libexpat before 2.7.5 allows a NULL pointer dereference with empty external parameter entity content.
https://www.cisa.gov/news-events/ics-advisories/icsa-26-155-04
https://github.com/libexpat/libexpat/pull/1159
https://github.com/libexpat/libexpat/pull/1158
https://cert-portal.siemens.com/productcert/html/ssa-082556.html