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.
http://httpd.apache.org/security/vulnerabilities_24.html
https://seclists.org/oss-sec/2021/q2/206
https://lists.apache.org/thread.html/[email protected]%3Ccvs.httpd.apache.org%3E
https://lists.apache.org/thread.html/[email protected]%3Ccvs.httpd.apache.org%3E
http://www.openwall.com/lists/oss-security/2021/06/10/9
https://lists.debian.org/debian-lts-announce/2021/07/msg00006.html
https://www.debian.org/security/2021/dsa-4937
https://security.gentoo.org/glsa/202107-38
Source: MITRE
Published: 2021-06-15
Updated: 2021-12-10
Type: CWE-476
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