-Preceded ROP● The call-preceded policy limit the

choices of gadgets● Only 6% of gadgets are call-

preceded● People believe the call-preceded

policy significantly increases the difficulty of mounting a ROP.

● However, the authors argue it is possible to mount ROP with this policy

● Allow more complex gadgets.● 70KB of binary code

Evasion Attacks

Classification-based defense● Monitoring the runtime behavior of a process● Classify segments of execution as either “gadget” or

“non-gadget”● Length-based classifier (instructions separated by

indirect instructions● Long sequences of short gadgets -> ROP attack

Evasion Attacks

To break classification-based defense

● Using gadgets that look like benign execution● An evasion attack is one that will be classified by the

defense as normal. ● Actually evasion attack allows the attacker to mount a

ROP

History flushing

History inspection defense

● Inspect program at different points throughout its execution

● Limited amount of history● due to performance consideration, usually the

inspection is invoked in certain points (issue a system call)

History flushing

To break History inspection defense

● Fool the defense by hiding ROP attack● Perform ROP when not being watched● Insert effective no-op instructions, stop making progress

when being watched

Outline

BackgroundROP AttacksAttack PrimitivesAttack Goal and Threat ModelkBouncerROPeckerEvaluationRelated Work and Conclusion

Attack Goal and Threat Model

Attack Goal:● Issue a single syscall● mprotect (Linux) or virtualprotect (windows), making a

page in memory both executable and writable

Threat Model:● Attacker has a known exploit to control the instruction

pointer in the future● Typically it is a stack overflow

Outline

BackgroundROP AttacksAttack PrimitivesAttack Goal and Threat ModelkBouncerROPeckerEvaluationRelated Work and Conclusion

kBouncer

kBouncer: a scheme that uses indirect branch tracing to detect ROP attacks● Uses the Last Branch Record (LBR) to inspect the last 16 indirect

branches each● Run when a system call is invoked● Low overhead● Check 2 properties

o Call-preceded?o Are 8 most recent gadget-like? (<20 instructions before an indirect

branch)

kBouncerDetected !

kBouncer

History Hiding Attack● Uses history flushing to clear evidence of ROP● 3 steps

o Initial exploitation: normal ROP attack (may not be call-preceded) until a syscall is about to be invoked

o Hide the history: flush the historyo Restore registers and issue the system call

kBouncer

Flush the history● Consists of a short flushing gadget

and a long termination gadget

● Short flushing gadget - satisfy call-proceded requirement

● Repeat short flushing gadget 16 times

● Termination gadget - at least 20 instructions (non-gadget)

kBouncer - Flush History

kBouncer

Restore registers ● Can be achieved with a few gadgets that pop register

values off the stack● Other ways

o Jump Oriented Programming (JOP)o Call Oriented Programming (COP)o etc

kBouncer

What happens if kBouncer keeps the whole execution history? - can still be broken

● Initial phase will use only call-preceded gadget● No flushing gadget is needed● Break up short gadget chains with long termination gadget● 70KB of program will have enough call-preceded calls to finish such a ROP

attack

Outline

BackgroundROP AttacksAttack PrimitivesAttack Goal and Threat ModelkBouncerROPeckerEvaluationRelated Work and Conclusion

ROPecker

ROPecker is a defense that builds on ideas found in kBouncerWith a few differences● Inspect more frequently● Only a few pages are marked executable at one time● Will be invoked each time a page not in executable set is executed● Syscalls● It looks both history and future to detect attack● Future emulation will stop when there is not a short sequence of instruction

leading to an indirect jumpROPecker: A generic and practical approach for defending against rop attacks. Yueqiang Cheng, Zongwei Zhou, Miao Yu, Xuhua Ding, and Robert H Deng. NDSS, 2014.

ROPecker

Repeated History Hiding Attack● repeatedly invokes the history hiding primitives● 3 phases

o Loading phase: load useful pages into executable seto Attack phase: invokes gadgets on these pageso Flushing phase: mounts the history hiding attack using only gadgets

from these pages

● May need to execute the 3 phases multiple time to achieve the goal

ROPecker

ROPecker

Attack ROPecker is more complicated

● Carefully pick tasks during each step● Flushing and Termination gadgets clober register states● Pick independent operations for each step● Pick pages that contain more gadgets

ROPecker

Evasion Attack

● Let ROPecker inspect at any time● Insert a termination gadget in between every ten useful

gadgets.● Threshold is 11 (past and future)

Outline

BackgroundROP AttacksAttack PrimitivesAttack Goal and Threat ModelkBouncerROPeckerEvaluationRelated Work and Conclusion

Evaluation● A tool is built to find attacks on real-world exploits● The tool help find gadgets● Enumerate all potential call-preceded gadgets

Evaluation

Modify Real-world Exploits to bypass kBouncer● 4 real-world exploits are modified

o MPlayer Lite r33063 Stack-based buffer overflow, exploited by overwriting SEH pointer

o Adobe Reader 9.3.4o Adobe Flash 11.3.300o Internet Explorer 8

● Half a day to cloak the attacks

Evaluation

Use exploitable version of hteditor source to bypass ROPecker

● Evasion attack● Repeated history hiding attack● execv is issued eventually

Outline

BackgroundROP AttacksAttack PrimitivesAttack Goal and Threat ModelkBouncerROPeckerEvaluationRelated Work and Conclusion

Related Work

● [Goktas, S&P14] discussed the existence of call-preceded ROP and use it to break many existing CFI defenses

● [Davi, Usenix14] and [Goktas, Usenix14] both independently and concurrently discovered

very similar attacks on kBouncer & ROPecker

Conclusion

This paper has presented:● 3 building blocks for ROP attacks● Break state-of-art defenses - kBouncer and ROPecker● Implication

o Do not rely on limited historyo Call-preceded ROP is possibleo Difficult to classify “gadget” and “non-gadget”o Focus on fundamental difference between normal

and ROP execution