libxml2, possibly before 2.5.0, does not properly detect recursion during entity expansion, which allows context-dependent attackers to cause a denial of service (memory and CPU consumption) via a crafted XML document containing a large number of nested entity references, aka the "billion laughs attack."
Exploitability
AV:NAC:LPR:NUI:RScope
S:UImpact
C:NI:NA:H6.5/CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H