Apache httpd before version 2.4.34 has a vulnerability in mod_md. By specially crafting HTTP requests, the mod_md challenge handler would dereference a NULL pointer and cause the child process to segfault. This could be used to DoS the server.
The affected mod_md module was only introduced upstream in version 2.4.30 as an experimental module:
*) mod_md: new experimental, module for managing domains across virtual hosts,
implementing the Let's Encrypt ACMEv1 protocol to signup and renew
certificates. Please read the modules documentation for further instructions
on how to use it. [Stefan Eissing]
Note that versions 2.4.30 and 2.4.31 were not released, so the first released version with this functionality was 2.4.32.
Created httpd tracking bugs for this issue:
Affects: fedora-all [bug 1605093]
This should be the patch, as applied to the mod_md git repo:
It notes the following fix for the mod_md 1.1.11:
* fixes a Null Dereference when specially crafted requests are sent to the
server. Reported by Daniel Caminada <email@example.com>.
However, that commit includes additional unrelated changes (from mod_md 1.1.12). The relevant part should be the second and the third change to the mod_md.c file.
The fix integrated to httpd trunk via this commit:
The fix to the 2.4 branch was even combined with lot of other changes, updating mod_md from version 1.0.8 to 1.1.15:
Created attachment 1464893 [details]
mod_md CVE-2018-8011 patch
According to (previously private) discussion at firstname.lastname@example.org, the specific fix for the mod_md issue is as attached. I am making it public here for full disclosure.