crypto AuthencESN Corruption

Vulnerability analysis

The vulnerability stems from incorrect handling of high-order sequence number bits during out-of-place decryption (src != dst) in the authencesn AEAD implementation. The original code performed scatterlist operations on the destination buffer assuming an in-place layout, resulting in a 4-byte out-of-bounds read from beyond the destination buffer and a 4-byte out-of-bounds write past the end of the destination buffer. This occurs before the authentication check, meaning the corruption is triggered regardless of whether the ciphertext is valid. The fix separates in-place and out-of-place decryption logic, ensuring sequence number bits are correctly rearranged without accessing memory outside the destination buffer bounds.