xmltok_impl.c in Expat (aka libexpat) before 2.4.5 lacks certain validation of encoding, such as checks for whether a UTF-8 character is valid in a certain context.
https://www.oracle.com/security-alerts/cpuapr2022.html
https://www.debian.org/security/2022/dsa-5085
https://security.netapp.com/advisory/ntap-20220303-0008/
https://security.gentoo.org/glsa/202209-24
https://lists.debian.org/debian-lts-announce/2022/03/msg00007.html
https://github.com/libexpat/libexpat/pull/562
https://cert-portal.siemens.com/productcert/pdf/ssa-484086.pdf