sot/source/sdstor/stgstrms.cxx in LibreOffice before 5.4.5.1 and 6.x before 6.0.1.1 uses an incorrect integer data type in the StgSmallStrm class, which allows remote attackers to cause a denial of service (use-after-free with write access) or possibly have unspecified other impact via a crafted document that uses the structured storage ole2 wrapper file format.
https://www.debian.org/security/2018/dsa-4178
https://usn.ubuntu.com/3883-1/
https://lists.debian.org/debian-lts-announce/2018/04/msg00021.html