Problem: NEWS does not mention security advisories

Solution: add them

Author: bluca

NEWS

@@ -1,6 +1,44 @@
 0MQ version 4.3.x stable, released on 20xx/xx/xx
 ================================================
 
+* Security advisories:
+  * CVE-2020-15166: Denial-of-Service on CURVE/ZAP-protected servers by
+    unauthenticated clients.
+    If a raw TCP socket is opened and connected to an endpoint that is fully
+    configured with CURVE/ZAP, legitimate clients will not be able to exchange
+    any message. Handshakes complete successfully, and messages are delivered to
+    the library, but the server application never receives them.
+    For more information see the security advisory:
+    https://github.com/zeromq/libzmq/security/advisories/GHSA-25wp-cf8g-938m
+  * Stack overflow on server running PUB/XPUB socket (CURVE disabled).
+    The PUB/XPUB subscription store (mtrie) is traversed using recursive
+    function calls. In the remove (unsubscription) case, the recursive calls are
+    NOT tail calls, so even with optimizations the stack grows linearly with the
+    length of a subscription topic. Topics are under the control of remote
+    clients - they can send a subscription to arbitrary length topics. An
+    attacker can thus cause a server to create an mtrie sufficiently large such
+    that, when unsubscribing, traversal will cause a stack overflow.
+    For more information see the security advisory:
+    https://github.com/zeromq/libzmq/security/advisories/GHSA-qq65-x72m-9wr8
+  * Memory leak in PUB server induced by malicious client(s) without CURVE/ZAP.
+    Messages with metadata are never processed by PUB sockets, but the metadata
+    is kept referenced in the PUB object and never freed.
+    For more information see the security advisory:
+    https://github.com/zeromq/libzmq/security/advisories/GHSA-4p5v-h92w-6wxw
+  * Memory leak in client induced by malicious server(s) without CURVE/ZAP.
+    When a pipe processes a delimiter and is already not in active state but
+    still has an unfinished message, the message is leaked.
+    For more information see the security advisory:
+    https://github.com/zeromq/libzmq/security/advisories/GHSA-wfr2-29gj-5w87
+  * Heap overflow when receiving malformed ZMTP v1 packets (CURVE disabled).
+    By crafting a packet which is not valid ZMTP v2/v3, and which has two
+    messages larger than 8192 bytes, the decoder can be tricked into changing
+    the recorded size of the 8192 bytes static buffer, which then gets overflown
+    by the next message. The content that gets written in the overflown memory
+    is entirely decided by the sender.
+    For more information see the security advisory:
+    https://github.com/zeromq/libzmq/security/advisories/GHSA-fc3w-qxf5-7hp6
+
 * Note for packagers: an external, self-contained sha1 library is now
   included in the source tree under external/sha1/ - it is licensed
   under BSD-3-Clause and thus it is fully compatible with libzmq's