Obfuscated malware detection
View Patent ↗Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for obfuscated malware. In one aspect, a method includes executing from a binary executable a call instruction and a plurality of instruction subsequent to a target of the call instruction, determining if the value identified by the stack pointer of the call stack is equal to a default value stored in the call stack prior to emulation, determining if there is a non-obfuscation signal resulting from the execution of the call instructions and the plurality of instructions, and if the value identified by the stack pointer is the default value and there is no obfuscation signal, identifying the call instruction as a possibly obfuscated call instruction; Additionally, the method includes determining that if the number of call instructions identified as possibly obfuscated call instructions exceeds a threshold number, identifying the binary executable as an obfuscated executable.
1. A computer-implemented method, comprising:
identifying a number of call instructions in a binary executable;
for each of the number of call instructions:
storing in a call stack a default value generated for the call instruction;
executing the call instruction, wherein executing the call instruction causes a return address after the call instruction to be stored in the call stack;
sequentially executing a plurality of instructions subsequent to a target of the call instruction;
determining that a value identified by a stack pointer of the call stack is equal to the default value;
in response to the determination that the value identified by the stack pointer is equal to the default value, determining if there is a non-obfuscation signal present;
if there is a non-obfuscation signal present, identifying the call instruction as a non-obfuscated call instruction;
if there is not a non-obfuscation signal present, identifying the call instruction as a possibly obfuscated call instruction;
determining whether the call instructions identified as possibly obfuscated call instructions exceeds a threshold number;
in response to the determination that the call instructions identified as possibly obfuscated call instructions exceeds the threshold number, identifying the binary executable as an obfuscated executable; and
in response to the determination that the call instructions identified as possibly obfuscated call instructions do not exceed the threshold number, identifying the binary executable as a non-obfuscated executable.
2. The method of claim 1 , wherein identifying a number of call instructions in a binary executable comprises identifying call instructions in the binary executable, wherein for each of the identified call instructions a target of the call instruction has an offset that is unique from offsets of targets of any of the other identified call instructions, and wherein the offset of a target of the call instruction is a position of the target of the call in the binary executable relative to a memory space addressed at a beginning address of the binary executable.
3. The method of claim 1 , wherein determining if there is a non-obfuscation signal present comprises:
determining whether the call instruction executed; and
if the call instruction did not execute, then identifying the call instruction as a non-obfuscated call instruction.
4. The method of claim 1 , wherein determining if there is a non-obfuscation signal present comprises:
determining whether an instruction pointer points to the call instruction; and
if the instruction pointer points to the call instruction, then identifying the call instruction as a non-obfuscated call instruction.
5. The method of claim 4 , further comprising:
if the instruction pointer does not point to the call instruction, determining whether the instruction pointer points to a next instruction after the call instruction;
if the instruction pointer points to the next instruction after the call instruction, identifying the call instruction as a non-obfuscated call instruction; and
if the instruction pointer does not point to the next instruction after the call instruction, identifying the call instruction as a possibly obfuscated call instruction.
6. The method of claim 1 , wherein determining if there is a non-obfuscation signal present comprises:
determining whether an instruction pointer points to a next instruction after the call instruction;
if the instruction pointer points to the next instruction after the call instruction, identifying the call instruction as a non-obfuscated call instruction; and
if the instruction pointer does not point to the next instruction after the call instruction, identifying the call instruction as a possibly obfuscated call instruction.
7. The method of claim 1 , further comprising:
identifying in the plurality of instructions subsequent to a target of the call instruction a subsequent call instruction; and
converting each subsequent call instruction to a non-operational instruction.
8. The method of claim 7 , wherein identifying a subsequent call instruction comprises identifying subsequent call instructions only within a control range of the target, the control range being a predetermined range of bytes within the target.
9. The method of claim 8 further comprising:
determining whether any of the plurality of instructions reference a location outside the control range from the target of the call instruction;
if the location is not outside the control range, processing the plurality of instructions; and
if the location is outside the control range, identifying the call instruction as a non-obfuscated call instruction.
10. A system, comprising:
one or more computers; and;
a computer-readable medium coupled to the one or more computers having instructions stored thereon which, when executed by the one or more computers, cause the one or more computers to perform operations comprising:
identifying a number of call instructions in a binary executable;
for each of the number of call instructions:
storing in a call stack a default value generated for the call instruction;
executing the call instruction, wherein executing the call instruction causes a return address after the call instruction to be stored in the call stack;
sequentially executing a plurality of instructions subsequent to a target of the call instruction;
determining that a value identified by a stack pointer of the call stack is equal to the default value;
in response to the determination that the value identified by the stack pointer is equal to the default value, determining if there is a non-obfuscation signal present;
if there is a non-obfuscation signal present, identifying the call instruction as a non-obfuscated call instruction;
if there is not a non-obfuscation signal present, identifying the call instruction as a possibly obfuscated call instruction;
determining whether the call instructions identified as possibly obfuscated call instructions exceeds a threshold number;
in response to the determination that the call instructions identified as possibly obfuscated call instructions exceeds the threshold number, identifying the binary executable as an obfuscated executable; and
in response to the determination that the call instructions identified as possibly obfuscated call instructions do not exceed the threshold number, identifying the binary executable as a non-obfuscated executable.
11. The system of claim 10 , wherein identifying a number of call instructions in a binary executable comprises identifying call instructions in the binary executable wherein for each of the identified called instructions a target of the call instruction has an offset that is unique from offsets of targets of any of the other identified call instructions, and wherein the offset of a target of the call instruction is a position of the target of the call in the binary executable relative to a memory space addressed at a beginning address of the binary executable.
12. The system of claim 10 , wherein determining if there is a non-obfuscation signal present comprises:
determining whether an instruction pointer points to the call instruction; and
if the instruction pointer points to the call instruction, then identifying the call instruction as a non-obfuscated call instruction.
13. The system of claim 12 , further comprising:
if the instruction pointer does not point to the call instruction, determining whether the instruction pointer points to a next instruction after the call instruction;
if the instruction pointer points to the next instruction after the call instruction, identifying the call instruction as a non-obfuscated call instruction; and
if the instruction pointer does not point to the next instruction after the call instruction, identifying the call instruction as a possibly obfuscated call instruction.
14. The system of claim 10 , wherein determining if there is a non-obfuscation signal present comprises:
determining whether an instruction pointer points to a next instruction after the call instruction;
if the instruction pointer points to the next instruction after the call instruction, identifying the call instruction as a non-obfuscated call instruction; and
if the instruction pointer does not point to the next instruction after the call instruction, identifying the call instruction as a possibly obfuscated call instruction.
15. The system of claim 10 , further comprising:
identifying in the plurality of instructions subsequent to a target of the call instruction a subsequent call instruction; and
converting each subsequent call instruction to a non-operational instruction.
16. The system of claim 15 , wherein identifying a subsequent call instruction comprising identifying subsequent call instructions only within a control range of the target, the control range being a predetermined range of bytes within the target.
17. The system of claim 16 further comprising:
determining whether any of the plurality of instructions reference a location outside the control range from the target of the call instruction;
if the location is not outside the control range, processing the plurality of instructions; and
if the location is outside the control range, identifying the call instruction as a non-obfuscated call instruction.