A highly critical vulnerability in the OpenSSL library which allows an attacker to obtain random 64kByte blocks of memory from the process using said library, which could include user credentials, private SSL keys, and other data sent/received from the server.
OpenSSL Security Advisory [07 Apr 2014]
TLS heartbeat read overrun (CVE-2014-0160)
A missing bounds check in the handling of the TLS heartbeat extension can be used to reveal up to 64k of memory to a connected client or server.
Only 1.0.1 and 1.0.2-beta releases of OpenSSL are affected including 1.0.1f and 1.0.2-beta1.
Thanks for Neel Mehta of Google Security for discovering this bug and to Adam Langley and Bodo Moeller for preparing the fix.
Affected users should upgrade to OpenSSL 1.0.1g. Users unable to immediately upgrade can alternatively recompile OpenSSL with -DOPENSSL_NO_HEARTBEATS.
1.0.2 will be fixed in 1.0.2-beta2.