Effective flowgraph-based malware variant detection

EFFECTIVE FLOWGRAPH-
BASED MALWARE VARIANT
DETECTION
Silvio Cesare, Ph.D. Candidate, Deakin University
http://www.foocodechu.com
silvio.cesare@gmail.com

WHO AM I AND WHERE DID THIS TALK
COME FROM?
 Ph.D. Student at Deakin University.

 Research interests include:
 Automated vulnerability discovery.
 Software similarity and classification.
 Malware detection.

 This presentation is based on my malware
research.

OUTLINE
1. Introduction (you might already know this)

2. New approaches to flowgraph-based
classification

3. Evaluation

4. Other things we use our system on.

5. Conclusion

INTRODUCTION
This is to make sure everyone is up to speed.
If you’ve been to my presentations before, you
might have already seen it.

INTRODUCTION
 Malware a significant problem.
 Static detection of malware a dominant real-time
technique.
 Detecting unknown variants from known
samples very useful. Roron.ao
Klez.a Roron.b
Klez.b Roron.d
Klez.c Roron.e
Klez.d Roron.f
... ...

SIGNATURES AND BIRTHMARKS
 A birthmark is an invariant property in related
samples.

 Birthmark comparison should allow inexact
matching.

LIMITATIONS OF EXISTING
BIRTHMARKS
 Byte-level content can change in every variant.

 Comparing birthmarks often exact matching
only.

 Inefficient for inexact database searching.

 Unable to detect unknown variants of known
samples.

 Program structure a better birthmark.

THE SOFTWARE SIMILARITY
PROBLEM

THE SOFTWARE SIMILARITY
SEARCH
 Need a dissimilarity or distance metric.
 “Metric” property allows efficient database
search. Query Benign

r
q
d(p,q)
p
Query Malicious
Query

Malware

EXISTING APPROACHES: A CALL GRAPH
BIRTHMARK
 Inter-procedureal control flow.

AN OPTIMAL DISSIMILARITY METRIC
FOR GRAPHS
 Graph edit distance.

 Number of operations to transform one graph to
another.

 Complexity in NP.

 Non optimal solutions possible in cubic time.

OUR APPROACH: A SET OF CONTROL
FLOW GRAPHS BIRTHMARK
 Intra-procedural control flow.
 Many procedures.

TRANSFORMING GRAPH DISSIMILARITY
TO A STRING DISSIMILARITY PROBLEM
 Decompile control flow graphs to strings.
 Compare strings using ‘string metrics’.
proc (){
L_0 W|IEH}R
L_0:
while (v1 || v2) {
L_3 L_1:
if (v3) {
true L_2:
L_6
} else {
true L_4:
}
L_1 L_7 L_5:
true }
true L_7:
return ;
L_2 L_4
}
true

L_5

NEW APPROACHES TO
FLOWGRAPH-BASED
CLASSIFICATION

TRANSFORMING A SET OF STRINGS
PROBLEM INTO A STRING PROBLEM
 Decompiled CFGs give us a set of strings.
R W|IEH}R

 Order and concatenate strings. W|IEH}R R

W|IEH}RZ
RZ
W|}R W|}R W|}RZ

 Deliminate substrings with ‘Z’.
IEHRZ
SRZ

IEHR IEHR

 Order based on metrics. SR SR

 Number of instructions in procedure.
 Number of basic blocks.
 etc

WHAT WE TRIED (AND ENDED UP NOT
USING)
 String metrics:

 Edit distance  ed(“hello”, “ggello”) = 2

C ( xy ) −min{C ( x), (C , y )}
 Normalized Compression Distance  NCD ( x, y ) =
max{C ( x), C ( y )}

A K TKT K
 Sequence alignment  | | | | |
ATKTT T K
 All databases indexed using metric trees.

SEQUENCE ALIGNMENT WITH
BLAST
 A heuristic genome sequence search tool.

 Local sequence alignment.

 Hugely popular in bioinformatics.

 So.. transform our strings into genome
sequences.

 Then, do a genome search.

GENOME SEQUENCE EXTRACTION
proc (){
L_0 W|IEH}R
L_0:
while (v1 || v2) {
L_3 L_1:
if (v3) {
true L_2:
L_6
} else {
true L_4:
}

 ACGTRYKMACGTRYKM
L_1 L_7 L_5:
true }
true L_7:
return ;
L_2 L_4
}
true

L_5

L_0
proc (){
L_0:
W|IEH}R
A = Adeline
while (v1 || v2) {

true

true
L_3

L_6
L_1:

L_2:

L_4:
if (v3) {

} else {
C = Cytosine
G = Guanine
}
L_1 L_7 L_5:
true }
true L_7:
return ;
L_2 L_4
}

T = Thyamine
true

L_5

...

WHY DIDN’T WE USE THOSE
APPROACHES?
 Not optimally effective.

 Too slow.

 Best speed was using NCD.

A DISSIMILARITY METRIC FOR SETS OF
STRINGS (WHAT WE ENDED UP USING)
 Find a mapping between strings to minimize the
sum of distances.
p
d=ed(p,q)
q
BR

BW|{B}BR
BR
BI{B}BR
BW|{B}BR
BSSR
BSSR
BSR
BSSSR

COMBINATORIAL OPTIMISATION: THE
ASSIGNMENT PROBLEM
 Finding a minimum cost mapping is known as
the “assignment problem”

 Optimal solutions exist in cubic time.

 “Greedy” heuristic solutions faster.

 Has the properties of a metric.

IMPLEMENTATION
 Malwise system is 100,000 lines of code of C++.

 The modules for this work < 3000 lines of code.

 Unpacks malware using an application level
emulator (Ruxcon 2010)

 Pre-filtering stage to quickly cull non matching
variants (Ruxcon 2011)

EVALUATION - EFFECTIVENESS
 Calculated similarity between Roron malware
variants.

 Compared results to Ruxcon 2010 work.

 In tables, highlighted cells indicates a positive
match.

 The more matches the more effective it is.

EVALUATION - EFFECTIVENESS
ao b d e g k m q a ao b d e g k m q a
ao 0.44 0.28 0.27 0.28 0.55 0.44 0.44 0.47 ao 0.70 0.28 0.28 0.27 0.75 0.70 0.70 0.75
b 0.44 0.27 0.27 0.27 0.51 1.00 1.00 0.58 b 0.74 0.31 0.34 0.33 0.82 1.00 1.00 0.87
d 0.28 0.27 0.48 0.56 0.27 0.27 0.27 0.27 d 0.28 0.29 0.50 0.74 0.29 0.29 0.29 0.29
e 0.27 0.27 0.48 0.59 0.27 0.27 0.27 0.27 e 0.31 0.34 0.50 0.64 0.32 0.34 0.34 0.33
g 0.28 0.27 0.56 0.59 0.27 0.27 0.27 0.27 g 0.27 0.33 0.74 0.64 0.29 0.33 0.33 0.30
k 0.55 0.51 0.27 0.27 0.27 0.51 0.51 0.75 k 0.75 0.82 0.29 0.30 0.29 0.82 0.82 0.96
m 0.44 1.00 0.27 0.27 0.27 0.51 1.00 0.58 m 0.74 1.00 0.31 0.34 0.33 0.82 1.00 0.87
q 0.44 1.00 0.27 0.27 0.27 0.51 1.00 0.58 q 0.74 1.00 0.31 0.34 0.33 0.82 1.00 0.87
a 0.47 0.58 0.27 0.27 0.27 0.75 0.58 0.58 a 0.75 0.87 0.30 0.31 0.30 0.96 0.87 0.87

Exact Matching Heuristic Approximate
(Ruxcon 2010) Matching (Ruxcon 2010)
ao b d e g k m q a
ao 0.86 0.49 0.54 0.50 0.87 0.86 0.86 0.86
b 0.87 0.57 0.63 0.62 0.96 1.00 1.00 0.96
d 0.61 0.64 0.85 0.91 0.64 0.64 0.64 0.64
e 0.64 0.69 0.85 0.90 0.68 0.69 0.69 0.68
g 0.62 0.68 0.91 0.91 0.68 0.68 0.68 0.68
k 0.88 0.96 0.58 0.62 0.61 0.96 0.96 0.99
m 0.87 1.00 0.57 0.63 0.62 0.96 1.00 0.96
q 0.87 1.00 0.57 0.63 0.62 0.96 1.00 0.96
a 0.87 0.96 0.58 0.62 0.61 0.99 0.96 0.96

Assignment problem

EVALUATION – FALSE POSITIVES
 Database of 10,000 malware.

 Scanned 1,601 benign binaries.

 7 false positives. Less than 1%.

 Very small binaries have small signatures and
cause weak matching.

EVALUATION - EFFICIENCY
 Median benign and malware processing time is
0.06s and 0.84s.
Malware
% Samples Benign Time(s)
Time(s)
10 0.02 0.16
20 0.02 0.28
30 0.03 0.30
40 0.03 0.36
50 0.06 0.84
60 0.09 0.94
70 0.13 0.97
80 0.25 1.03
90 0.56 1.31
100 8.06 585.16

BUT THAT’S NOT ALL WE
USE THE MALWISE ENGINE
FOR..

SIMSEER – A SOFTWARE SIMILARITY
WEB SERVICE
 An online service to identify similarity between
programs
 Based on Malwise.
 Renders an evolutionary tree to show program
relationships.
 Free to use!
 http://www.foocodechu.com/?q=simseer-a-software-similarit

Effective flowgraph-based malware variant detection

SIMSEER - DEMO
 http://www.youtube.com/watch?v=ymo7DKlKCH4

BUGWISE
 Automatically detect bugs and vulnerabilities in
Linux executable binaries.
 Uses static program analysis from Malwise.
 Decompilation
 Data Flow Analysis 

 Free to use!
 http://www.foocodechu.com/?q=bugwise-a-bug-detection-we

BUGWISE – SGID GAMES XONIX BUG IN
DEBIAN LINUX
memset(score_rec[i].login, 0, 11);

strncpy(score_rec[i].login, pw->pw_name, 10);

memset(score_rec[i].full, 0, 65);

strncpy(score_rec[i].full, fullname, 64);

score_rec[i].tstamp = time(NULL);

free(fullname);

if((high = freopen(PATH_HIGHSCORE, "w",high)) == NULL) {

fprintf(stderr, "xonix: cannot reopen high score filen");

free(fullname);
gameover_pending = 0;

return;

}

PUBLICATIONS
 Book published by Springer.
 http://www.springer.com/computer/security+and+
cryptology/book/978-1-4471-2908-0

CONCLUSION
 Malwise effectively identifies malware variants.

 Runs in real-time in expected case.

 Large functional code base and years of
development time.

 Happy to talk to vendors.

 http://www.FooCodeChu.com

Effective flowgraph-based malware variant detection

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