HTTP/2 incoming headers exceeding the limit are temporarily buffered in nghttp2 in order to generate an informative HTTP 413 response. If a client does not stop sending headers, this leads to memory exhaustion.
Exploitability
AV:NAC:LPR:NUI:NScope
S:UImpact
C:NI:NA:H7.5/CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:HResource Management