Please have a look at firewalld version 0.4.4.1. This will be available in testing soon and should fix this issue.

firewalld-0.4.4.1-1.fc23 has been submitted as an update to Fedora 23. https://bodhi.fedoraproject.org/updates/FEDORA-2016-d2828a4793

firewalld-0.4.4.1-1.fc25 has been submitted as an update to Fedora 25. https://bodhi.fedoraproject.org/updates/FEDORA-2016-8d90406113

firewalld-0.4.4.1-1.fc24 has been submitted as an update to Fedora 24. https://bodhi.fedoraproject.org/updates/FEDORA-2016-c57b0ba2d4

firewalld-0.4.4.1-1.fc23 has been pushed to the Fedora 23 testing repository. If problems still persist, please make note of it in this bug report.
See https://fedoraproject.org/wiki/QA:Updates_Testing for
instructions on how to install test updates.
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2016-d2828a4793

firewalld-0.4.4.1-1.fc24 has been pushed to the Fedora 24 testing repository. If problems still persist, please make note of it in this bug report.
See https://fedoraproject.org/wiki/QA:Updates_Testing for
instructions on how to install test updates.
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2016-c57b0ba2d4

firewalld-0.4.4.1-1.fc25 has been pushed to the Fedora 25 testing repository. If problems still persist, please make note of it in this bug report.
See https://fedoraproject.org/wiki/QA:Updates_Testing for
instructions on how to install test updates.
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2016-8d90406113

firewalld-0.4.4.1-1.fc24 has been pushed to the Fedora 24 stable repository. If problems still persist, please make note of it in this bug report.

I'm sorry, but I installed firewalld-0.4.4.1-1.fc24 and it did not fix the bug. I still got the message "LCP: timeout sending Config-Requests" and connection is unsuccessful. Again, if the firewall is disabled, connection is successful.

Like Alexandre above, I installed firewalld-0.4.4.1-1.fc24 and it has not fixed this issue.
If net.netfilter.nf_conntrack_helper = 1 (see https://bugzilla.redhat.com/show_bug.cgi?id=1373014, which I raised), then making a VPN pptp connection works fine. However, if net.netfilter.nf_conntrack_helper = 0, then the connection times out.
This behaviour is exactly the same as the previous version of the firewall (which on Fedora24 was firewalld-0.4.3.3-1.fc24).
The update notes state that:
----
Automatic helper assignment has been disabled in kernel 4.7. firewalld version 0.4.4 is now able to recognize this and to create rules if automatic helper assignment has been turned off to make conntrack helpers work again.
-----
but that does not appear to be the case. If automatic helper assignment is turned off (that is, net.netfilter.nf_conntrack_helper = 0), then the VPN pptp connection fails.

firewalld 0.4.4 is providing support for net.netfilter.nf_conntrack_helper=0 within firewalld.

But if you connect to a VPN pptp server with NetworkManager, then NM is taking care about the connection and loads the pptp conntrack helper module. firewalld is not directly involved.

It seems that it is also needed to add support for the disabled automatic helper assignment in NetworkManager.

There is also a SELinux issue:

Please have a look at http://people.redhat.com/twoerner/firewalld/0.4.4.1-1/

There you can find an additional policy module definition file for SELinux: firewalld-0.4.4.te

It only allows firewalld to search and analyse if there are usable netfilter conntrack helpers:

allow firewalld_t modules_object_t:dir { getattr open search read };

Please have a look at the file SELINUX.README to be able to enable and use the module.

Re Comment 11 about NetworkManger.

Thanks Thomas, I didn't realize that NM was dealing with the connection without involving firewalld.
There's already an outstanding bug (https://bugzilla.redhat.com/show_bug.cgi?id=1375006) on NM-pptp, so I'll add a comment there. Unfortunately, that bug seems to have been open for 2 months with no input from the assignee :-(

Anyway, thanks for your work on firewalld!

Thomas, thanks for your help. Seems that the change in conntrack helper default setting is the cause of a lot of bugs here!

firewalld-0.4.4.2-1.fc25 has been submitted as an update to Fedora 25. https://bodhi.fedoraproject.org/updates/FEDORA-2016-3dd8b5f4e1

firewalld-0.4.4.2-1.fc23 has been submitted as an update to Fedora 23. https://bodhi.fedoraproject.org/updates/FEDORA-2016-b566ecf579

firewalld-0.4.4.2-1.fc23 has been pushed to the Fedora 23 testing repository. If problems still persist, please make note of it in this bug report.
See https://fedoraproject.org/wiki/QA:Updates_Testing for
instructions on how to install test updates.
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2016-b566ecf579

firewalld-0.4.4.2-1.fc25 has been pushed to the Fedora 25 testing repository. If problems still persist, please make note of it in this bug report.
See https://fedoraproject.org/wiki/QA:Updates_Testing for
instructions on how to install test updates.
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2016-3dd8b5f4e1

firewalld-0.4.4.2-1.fc25 has been pushed to the Fedora 25 stable repository. If problems still persist, please make note of it in this bug report.

firewalld-0.4.4.2-2.fc23 selinux-policy-3.13.1-158.25.fc23 has been submitted as an update to Fedora 23. https://bodhi.fedoraproject.org/updates/FEDORA-2016-8a0533d057

firewalld-0.4.4.2-2.fc23, selinux-policy-3.13.1-158.25.fc23 has been pushed to the Fedora 23 testing repository. If problems still persist, please make note of it in this bug report.
See https://fedoraproject.org/wiki/QA:Updates_Testing for
instructions on how to install test updates.
You can provide feedback for this update here: https://bodhi.fedoraproject.org/updates/FEDORA-2016-8a0533d057

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