In libexpat before 2.8.2, there is a heap-based buffer overflow in doProlog in xmlparse.c because scaffold backing array reallocation is mishandled when there is data-structure sharing across parsers.
Exploitability
AV:LAC:HPR:NUI:NScope
S:UImpact
C:HI:HA:L6.9/CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:LOther