Apache HTTP Server: modhttp2 denial of service

Late Release of Memory after Effective Lifetime vulnerability in Apache HTTP Server.

This issue affects Apache HTTP Server: from 2.4.17 up to 2.4.63.

Users are recommended to upgrade to version 2.4.64, which fixes the issue.

Accounts. The issue was addressed with improved checks.

Apache HTTP Server, with MPM event, worker or prefork, code executing in less-privileged child processes or threads (including scripts executed by an in-process scripting interpreter) could execute code with the privileges of the parent process (usually root) by manipulating the scoreboard.

In Apache httpd 2.0.23 to 2.0.65, 2.2.0 to 2.2.34, and 2.4.0 to 2.4.29, modauthnzldap, if configured with AuthLDAPCharsetConfig, uses the Accept-Language header value to lookup the right charset encoding when verifying the user's credentials. If the header value is not present in the charset conversion table, a fallback mechanism is used to truncate it to a two characters value to allow a quick retry (for example, 'en-US' is truncated to 'en'). A header value of less than two characters forces an out of bound write of one NUL byte to a memory location that is not part of the string. In the worst case, quite unlikely, the process would crash which could be used as a Denial of Service attack. In the more likely case, this memory is already reserved for future use and the issue has no effect at all.

A crafted method sent through HTTP/2 will bypass validation and be forwarded by modproxy, which can lead to request splitting or cache poisoning. This issue affects Apache HTTP Server 2.4.17 to 2.4.48.

A use-after free vulnerability was found in apache httpd. There's an apache configuration directive <Limit> that can be used to restrict access to certain HTTP methods. If one sets this inside an .htaccess file with an HTTP method that's not registered in the server the bug happens (e.g. set <Limit INVALID></Limit> in .htaccess). The reason is that at that point the variables used to build up the "Allow" header have already been freed, as it's not expecting any more changes to it.

Note that the bug only appears with OPTIONS requests to a specific path, not with "" OPTIONS requests.

An attacker on a shared hosting could could deliberately create an .htaccess file triggering the bug and subsequently try to exfiltrate data pieces from the global apache process that may contain secrets like password hashes.

Upstream patch:

https://svn.apache.org/viewvc?view=revision&revision=1807754

apache. Multiple issues existed in Apache. These were addressed by updating Apache to version 2.4.25.