It was found that systemd fails an assertion in managerinvokenotifymessage() 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 managerinvokenotifymessage(), or have managerprocessnotifyfd() function return error before calling managerinvokenotifymessage(). 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 managerinvokenotifymessage() 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 managerinvokenotifymessage() 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.