Quoting form the OpenSSL upstream advisory:
Fix Use After Free for large message sizes (CVE-2016-6309)
This issue only affects OpenSSL 1.1.0a, released on 22nd September 2016.
The patch applied to address CVE-2016-6307 resulted in an issue where if a
message larger than approx 16k is received then the underlying buffer to store
the incoming message is reallocated and moved. Unfortunately a dangling pointer
to the old location is left which results in an attempt to write to the
previously freed location. This is likely to result in a crash, however it
could potentially lead to execution of arbitrary code.
OpenSSL 1.1.0 users should upgrade to 1.1.0b
This issue was reported to OpenSSL on 23rd September 2016 by Robert
Święcki (Google Security Team), and was found using honggfuzz. The fix
was developed by Matt Caswell of the OpenSSL development team.
The CVE-2016-6307 is tracked via bug 1378203.
The following commit seems to add test for this issue into upstream test suite:
This issue did not affect any Red Hat product as they do not yet include OpenSSL 1.1.0.