metamorphic malware analysis and detection

Bioinformatics Techniques for Metamorphic Malware Analysis

and Detection

Malaviya National Institute of Technology, Jaipur

and Detection

Supervisors:

Dr. M. S. Gaur

Dr. V. Laxmi

Grijesh Chauhan

(2009PCP116)

Outline

� Malware & Metamorphic malware

� Motivation

� Objective

� BioinformaticsTechniques� BioinformaticsTechniques

� MOMENTUM

� Dataset

� Result & Analysis

� References

Malware

� Malware are software with intentions to infect andreplicate.

� Threats

� Lossof data

� Degrades computer system performance

� Identity threat

� Two broad categories

� Metamorphic: Virus body changes on each replication

� Polymorphic: Encrypts malicious payload to avoiddetection

Metamorphic Malware[1/2]

� Metamorphic malware have similarfunctionality, different structure and signature.

� Similar to genetic diversity in Biology.

Variant -1 Variant -2 Variant -3

Metamorphic Engine

Diagram depicts metamorphic malware variants with reordered code

Metamorphic Malware[1/2]

� Metamorphic Malware automatically re-codes itselfeach time it propagates or is distributed.

� Conventional signature based scanners areineffective for detecting variants of same malware.

� Sophisticated signature(s) are required to detectmetamorphic variants of malware.

Motivation

� Variants of metamorphic malware are generatedusing a small embeddedmetamorphic engine todefeat detection [2].

� Limited number of instructions are used to generate

variants so as to preserve functionality.

� Metamorphic malware like DNA/ protein sequencesmutate from generation to generation, they inheritfunctionality and some structural similarity withancestral malware.

Objective

� To devise a method for detection of metamorphicmalware and its variants.

� To extract the abstract signature(s) usingBioinformatics sequence alignment

� base code is preserved in different generations, obfuscatedusing junk code or equivalent instructions etc.

� To identify unseen malware samples using bestrepresentative signatures (group/single) of a family.

Sequence Alignment [1/2]

� Sequence alignment is a way of arrangingDNA/Protein sequences to identify regions ofsimilarity to infer functional, structural orevolutionary relationship.

� Alignment Methods

� Global Alignment - align sequences end to end.

� Local Alignment - align substring of one sequence withsubstring of other.

� Multiple Sequence Alignment (MSA) - align more thantwo sequences.

Sequence Alignment [2/2]

� Global alignmentL G P S S K Q T G K G S - S R I D N

L N - I T K S A G K G A I M R L D A

� Localalignment

� Localalignment- - - - - - T G - G - - - - - - -

- - - - - - A G K G - - - - - - -

� Alignment Parameter� Match

� Mismatch

� GapPoint of Mutation

Multiple Sequence Alignment� MSA is extension of pairwise alignment for more

than two sequences.

� It is used to identify conserved regions across agroup of sequences.

M1 M2 M3 M4 M5

add add add - add

- push push push push

Mov mov mov mov mov

- call jmp jz jmp

jmp jmp mov mov mov

• M i – ith Malware instance

Implementation of MSA

� MSA is implemented usingProgressive technique(ClustalW[9])

� Progressive MSA follows three steps:

� Determine similarity between each pair by pairwise

� Determine similarity between each pair by pairwisealignment.

� Construct aguided tree (Phylogenetic tree) to representevolutionary relationship.

� MSA is build by aligning closely related groups to mostdistant group according toguided tree.

Phylogenetic Tree

� Phylogenetic Tree depict evolutionary relationship among the sequences.

� To form groups of similar

viruses

� Guides MSA progressively

to align closer groups first

A B D F

( (E,(A,B)), (D,F) )

Similarity Measurement

� Alignment Score : Is the sum of score specifiedfor each aligned pair of mnemonics. Higher thescore more similar the sequences.

� Distance (d) : Calculated using followingformulas

formulas

Higher the distance more dissimilar the sequences

matchmismatch

mismatchNd

)##(# gapmatchmismatchLd ++=• Nd is Normalized distance, Ld is Levenshtein distance

Identification of Base Malware

� Base malware in a family is most similar to rest allwith highest sum of score using pairwise alignment(SoP[3]).

M1 M2 M3 M4 SoPM2

M1 - 7 -2 1 6

M2 7 - -3 0 4

M3 -2 -3 - 1 -4

M4 1 0 1 - 2

is Base Malware Score Matrix

• M i – ith Malware instance

Implementation Method

� MetamOrphic Malware ExploratioN TechniqueUsing MSA (MOMENTUM) demonstrate theapplicability of Bioinformatics Techniques formetamorphic malware analysis and detection.

� Two phase of MOMENTUN are:

� Analysis of Metamorphism in Tools/Real Malware

� Signature Modelling and Testing

MOMENTUM [1/2]Metamorphic Families

(Virus Tools and Real Malware)

Intra-Family pair-wise Alignment

Distance Matrix Base file Alignments of twofiles

Metamorphic?Inter-Family pair-wise

Alignment

FamiliesOverlap ?

Obfuscation ?

• Flow diagram for metamorphism analysis

MOMENTUM [2/2]

Training Set Testing Set

Divide data set in two parts

Extract Group Signature

Testing with single and group signatures

Single Signature

Scan Logs

Threshold Threshold

• Diagram depicts Signature Modelling and Testing

MSA Signature� MSA signature (single signature) is a sequence of

preserved mnemonics in alignment.

M1 M2 M3 M4 M5 MSA Sign

push push - - push push

� Mnemonic that appears more than 50% in a rowis included in MSA signature.

- - jump jump jump jump

mov mov - lea xor

call call call call call call

push mov mov - mov mov

• M i – ith Malware instance and Mt – Test Sample

Group Signature

� Group signature is extracted from single signaturefor each subgroup.

� Sub groups are formed using evolutionary relationship.

� Single signature is extracted for each subgroup andcombinedin theform of wildcard.

combinedin theform of wildcard.

� DiagramSign1 Sign2 Sign3 Sign4 Sign5 Group Sign

push push - - push push

jz jz jump jump jump jump|jz

mov mov - lea xor mov|lea|xor

call call call call call call

- mov mov - push mov|push

• Signi – Signature for ith sub-group in a family

Threshold

0 B B M M Score

. . . . . .

Benign Malware

Threshold0 Bmin Bmax Mmin Mmax

Where:Bmin Benign with minimum score

Bmax Benign with maximum score

Mmin Malware with minimum score

Mmax Malware with maximum score

Threshold (Bmax + Mmin) /2 , ( Threshold > Bmax )

Dataset [1/2]

Dataset Description:

Type Source #Family #instances

Synthetic NGVCK, PSMPC, G2,

MPCGEN46 1051

User Agencies

� * consists of unknown viruses (in test set).

� Dataset is equally divided into training andtesting set.

RealUser Agencies

52 + 1* 1209VxHeavens

Benign System32,Cygwin etc. 1 150

Dataset [2/2]

� All samples are in Portable Executables (PE)format.

� Samples are unpacked using

� Dynamicunpacker(EtherUnpack[7] )

� Signature based unpacker (GUNPacker [10])

� Malware families are created from combinedscanned results of 14 antiviruses.

� Benign samples are also scanned.

Result for Intra Family

Global

Levenshtein

� Non zero values indicates presence of metamorphism insynthetic data.

� Levenshtein distance is high due to junk code insertion.� Inspite of high values of global distance, local distances are

low in most of the samples. This indicates presence of similarregions in code.

NGVCK PSMPC G2 MPCGEN

• Average distance is between 0 to 1

Result for Inter Family

Global

Levenshtein

� Distance is less than intra family distance. This indicatesmost of malware share some base code.

� Levenshtein distance is higher because of change infunctionality.

NGVCK PSMPC G2 MPCGEN VX HEAVENS

• Average distance is between 0 to 1

Comparative Analysis

VIRUS TYPEReplacements/

AlignmentAvg. SoD OBFUSCATION

NGVCK 47 1.03 Average Simple

G2 3 1.45 Low Simple

MPCGEN 31 0.61 Average Simple

PSMPC 1 1.35 Low Weak

Vx-Heavens 122 8.3 Large Complex

� Viruses generated using tools belong to same family.� Families of real malware are distinct.� In PSMPCloop andjump instructions contribute for

obfuscation this increases the distance between samples.� NGVCK viruses overlaps with real malware (Savior).

• SoD – Sum of distances of a family with rest other family

Detection Results

MSA Single

Group Signature

� 95.5% of malware is detected with MSA signature, detectionwith Group signature is 72.4% .

� 53% of benign is falsely detected as malware with MSAsignature due to loss mnemonics used for mutation inmalware.

� Group signature preserves point of mutation that is absent inbenign samples.

TPR FPR

MOMENTUM with Antiviruses

� MOMENTUM (group signature) is found to be comparableto best ant-viruses.� Out of 35 undetected malware withantiviruses, MOMENTUM could detect 20 malware.

Scope for Improvement

� Instead of same mismatch score, computeweighted score for each pair of mnemonics usingfrequency of mismatches.

� In the alignment, operand part can be consideredto verify actualchanges(replacement/gap).

to verify actualchanges(replacement/gap).

� This can fetch the way morpher preservesfunctionality.

List of Publications[1] Vinod P., V.Laxmi, M.S.Gaur, Grijesh Chauhan

Detecting Malicious Files using Non-Signature based Methods,(To appear) Oxford Computer Journal.

[2] Vinod P., V.Laxmi, M.S.Gaur, Grijesh ChauhanMalware Detection using Non-Signature based Method, In

Malware Detection using Non-Signature based Method, InProceeding of IEEE International Conference on NetworkCommunication and Computer-ICNCC 2011, pp-427-43, DOI:978-1-4244-9551-1/11.

References[1] E.Karim, A.Walenstein, A.Lakhotia, “Malware Phylogeny using Permutation

of code”, In Proceedings of EICAR 2005, pp 167-174

[2] M.R. Chouchane and A. Lakhotia , “Using engine signature to detect metamorphic malware”, In Proceedings of the 4th ACM workshop on Recurring malcode, WORM '06, 2006,73-78.

[3] Mona Singh, " Multiple Sequence Alignment ", Lecture Notes:www.cs.princeton.edu/~mona/Lecture/msa1.pdf (Last viewed on 14-6-2011)

[4] Mona Singh, " Phylogenetics ", Lecture Notes:www.cs.princeton.edu/~mona/Lecture/msa1.pdf (Last viewed on 14-6-2011)

[5] T. Smith and M. Waterman, “Identification of Common Molecular Subsequences”, Journal of Molecular Biology, pp 195-197, 1987

[6] Mark Stamp, Wing Wong. "Hunting for metamorphic engines". Journal in Computer Virology, 2(3):211-229

References[7] Ether for Malware Unpacking: http://ether.gtisc.gatech.edu/malware.html

(Last viewed on 14-6-2011)

[8] Jian Li, Jun Xu, Ming Xu, HengiLi Zhao, Ning Zheng, “MalwareObfuscation Measuring via Evolutionary Similarity”, In Proceedings of IEEEInt. Conference on Future Information Network 2009.

[9] Larkin MA et al, " Clustal W and Clustal X version 2.0 ". Bioinformatics, 23, 2947-2948, 2007.

[10] GUnPacker : http://www.woodmann.com/collaborative/tools/index.php/GUnPacker(Last viewed on 14-6-2011)

Thanks!

metamorphic malware analysis and detection

metamorphic malware

t g g

unseen malware samples

metamorphic enginediagram

sequences end

jaipurlocal alignment

distance d

agroup of sequences

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