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Background Buffer Overflow Integer and Heap Overflow Summary
CS 6V81-05: System Security and Malicious Code Analysis
Buffer Overflow, Integer and Heap Overflow
Zhiqiang Lin
Department of Computer ScienceUniversity of Texas at Dallas
April 11th, 2012
Background Buffer Overflow Integer and Heap Overflow Summary
Outline
1 Background
2 Buffer Overflow
3 Integer and Heap Overflow
4 Summary
Outline
1 Background
2 Buffer Overflow
3 Integer and Heap Overflow
4 Summary
Background Buffer Overflow Integer and Heap Overflow Summary
IA32 Stack
Region of memorymanaged with stackdisciplineGrows toward loweraddressesRegister %esp indicateslowest stack address
address of top element
IA32 Stack
Stack Pointer %esp
Stack “Top”
Stack “Bottom”
Background Buffer Overflow Integer and Heap Overflow Summary
IA32 Stack Pushing
Pushing
pushl srcFetch operand at SrcDecrement %esp by 4Write operand ataddress given by %esp
IA32 Stack Pushing
Stack “Top”
Stack “Bottom”
Stack Pointer %esp
-4
Background Buffer Overflow Integer and Heap Overflow Summary
IA32 Stack Popping
Popping
popl destRead operand ataddress given by %espIncrement %esp by 4Write to Dest
IA32 Stack Popping
Stack Pointer %esp
Stack “Top”
Stack “Bottom”
+4
Background Buffer Overflow Integer and Heap Overflow Summary
Procedure Call Example
804854e: e8 3d 06 00 00 call 8048b90 <main>8048553: 50 pushl %eax
Carnegie Mellon
4
%esp
%eip
%esp
%eip 0x804854e
0x108
0x108
0x10c
0x110
0x104
0x804854e
123
Procedure Call Example
0x108
0x10c
0x110
123
0x108
804854e: e8 3d 06 00 00 call 8048b90 <main>
8048553: 50 pushl %eax
%eip is program counter
Background Buffer Overflow Integer and Heap Overflow Summary
Procedure Call Example
804854e: e8 3d 06 00 00 call 8048b90 <main>8048553: 50 pushl %eax
Carnegie Mellon
5
%esp
%eip
%esp
%eip 0x804854e
0x108
0x108
0x10c
0x110
0x104
0x804854e
123
Procedure Call Example
0x108
0x10c
0x110
123
0x108
call 8048b90
804854e: e8 3d 06 00 00 call 8048b90 <main>
8048553: 50 pushl %eax
%eip is program counter
Background Buffer Overflow Integer and Heap Overflow Summary
Procedure Call Example
804854e: e8 3d 06 00 00 call 8048b90 <main>8048553: 50 pushl %eax
Carnegie Mellon
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%esp
%eip
%esp
%eip 0x804854e
0x108
0x108
0x10c
0x110
0x104
0x804854e
123
Procedure Call Example
0x108
0x10c
0x110
123
0x108
call 8048b90
804854e: e8 3d 06 00 00 call 8048b90 <main>
8048553: 50 pushl %eax
0x104
%eip is program counter
Background Buffer Overflow Integer and Heap Overflow Summary
Procedure Call Example
804854e: e8 3d 06 00 00 call 8048b90 <main>8048553: 50 pushl %eax
Carnegie Mellon
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%esp
%eip
%esp
%eip 0x804854e
0x108
0x108
0x10c
0x110
0x104
0x804854e
0x8048553
123
Procedure Call Example
0x108
0x10c
0x110
123
0x108
call 8048b90
804854e: e8 3d 06 00 00 call 8048b90 <main>
8048553: 50 pushl %eax
0x104
%eip is program counter
Background Buffer Overflow Integer and Heap Overflow Summary
Procedure Call Example
804854e: e8 3d 06 00 00 call 8048b90 <main>8048553: 50 pushl %eax
Carnegie Mellon
8
%esp
%eip
%esp
%eip 0x804854e
0x108
0x108
0x10c
0x110
0x104
0x804854e
0x8048553
123
Procedure Call Example
0x108
0x10c
0x110
123
0x108
call 8048b90
804854e: e8 3d 06 00 00 call 8048b90 <main>
8048553: 50 pushl %eax
0x8048b90
0x104
%eip is program counter
Background Buffer Overflow Integer and Heap Overflow Summary
Procedure Return Example
8048591: c3 ret
Carnegie Mellon
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%esp
%eip
0x104
%esp
%eip 0x8048591 0x8048591
0x104 0x104
0x108
0x10c
0x110
0x8048553
123
Procedure Return Example
0x108
0x10c
0x110
123
ret
8048591: c3 ret
0x108
%eip is program counter
0x8048553
0x8048553
Background Buffer Overflow Integer and Heap Overflow Summary
Call Chain Example Carnegie Mellon
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Call Chain Example
Code Structure
yoo(…)
{
•
•
who();
•
•
}
who(…)
{
• • •
amI();
• • •
amI();
• • •
}
amI(…)
{
•
•
amI();
•
•
}
yoo
who
amI
amI
amI
Call Chain
Procedure amI recursive
amI
Background Buffer Overflow Integer and Heap Overflow Summary
Call Chain Example
Contents
Local variablesReturn informationTemporary space
Management
Space allocated when enter procedure
“Set-up” code
Deallocated when return
“Finish” code
Pointers
Stack pointer %esp indicates stack topFrame pointer %ebp indicates start ofcurrent frame
yoo
who
Stack Frames
amI
Background Buffer Overflow Integer and Heap Overflow Summary
Stack Operation
Stack Pointer %esp
yoo
•
•
• Frame
Pointer %ebp
yoo
Call Chain yoo(…)
{
•
•
who();
•
•
}
Background Buffer Overflow Integer and Heap Overflow Summary
Stack Operation
Stack Pointer %esp
yoo
who
•
•
•
Frame Pointer %ebp
yoo
who
Call Chain who(…)
{
• • •
amI();
• • •
amI();
• • •
}
Background Buffer Overflow Integer and Heap Overflow Summary
Stack Operation
Stack Pointer %esp
yoo
who
amI
•
•
•
Frame Pointer %ebp
yoo
who
amI
Call Chain amI(…)
{
•
•
amI();
•
•
}
Background Buffer Overflow Integer and Heap Overflow Summary
Stack Operation
Stack Pointer %esp
yoo
who
amI
•
•
•
Frame Pointer %ebp
yoo
who
amI
Call Chain amI(…)
{
•
•
amI();
•
•
}
amI
amI
Background Buffer Overflow Integer and Heap Overflow Summary
Stack Operation
Stack Pointer %esp
yoo
who
amI
•
•
•
Frame Pointer %ebp
yoo
who
amI
Call Chain amI(…)
{
•
•
amI();
•
•
}
amI
amI
amI
amI
Background Buffer Overflow Integer and Heap Overflow Summary
Stack Operation
Stack Pointer %esp
yoo
who
amI
•
•
•
Frame Pointer %ebp
yoo
who
amI
Call Chain amI(…)
{
•
•
amI();
•
•
}
amI
amI
amI
Background Buffer Overflow Integer and Heap Overflow Summary
Stack Operation
Stack Pointer %esp
yoo
who
amI
•
•
•
Frame Pointer %ebp
yoo
who
amI
Call Chain amI(…)
{
•
•
amI();
•
•
}
amI
amI
Background Buffer Overflow Integer and Heap Overflow Summary
Stack Operation
Stack Pointer %esp
yoo
who
•
•
•
Frame Pointer %ebp
yoo
who
Call Chain who(…)
{
• • •
amI();
• • •
amI();
• • •
} amI
amI
amI
Background Buffer Overflow Integer and Heap Overflow Summary
Stack Operation
Stack Pointer %esp
yoo
who
amI
•
•
•
Frame Pointer %ebp
yoo
who
Call Chain amI(…)
{
•
•
•
•
} amI
amI
amI
amI
Background Buffer Overflow Integer and Heap Overflow Summary
Stack Operation
Stack Pointer %esp
yoo
who
•
•
•
Frame Pointer %ebp
yoo
who
Call Chain who(…)
{
• • •
amI();
• • •
amI();
• • •
} amI
amI
amI
amI
Background Buffer Overflow Integer and Heap Overflow Summary
Stack Operation
yoo(…)
{
•
•
who();
•
•
}
Stack Pointer %esp
yoo
•
•
• Frame
Pointer %ebp
yoo
who
Call Chain
amI
amI
amI
amI
Background Buffer Overflow Integer and Heap Overflow Summary
IA32/Linux Stack Frame
Current Stack Frame (“Top” toBottom)
Parameters for function aboutto call
“Argument build”
Local variables
If can’t keep in registers
Saved register contextOld frame pointer
Caller Stack Frame
Return address
Pushed by callinstruction
Arguments for this call
Carnegie Mellon
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IA32/Linux Stack Frame
Current Stack Frame (“Top” to Bottom) Parameters for function about to
call
“Argument build”
Local variables
If can’t keep in registers
Saved register context
Old frame pointer
Caller Stack Frame Return address
Pushed by call instruction
Arguments for this call Stack Pointer (%esp)
Frame Pointer (%ebp)
Return Addr
Saved
Registers
+
Local
Variables
Argument
Build
Old %ebp
Arguments
Caller
Frame
Background Buffer Overflow Integer and Heap Overflow Summary
IA32 Linux Memory Layout
Stack
Runtime stack (8MB limit)E. g., local variables
Heap
Dynamically allocated storageWhen call malloc(), calloc(),new()
Data
Statically allocated dataE.g., arrays & strings declaredin code
Text
Executable machineinstructionsRead-only
Upper 2 hex digits = 8 bits of address
FF
00
Stack
Text
Data
Heap
08
8MB
not drawn to scale
Background Buffer Overflow Integer and Heap Overflow Summary
Memory Allocation Example
char big_array[1<<24]; /* 16 MB */char huge_array[1<<28]; /* 256 MB*/
int beyond;char *p1, *p2, *p3, *p4;
int useless() { return 0; }
int main(){p1 = malloc(1 <<28); /* 256 MB */p2 = malloc(1 << 8); /* 256 B */p3 = malloc(1 <<28); /* 256 MB */p4 = malloc(1 << 8); /* 256 B *//* Some print statements ... */}
Where does everything go?
FF
00
Stack
Text
Data
Heap
08
not drawn to scale
Where does everything go?
Background Buffer Overflow Integer and Heap Overflow Summary
IA32 Example AddressesCarnegie Mellon
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IA32 Example Addresses
$esp 0xffffbcd0
p3 0x65586008
p1 0x55585008
p4 0x1904a110
p2 0x1904a008
&p2 0x18049760
&beyond 0x08049744
big_array 0x18049780
huge_array 0x08049760
main() 0x080483c6
useless() 0x08049744
final malloc() 0x006be166
address range ~232
FF
00
Stack
Text
Data
Heap
08
80
not drawn to scale
malloc() is dynamically linked
address determined at runtime
FF
00
Stack
Text
Data
Heap
08
80
not drawn to scale
Outline
1 Background
2 Buffer Overflow
3 Integer and Heap Overflow
4 Summary
Background Buffer Overflow Integer and Heap Overflow Summary
Internet Worm and IM War
November, 1988
Internet Worm attacks thousands of Internet hosts.How did it happen?
Background Buffer Overflow Integer and Heap Overflow Summary
Internet Worm and IM War
November, 1988Internet Worm attacks thousands of Internet hosts.How did it happen?
July, 1999Microsoft launches MSN Messenger (instant messagingsystem).Messenger clients can access popular AOL InstantMessaging Service (AIM) servers
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Internet Worm and IM War
November, 1988 Internet Worm attacks thousands of Internet hosts.
How did it happen?
July, 1999 Microsoft launches MSN Messenger (instant messaging system).
Messenger clients can access popular AOL Instant Messaging Service (AIM) servers
AIM server
AIM client
AIM client
MSN client
MSN server
Background Buffer Overflow Integer and Heap Overflow Summary
Internet Worm and IM War (cont.)
August 1999
Mysteriously, Messenger clients can no longer access AIMservers.Microsoft and AOL begin the IM war:
AOL changes server to disallow Messenger clientsMicrosoft makes changes to clients to defeat AOL changes.At least 13 such skirmishes.
How did it happen?
The Internet Worm and AOL/Microsoft War were bothbased on stack buffer overflow exploits!
many library functions do not check argument sizes.allows target buffers to overflow.
Background Buffer Overflow Integer and Heap Overflow Summary
String Library Code
Implementation of Unix function gets()
/* Get string from stdin */char *gets(char *dest){
int c = getchar();char *p = dest;while (c != EOF && c != ’\n’) {
*p++ = c;c = getchar();
}
*p = ’\0’;return dest;
}
No way to specify limit on number of characters to read
Similar problems with other library functions
strcpy, strcat: Copy strings of arbitrary lengthscanf, fscanf, sscanf, when given %s conversionspecification
Background Buffer Overflow Integer and Heap Overflow Summary
Vulnerable Buffer Code
/* Echo Line */void echo(){
char buf[4]; /* Way too small! */gets(buf);puts(buf);
}
void call_echo() {echo();
}
unix>./bufdemoType a string:12345671234567
unix>./bufdemoType a string:12345678Segmentation Fault
unix>./bufdemoType a string:123456789ABCSegmentation Fault
Background Buffer Overflow Integer and Heap Overflow Summary
Buffer Overflow Disassembly
echo80485c5: 55 push %ebp80485c6: 89 e5 mov %esp,%ebp80485c8: 53 push %ebx80485c9: 83 ec 14 sub $0x14,%esp80485cc: 8d 5d f8 lea 0xfffffff8(%ebp),%ebx80485cf: 89 1c 24 mov %ebx,(%esp)80485d2: e8 9e ff ff ff call 8048575 <gets>80485d7: 89 1c 24 mov %ebx,(%esp)80485da: e8 05 fe ff ff call 80483e4 <puts@plt>80485df: 83 c4 14 add $0x14,%esp80485e2: 5b pop %ebx80485e3: 5d pop %ebp80485e4: c3 ret
call echo80485eb: e8 d5 ff ff ff call 80485c5 <echo>80485f0: c9 leave80485f1: c3 ret
Background Buffer Overflow Integer and Heap Overflow Summary
Buffer Overflow Stack
Buffer Overflow Stack
/* Echo Line */
void echo()
{
char buf[4]; /* Way too small! */
gets(buf);
puts(buf);
}
Return Address
Saved %ebp %ebp
Stack Frame for main
Stack Frame for echo
[3] [2] [1] [0] buf
Before call to gets
Saved %ebx
/* Echo Line */void echo(){
char buf[4]; /* Way too small! */gets(buf);puts(buf);
}
echo:pushl %ebp # Save %ebp on stackmovl %esp, %ebppushl %ebx # Save %ebxsubl $20, %esp # Allocate stack spaceleal -8(%ebp),%ebx # Compute buf as %ebp-8movl %ebx, (%esp) # Push buf on stackcall gets # Call gets. . .
Background Buffer Overflow Integer and Heap Overflow Summary
Buffer Overflow Stack Example
unix> gdb bufdemo(gdb) break echoBreakpoint 1 at 0x80485c9(gdb) runBreakpoint 1, 0x80485c9 in echo ()(gdb) print /x $ebp$1 = 0xffffd678(gdb) print /x *(unsigned *)$ebp$2 = 0xffffd688(gdb) print /x *((unsigned *)$ebp + 1)$3 = 0x80485f0
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Buffer Overflow Stack Example
unix> gdb bufdemo
(gdb) break echo
Breakpoint 1 at 0x80485c9
(gdb) run
Breakpoint 1, 0x80485c9 in echo ()
(gdb) print /x $ebp
$1 = 0xffffd678
(gdb) print /x *(unsigned *)$ebp
$2 = 0xffffd688
(gdb) print /x *((unsigned *)$ebp + 1)
$3 = 0x80485f0
80485eb: e8 d5 ff ff ff call 80485c5 <echo>
80485f0: c9 leave
0xffffd678
buf
0xffffd688
Return Address
Saved %ebp
Stack Frame for main
Stack Frame for echo
[3] [2] [1] [0]
Stack Frame for main
Stack Frame for echo
xx xx xx xx buf
ff ff d6 88
08 04 85 f0
Before call to gets Before call to gets
Saved %ebx Saved %ebx
Background Buffer Overflow Integer and Heap Overflow Summary
Buffer Overflow Stack Example #1Carnegie Mellon
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Buffer Overflow Example #1
Overflow buf, and corrupt %ebx, but no problem
Stack Frame for echo
xx xx xx xx buf
Stack Frame for echo
34 33 32 31 buf
00 37 36 35
Before call to gets Input 1234567
0xffffd678
0xffffd688 Stack Frame for main
ff ff d6 88
08 04 85 f0
0xffffd678
0xffffd688 Stack Frame for main
ff ff d6 88
08 04 85 f0
Saved %ebx
Background Buffer Overflow Integer and Heap Overflow Summary
Buffer Overflow Stack Example #2Carnegie Mellon
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Buffer Overflow Example #2
Base pointer corrupted
Stack Frame for echo
xx xx xx xx buf
Stack Frame for echo
34 33 32 31 buf
00
38 37 36 35
Before call to gets Input 12345678
. . .
80485eb: e8 d5 ff ff ff call 80485c5 <echo>
80485f0: c9 leave # Set %ebp to corrupted value
80485f1: c3 ret
0xffffd678
0xffffd688 Stack Frame for main
ff ff d6 88
08 04 85 f0
0xffffd678
0xffffd688 Stack Frame for main
ff ff d6
08 04 85 f0
Saved %ebx
Background Buffer Overflow Integer and Heap Overflow Summary
Buffer Overflow Stack Example #3Carnegie Mellon
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Buffer Overflow Example #3
Return address corrupted
Stack Framefor echo
xx xx xx xx buf
Stack Framefor echo
34 33 32 31 buf
43 42 41 3900
38 37 36 35
Before call to gets Input 123456789!”#
80485eb: e8 d5 ff ff ff call 80485c5 <echo>80485f0: c9 leave # Desired return point
0xffffd678
0xffffd688Stack Framefor main
ff ff d6 8808 04 85 f0
0xffffd678
0xffffd688Stack Framefor main
08 04 85
Saved %ebx
Background Buffer Overflow Integer and Heap Overflow Summary
Buffer Overflow Stack Example #3Carnegie Mellon
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Malicious Use of Buffer Overflow
Input string contains byte representation of executable code
Overwrite return address A with address of buffer B
When bar() executes ret, will jump to exploit code
int bar() {
char buf[64];
gets(buf);
...
return ...;
}
void foo(){
bar();
...
}
Stack after call to gets()
B
return address A
foo stack frame
bar stack frame
B
exploit code
pad data written by gets()
Input string contains byte representation of executablecodeOverwrite return address A with address of buffer BWhen bar() executes ret, will jump to exploit code
Background Buffer Overflow Integer and Heap Overflow Summary
Exploits Based on Buffer Overflows
Buffer overflow bugs allow remote machines to executearbitrary code on victim machinesInternet worm
Early versions of the finger server (fingerd) used gets() toread the argument sent by the client:Worm attacked fingerd server by sending phony argument:
finger “exploit-code padding new-return-address”exploit code: executed a root shell on the victim machinewith a direct TCP connection to the attacker.
Background Buffer Overflow Integer and Heap Overflow Summary
Exploits Based on Buffer Overflows
Buffer overflow bugs allow remote machines to executearbitrary code on victim machinesIM War
AOL exploited existing buffer overflow bug in AIM clientsexploit code: returned 4-byte signature (the bytes at somelocation in the AIM client) to server.When Microsoft changed code to match signature, AOLchanged signature location.
Background Buffer Overflow Integer and Heap Overflow Summary
Code Red Exploit Code
Starts 100 threads runningSpread self
Generate random IP addresses & send attack stringBetween 1st & 19th of month
Attack www.whitehouse.govSend 98,304 packets; sleep for 4-1/2 hours; repeat
Denial of service attack
Between 21st & 27th of month
Deface server’s home pageAfter waiting 2 hours
Background Buffer Overflow Integer and Heap Overflow Summary
Avoiding Overflow Vulnerability
/* Echo Line */void echo(){
char buf[4]; /* Way too small! */gets(buf);puts(buf);
}
Use library routines that limit string lengths
fgets instead of getsstrncpy instead of strcpyDon’t use scanf with %s conversion specification
Use fgets to read the stringOr use %ns where n is a suitable integer
Background Buffer Overflow Integer and Heap Overflow Summary
System-Level Protections
Randomized stack offsets
At start of program, allocaterandom amount of space on stackMakes it difficult for hacker topredict beginning of inserted code
Nonexecutable code segments
In traditional x86, can mark regionof memory as either “read-only” or“writeable”
Can execute anything readable
X86-64 added explicit “execute”permission
unix> gdb bufdemo(gdb) break echo
(gdb) run(gdb) print /x $ebp$1 = 0xffffc638
(gdb) run(gdb) print /x $ebp$2 = 0xffffbb08
(gdb) run(gdb) print /x $ebp$3 = 0xffffc6a8
Background Buffer Overflow Integer and Heap Overflow Summary
Stack Canaries
Idea
Place special value (“canary”) on stack just beyond bufferCheck for corruption before exiting function
GCC Implementation
-fstack-protector-fstack-protector-all
unix>./bufdemo-protectedType a string:12341234
unix>./bufdemo-protectedType a string:12345
*** stack smashing detected ***
Background Buffer Overflow Integer and Heap Overflow Summary
Protected Buffer Disassembly
echo804864d: 55 push %ebp804864e: 89 e5 mov %esp,%ebp8048650: 53 push %ebx8048651: 83 ec 14 sub $0x14,%esp8048654: 65 a1 14 00 00 00 mov %gs:0x14,%eax804865a: 89 45 f8 mov %eax,0xfffffff8(%ebp)804865d: 31 c0 xor %eax,%eax804865f: 8d 5d f4 lea 0xfffffff4(%ebp),%ebx8048662: 89 1c 24 mov %ebx,(%esp)8048665: e8 77 ff ff ff call 80485e1 <gets>804866a: 89 1c 24 mov %ebx,(%esp)804866d: e8 ca fd ff ff call 804843c <puts@plt>8048672: 8b 45 f8 mov 0xfffffff8(%ebp),%eax8048675: 65 33 05 14 00 00 00 xor %gs:0x14,%eax804867c: 74 05 je 8048683 <echo+0x36>804867e: e8 a9 fd ff ff call 804842c <FAIL>8048683: 83 c4 14 add $0x14,%esp8048686: 5b pop %ebx8048687: 5d pop %ebp8048688: c3 ret
Background Buffer Overflow Integer and Heap Overflow Summary
Setting Up Canary
Setting Up Canary
echo:
. . .
movl %gs:20, %eax # Get canary
movl %eax, -8(%ebp) # Put on stack
xorl %eax, %eax # Erase canary
. . .
/* Echo Line */
void echo()
{
char buf[4]; /* Way too small! */
gets(buf);
puts(buf);
} Return Address
Saved %ebp %ebp
Stack Frame for main
Stack Frame for echo
[3] [2] [1] [0] buf
Before call to gets
Saved %ebx
Canary
/* Echo Line */void echo(){
char buf[4]; /* Way too small! */gets(buf);puts(buf);
}
echo:. . .movl %gs:20, %eax # Get canarymovl %eax, -8(%ebp) # Put on stackxorl %eax, %eax # Erase canary. . .
Background Buffer Overflow Integer and Heap Overflow Summary
Checking Canary
Setting Up Canary
echo:
. . .
movl %gs:20, %eax # Get canary
movl %eax, -8(%ebp) # Put on stack
xorl %eax, %eax # Erase canary
. . .
/* Echo Line */
void echo()
{
char buf[4]; /* Way too small! */
gets(buf);
puts(buf);
} Return Address
Saved %ebp %ebp
Stack Frame for main
Stack Frame for echo
[3] [2] [1] [0] buf
Before call to gets
Saved %ebx
Canary
/* Echo Line */void echo(){
char buf[4]; /* Way too small! */gets(buf);puts(buf);
}
echo:. . .movl -8(%ebp), %eax # Retrieve from stackxorl %gs:20, %eax # Compare with Canaryje .L24 # Same: skip aheadcall __stack_chk_fail # ERROR.L24:. . .
Background Buffer Overflow Integer and Heap Overflow Summary
Canary ExampleCarnegie Mellon
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Canary Example
(gdb) break echo
(gdb) run
(gdb) stepi 3
(gdb) print /x *((unsigned *) $ebp - 2)
$1 = 0x3e37d00
Return Address
Saved %ebp %ebp
Stack Frame for main
Stack Frame for echo
[3] [2] [1] [0] buf
Before call to gets
Saved %ebx
03 e3 7d 00
Return Address
Saved %ebp %ebp
Stack Frame for main
Stack Frame for echo
buf
Input 1234
Saved %ebx
03 e3 7d 00
34 33 32 31
Benign corruption! (allows programmers to make silent off-by-one errors)
Outline
1 Background
2 Buffer Overflow
3 Integer and Heap Overflow
4 Summary
Background Buffer Overflow Integer and Heap Overflow Summary
What are the common features of integer overflowvulnerabilities?
Carnegie Mellon
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What are the common features of integer overflow vulnerabilities?
unsigned int x = read_int();
if ( x > 0x7fffffff )
abort();
unsigned int s = x*sizeof(int);
char* p=malloc(s);
read_int_into_buf(p, x);
an untrusted source
an incomplete
check
an integer overflow
a sensitive
operation a heap overflow
followed
Background Buffer Overflow Integer and Heap Overflow Summary
CVE-2008-5238(Xine)
Carnegie Mellon
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CVE-2008-5238(Xine)
……
if (version == 4) {
const uint16_t sps = _X_BE_16 (this->header+44) ? : 1;
this->w = _X_BE_16 (this->header+42);
this->h = _X_BE_16 (this->header+40);
this->cfs = _X_BE_32 (this->header+24);
this->frame_len = this->w * this->h;
this->frame_size = this->frame_len * sps;
this->frame_buffer = calloc(this->frame_size, 1);
……
an untrusted source
a sensitive
operation
Background Buffer Overflow Integer and Heap Overflow Summary
CVE-2008-1722(CUPS)
Carnegie Mellon
55
55
png_get_IHDR(pp, info, &width, &height, &bit_depth, &color_type,
&interlace_type, &compression_type, &filter_type);
{
……
if (width == 0 || width > CUPS_IMAGE_MAX_WIDTH ||
height == 0 || height > CUPS_IMAGE_MAX_HEIGHT)
{//error
return (1);
}
img->xsize = width;
img->ysize = height;
……
if (color_type == PNG_COLOR_TYPE_GRAY ||color_type ==
PNG_COLOR_TYPE_GRAY_ALPHA)
in = malloc(img->xsize * img->ysize);
else
in = malloc(img->xsize * img->ysize * 3);
……
}
an untrusted source
an incomplete
check
an integer overflow
a sensitive
operation
Background Buffer Overflow Integer and Heap Overflow Summary
CVE-2008-2430(VLC)Carnegie Mellon
56
……
if( ChunkFind( p_demux, "fmt ", &i_size ) )
{
msg_Err( p_demux, "cannot find 'fmt ' chunk" );
goto error;
}
if( i_size < sizeof( WAVEFORMATEX ) - 2 )
{
msg_Err( p_demux, "invalid 'fmt ' chunk" );
goto error;
}
stream_Read( p_demux->s, NULL, 8 ); /* Cannot fail */
/* load waveformatex */
p_wf_ext = malloc( __EVEN( i_size ) + 2 );
……
an untrusted source
an incomplete
check
an integer overflow
a sensitive
operation
Background Buffer Overflow Integer and Heap Overflow Summary
What’s the essential feature of integer overflowvulnerabilities?
Carnegie Mellon
57
What’s the essential feature of integer overflow vulnerabilities?
unsigned int x = read_int();
if ( x > 0x7fffffff )
abort();
unsigned int s = x*sizeof(int);
char* p=malloc(s);
read_int_into_buf(p, x);
an integer overflow
an untrusted source
an incomplete
check
a sensitive
operation
Outline
1 Background
2 Buffer Overflow
3 Integer and Heap Overflow
4 Summary
Background Buffer Overflow Integer and Heap Overflow Summary
Summary
Software vulnerabilities1 Cannot be avoided (software complexity)2 Memory bugs (buffer overflow, integer overflow) are
dangerous3 Tons of research has been carried out to stop memory
bugs4 Stack, and integer and heap overflow can be stopped.
Background Buffer Overflow Integer and Heap Overflow Summary
References
http://en.wikipedia.org/wiki/Buffer_overflowSmashing the Stack for Fun and Profit by Aleph OneA Comparison of Buffer Overflow PreventionImplementations and Weaknesses (Blackhat 2004)http://www.cs.cmu.edu/afs/cs/academic/class/15213-f10/www/lectures/08-machine-advanced.pdf...
