[PDF] [PDF] Format Strings Shellcode and Stack Protection - UCSD CSE





Previous PDF Next PDF



Windows 2000 Format String Vulnerabilities

formatted in by printf'ing a format string to a variable. To clarify: For example on Intel



Exploiting Format String Vulnerabilities

1 sept. 2001 In normal buffer overflows we overwrite the return address of a function frame on the stack. As the function that owns this frame returns it ...



Low Level Software Security II: Format Strings Shellcode

https://cseweb.ucsd.edu/classes/sp18/cse127-b/cse127sp18.4.pdf



Untitled

22 mar. 2017 started format strings exploits ... format string overwrite: setup ... buffer starts 16 bytes above printf return address.



Format String & Double-Free Attacks

argument pointer points to the front of your format string. › Put a %n at the end and overwrite the return address to point at the shellcode in the buffer.



Cornell CS

15 feb. 2001 The exploitation of format string bugs represents a new technique for ... overwrite return addresses on the stack internal linkage tables ...



Return-to-libc

if we overwrite the return address with an address to a function in a libc library and overwriting the Remember in the format strings exploit tutorial.



Raluca Popa Spring 2018 CS 161 Computer Security Discussion 1

22 ian. 2018 A format-string vulnerability can allow an attacker to overwrite a saved return address even when stack canaries are enabled. 3. If you have ...



Advanced Format String Attacks

perform string formatting leading to the potential to Point format string at overwrite address and write address of shellcode to end of string.



Attacking the stack

Format string attacks were only discovered (invented?) in 2000 2. overwriting the return address on the stack to this place where the shell code is.



[PDF] Format Strings Shellcode and Stack Protection - UCSD CSE

Format String Vulnerabilities: Writing ? Value that we really want to overwrite is likely a pointer (like the return address)



[PDF] Exploiting Format String Vulnerabilities - CS155

1 sept 2001 · In normal buffer overflows we overwrite the return address of a function frame on the stack As the function that owns this frame returns it 



[PDF] Format String Vulnerability printf ( user input ); - Syracuse University

The function retrieves the parameters requested by the format string from the stack printf ("a has value d b has value d c is at address: 08x\n"



[PDF] Format Strings

“Format strings” are the control strings that are passed to the printf() global canary or overwriting a return address without touching the canary



[PDF] Format-String Vulnerability - Fengwei Zhang

printf() scans the format string and prints out each character until “ ” is encountered Goal : To modify the return address of the vulnerable code



[PDF] slides

1 avr 2017 · started format strings exploits format string overwrite: setup buffer starts 16 bytes above printf return address



[PDF] Blind Format String Attacks - Technische Universität München

tion we show a way to exploit format string vulnerabilities on the heap overwrite everything between this buffer and the return address



[PDF] Format String Vulnerabilities

26 fév 2019 · Nice Arbitrary Code Execution It's hard to overwrite the return address like in a buffer overflow Instead we overwrite a entry 



[PDF] Format String & Double-Free Attacks - Repository [Root Me

A simple format string vulnerability: snprintf copies data from the format string until it reaches a ' ' Overwriting the Return Address



[PDF] Format String Vulnerabilities and Exploitation - NCC Group Research

Windows 2000 Format String Vulnerabilities By David Litchfield For example on Intel they could overwrite a saved return address

  • What is a format string vulnerability?

    What is a Format String Vulnerability? Often found in C language programs, it refers to a bug found in the printf() function. It is widely used to transport data, which could be ASCII text strings, to the standard output. When used properly, text strings can lead to effective and automated conversion types.
  • While buffer overflow attacks exist due to failure to perform stable bounds checks, format string attacks exist when a developer fails to perform reliable input validation checks.

CSE 127 Computer Security

Alex Gantman, Spring 2018, Lecture 4

Low Level Software Security II:Format Strings, Shellcode, & Stack Protection

Review

variables are stored on the stack

ŷNext to control flow data like the

return address and saved frame pointer variables are accessed by providing relative to the frame pointer saved fp saved fp ret addr argi+2 argi+1 argi argi+2argi+1 argiret addr local 1local 2local 3local 4 low address high address

Calleeframe

Caller frame

fp sp Stack

Review

the caller and the calleeabout the number, size, and ordering of function arguments.

ŷ#include function declaration

declaration differs from actual implementation?

ŷIf the function is called with more

or fewer arguments than expected? saved fp saved fp ret addr argi+2 argi+1 argi argi+2argi+1 argiret addr local 1local 2local 3local 4 low address high address

Calleeframe

Caller frame

fp sp Stack

Format String Vulnerabilities

printf()

ŷDzIf format includes format specifiers (subsequences beginning with %), the additional arguments following format are formatted and inserted in the resulting string replacing their respective specifiers.dz

ŷAlso, sprintf( char * str, constchar * format, ... );and fprintf( FILE * stream, constchar * format, ... );

ŷType and interpretation of the corresponding argument

ŷExamples:

ŷSign,ǡǡǥ

printf() ŷMinimum width of printed argument in characters (can be indirect)

ŷSizeofargument

ŷExamples:

Variadic Functions

ŷintprintf( constchar * format, ... );

called function know how many were passed in?

ŷAnother argument explicitly specifies count

ŷAnother argument implicitly encodes count

ŷThe last argument is a reserved terminator value

Format String Vulnerabilities

ŷprintfſũʩŪřbuf);

ŷprintf(buf);

in the format string. command interpreter.

Format String Vulnerabilities

ŷRead arbitrary memory

ŷWrite arbitrary memory

Format String Vulnerabilities: Reading

saved fp saved fp ret addr argi+2 argi+1 argi argi+2argi+1 argiret addr local 1local 2local 3local 4 low address high address

Calleeframe

Caller frame

fp sp Stack

Format String Vulnerabilities: Writing

ŷif (strlen(src) < sizeof(dst)) sprintf(dst, src);

ŷWhat if srccontains format specifiers?

sprintf( char * str, constchar * format, ... );

Format String Vulnerabilities: Writing

ŷ%n

ŷDzNothing printed. The corresponding argument must be a pointer to a signed int. The number of characters written so far is stored in the pointed location.dz printf("Hello %n ", &x); // after call x == 6 poses, this format specifier is disabled by default on many modern systems.

Format String Vulnerabilities: Writing

return address)

ŷHow to write a large 4-byte integer with %n?

size ŷMay work with printf(), but not with sprintf()

ŷWhy?

Format String Vulnerabilities: Writing

ŷxxxxxx12345678

ŷxxxxxx00000078

ŷxxxx00000056

ŷxx00000034

ŷ00000012

ŷxxxxxx12345678

ŷxxxxxx00000078

ŷxxxx00000156

ŷxx00000234

ŷ00000312

Format String Vulnerabilities: Writing

ŷ%hnwritesahalf-word

ŷ%hhnwrites a single byte

ŷNot universally supported

Avoiding Format String Vulnerabilities

of format specifiers: ŷ-Wformat: warn if format specifiers match arguments ŷ-Wformat-overflow: warn if destination might overflow ŷ-Wformat-security: warn if format string is not a string literal

ŷAnd manyothers

Additional Resources

Review

commandinterpreters.

Shellcode

Review: Smashing The Stack

ŷUpon function return, control is

transferred to an attacker-chosen address

ŷArbitrary code execution

code saved fp argi+2argi+1 argiret addr local 1local 2local 3local 4 low address high address fp sp Stack

Shellcode

pointer? process

ŷǡDzshellcodedz

Shellcode

with a new process image. The new image shall be constructed from a regular, executable file called the new process image file.dz

ŷexecveſũŵŵshŪřargv, NULL)

Shellcode

ŷWriting shellcode in C

review object code

ŷUsing a callinstruction to infer

the address of payload on the stack next word onto the stack as a return address void main() { char *name[2]; name[0] = "/bin/sh"; name[1] = NULL;quotesdbs_dbs4.pdfusesText_7
[PDF] format string vulnerability in c

[PDF] format string vulnerability solution

[PDF] format string vulnerability write to address

[PDF] formation a distance droit suisse

[PDF] formation adobe campaign

[PDF] formation apprendre à lire à deux

[PDF] formation après bts maintenance industrielle

[PDF] formation assurance qualité pharmaceutique et biotechnologique

[PDF] formation barreau en ligne gratuit

[PDF] formation bts maintenance industrielle afpa

[PDF] formation bts maintenance industrielle alternance

[PDF] formation bts maintenance industrielle greta

[PDF] formation cap petite enfance cours minerve

[PDF] formation maintenance industrielle ile de france

[PDF] formation naturopathe en ligne prix