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.
https://www.cisa.gov/news-events/ics-advisories/icsa-24-319-04
https://nowotarski.info/http2-continuation-flood/
https://kb.cert.org/vuls/id/421644
https://www.openwall.com/lists/oss-security/2024/04/03/16
https://support.apple.com/kb/HT214119
https://httpd.apache.org/security/vulnerabilities_24.html