CVE-2026-59646: DTLS handshake reassembler allocates buffer from unchecked 24-bit length

Affects Bouncy Castle for Java FIPS (BC-FJA) bctls-fips before 1.0.24 (1.0.X series), 2.0.24 (2.0.X series) and 2.1.24 (2.1.X series). DTLSReliableHandshake.processRecord() allocates a reassembly buffer sized from the 24-bit handshake length field of an incoming record, without the maximum-message-size check the stream-TLS path applies. Up to sixteen message sequences may be buffered per connection, so a single record of about 205 bytes carrying sixteen fragment headers with a maximal length forces roughly 256 MiB of allocation before any authentication. A few small UDP datagrams can drive the JVM to OutOfMemoryError.