It was found that systemd fails an assertion in manager_invoke_notify_message() when a zero-length message is received over its notification socket, causing it to no longer perform it's expected functionality.  This issue was assigned CVE-2016-7795 and is tracked via bug 1380286.  Upstream bug report is:

https://github.com/systemd/systemd/issues/4234

Older systemd versions either don't include the assert that is triggered in manager_invoke_notify_message(), or have manager_process_notify_fd() function return error before calling manager_invoke_notify_message().  That error return still causes systemd to exit its main loop and freeze its execution in a similar way it's done in newer versions after failed assertion.

https://github.com/systemd/systemd/issues/4234#issuecomment-250441246

The manager_invoke_notify_message() function with assert was introduced in version v209:

https://github.com/systemd/systemd/commit/5ba6985b6c8ef85a8bcfeb1b65239c863436e75b#diff-ab78220e12703ee63fa1e6a2caa16bebR1319

However, the assertion was not reachable before the error return was removed in v219:

https://github.com/systemd/systemd/commit/d875aa8ce10b458dc218c0d98f4a82c8904d6d03

The systemd versions in Red Hat Enterprise Linux 7.0 and 7.1 are based on upstream v208, but include manager_invoke_notify_message() added via a separate backported patch.  The assertion is not reachable, so those versions are affected by CVE-2016-7796, but not affected by CVE-2016-7795.  Red Hat Enterprise Linux 7.2 rebased systemd to version v219.  Therefore, those packages are no longer affected by CVE-2016-7796, but are now affected by CVE-2016-7795.