lz4-sys up to v1.9.3 bundles a version of liblz4 that is vulnerable to CVE-2021-3520.
Attackers could craft a payload that triggers an integer overflow upon decompression, causing an out-of-bounds write.
The flaw has been corrected in version v1.9.4 of liblz4, which is included in lz4-sys 1.9.4.