Message Authentication in WEP

An 802.11 receiver will accept a packet if, after decryption, the last four bytes of the plaintext form a correct checksum on the remainder of the plaintext.
This remainder will be the message accepted.
The checksum algorithm used is CRC-32
This is quite a poor choice
CRC's are used to detect random errors; they are useless against malicious errors.
There is already a CRC at a lower layer of the protocol to detect random bit errors in transmission.
CRC-32 has two main properties of importance here:
It is independent of the shared secret and the IV
It is linear: c(M XOR D) = c(M) XOR c(D)