A vulnerability in OpenSSL versions from 0.9.24 up to but not including 0.10.78 allows unchecked callback lengths in PSK and cookie callbacks. Callbacks that return a length larger than their buffer cause OpenSSL to read beyond the buffer's end. For cookie callbacks, this can lead to disclosure of adjacent memory over the network. The issue is fixed in version 0.10.78 by validating the returned length against the buffer size and treating excessive lengths as callback failures.