![]() ![]() note: this does not include the padding bytes The diagram below shows how the attack works:Ĭlick to enlarge. Whoever sends a HeartbeatMessage controls the payload_length but as we will see, this is never checked against the parent SS元_RECORD's length field, allowing an attacker to overrun memory. Meanwhile, inside the received HeartbeatMessage, payload_length is the number of bytes in the arbitrary payload that has to be sent back. So just to be clear, the SS元 record's data points to the start of the received HeartbeatMessage and length is the number of bytes in the received HeartbeatMessage. Unsigned char *data /* pointer to the record data */ Unsigned int length /* How many bytes available */ The key fields in SS元_RECORD are given below length is how many bytes are in the received HeartbeatMessage and data is a pointer to that HeartbeatMessage. This HeartbeatMessage arrives via an SS元_RECORD structure, a basic building block of SSL/TLS communications. The heartbeat message, according to the official standard, looks like this, in C: The bug lies in OpenSSL's implementation of the TLS heartbeat extension: it's a keep-alive feature in which one end of the connection sends a payload of arbitrary data to the other end, which sends back an exact copy of that data to prove everything's OK. The patch is here, and the blunder is far worse than Apple's gotofail. An attacker can trick OpenSSL into allocating a 64KB buffer, copy more bytes than is necessary into the buffer, send that buffer back, and thus leak the contents of the victim's memory, 64KB at a time. This serious flaw ( CVE-2014-0160) is a missing bounds check before a memcpy() call that uses non-sanitized user input as the length parameter. ![]()
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