S3QL 1.18.1 and earlier uses the pickle Python module unsafely, which allows remote attackers to execute arbitrary code via a crafted serialized object in (1) common.py or (2) local.py in backends/.

S3QL before 2.27 mishandles checksumming, and consequently allows replay attacks in which an attacker who controls the backend can present old versions of the filesystem metadata database as up-to-date, temporarily inject zero-valued bytes into files, or temporarily hide parts of files. This is related to the checksum_basic_mapping function.