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 issue affected mod_http2 1.15.17 and Apache HTTP Server version 2.4.47 only. Apache HTTP Server 2.4.47 was never released.

References[email protected][email protected][email protected]/message/A73QJ4HPUMU26I6EULG6SCK67TUEXZYR/[email protected]/message/2NKJ3ZA3FTSZ2QBBPKS6BYGAWYRABNQQ/


Source: MITRE

Published: 2021-06-15

Updated: 2021-12-10

Type: CWE-476

Risk Information


Base Score: 5

Vector: AV:N/AC:L/Au:N/C:N/I:N/A:P

Impact Score: 2.9

Exploitability Score: 10

Severity: MEDIUM


Base Score: 7.5

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Impact Score: 3.6

Exploitability Score: 3.9

Severity: HIGH