TypeError: can't concat str to bytes

[zmw12306]

Configuration

impacket version: Impacket v0.12.0
Python version: Python 3.10.12
Target OS: Linux ubuntu

Debug Output With Command String

Raw IP packet: b'o\x05\x05\x05\x05\x05\x05\x05\x05\x01\x05s\x05\x05\x05\x05q\x03\x05\x05\x05\x05p\x01\x05\x05'
Traceback (most recent call last):
File "/home/youwei/XDiff/Impacket/IP.py", line 22, in
ip_packet = decoder.decode(Ip_packet)
File "/home/youwei/.local/share/pipx/venvs/impacket/lib/python3.10/site-packages/impacket/ImpactDecoder.py", line 191, in decode
ip6_packet = IP6.IP6(buffer)
File "/home/youwei/.local/share/pipx/venvs/impacket/lib/python3.10/site-packages/impacket/IP6.py", line 32, in init
self.load_header(buffer)
File "/home/youwei/.local/share/pipx/venvs/impacket/lib/python3.10/site-packages/impacket/ImpactPacket.py", line 435, in load_header
aBuffer += '\x00'
TypeError: can't concat str to bytes

### PCAP  
Raw IP packet: b'o\x05\x05\x05\x05\x05\x05\x05\x05\x01\x05s\x05\x05\x05\x05q\x03\x05\x05\x05\x05p\x01\x05\x05'

[alexisbalbachan]

Hi, could you provide some context on how you got that raw ip packet?
IPv6 headers should have a fixed size of 40 bytes while that packet is 26 bytes.

[zmw12306]

The code is designed to handle cases where the packet length (packetlen) does not match the expected fixed size (hdr_len). When the provided aBuffer is shorter than hdr_len, the code attempts to pad aBuffer with additional bytes by appending '\x00'. This padding is meant as an error handling step to ensure aBuffer reaches the required length. However, this approach is causing a crash because aBuffer is a byte string, and appending '\x00' (a regular string) results in a TypeError, as you can't concatenate a string to a byte object.

To fix this, we need to change '\x00' to b'\x00' so that aBuffer is padded with bytes instead of a regular string. Here's how the modified code would look:

if len(aBuffer) < hdr_len:
    diff = hdr_len - len(aBuffer)
    for _ in range(diff):
        aBuffer += b'\x00'

[alexisbalbachan]

Nice catch! I'm creating a PR with this fix.