Early versions of amphp/http-client with HTTP/2 support (v4.0.0-rc10 to 4.0.0) will collect HTTP/2 CONTINUATION frames in an unbounded buffer and will not check the header size limit until it has received the END_HEADERS flag, resulting in an OOM crash. Later versions of amphp/http-client (v4.1.0-rc1 and up) depend on amphp/http for HTTP/2 processing and will therefore need an updated version of amphp/http, see GHSA-qjfw-cvjf-f4fm.