CVE-2021-31618
Publication date 15 June 2021
Last updated 25 August 2025
Ubuntu priority
Description
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.
Status
| Package | Ubuntu Release | Status |
|---|---|---|
| apache2 | 22.04 LTS jammy |
Not affected
|
| 20.04 LTS focal |
Not affected
|
|
| 18.04 LTS bionic |
Not affected
|
|
| 16.04 LTS xenial |
Not affected
|
|
| 14.04 LTS trusty |
Not affected
|
Notes
mdeslaur
per upstream advisory, "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." seems introduced by: https://github.com/apache/httpd/commit/a4fba223668c554e06bc78d6e3a88f33d4238ae4 Not sure the Debian patch in 2.4.46-5 is right, need to investigate
Patch details
| Package | Patch details |
|---|---|
| apache2 |
Severity score breakdown
| Parameter | Value |
|---|---|
| Base score |
7.5 · High
|
| Attack vector | Network |
| Attack complexity | Low |
| Privileges required | None |
| User interaction | None |
| Scope | Unchanged |
| Confidentiality | None |
| Integrity impact | None |
| Availability impact | High |
| Vector | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |