In rsync 3.0.1 through 3.4.1, receive_xattr relies on an untrusted length value during a qsort call, leading to a receiver use-after-free. The victim must run rsync with -X (aka --xattrs). On Linux, many (but not all) common configurations are vulnerable. Non-Linux platforms are more widely vulnerable.
Rsync: Out of bounds array access via negative index
A malicious client acting as the receiver of an rsync file transfer can trigger an out of bounds read of a heap based buffer, via a negative array index. The
malicious
rsync client requires at least read access to the remote rsync module in order to trigger the issue.