CVE-2021-31618: NULL pointer dereference on specially crafted HTTP/2 request

Severity: important

Vendor: The Apache Software Foundation

Versions Affected:
Apache HTTP Server 2.4.47
Apache HTTP Server protocol handler for the HTTP/2 protocol checks received 
request headers against the size limitations as configured for the server and 
used for the HTTP/1 protocol as well. On violation of these restrictions and 
HTTP response is sent to the client with a status code indicating why the 
request was rejected.

This rejection response was not fully initialised in the HTTP/2 protocol 
handler if the offending header was the very first one received or appeared in 
a a footer. This led to a NULL pointer dereference on initialised memory, 
crashing reliably the child process. Since such a triggering HTTP/2 request is 
easy to craft and submit, this can be exploited to DoS the server.

This affected versions prior to 2.4.47


Apache HTTP server would like to thank  LI ZHI XIN from NSFocus for reporting 


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