I am seeing a steady trickle of scans for port 110 against my honeypot. Initially, I believed that the goal was brute forcing e-mail passwords. But instead, when setting up a quick netcat listener, I am seeing binary content without any obvious purpose. Various POP3 daemons have had vulnerabilities in the past, so maybe there is a way this is exploited? Or someone looking for backdoors that happen to listen on port 110 to disguise themselves. Can anybody help out with any ideas what this is about?

Here is a typical payload:

00000000  16 03 01 01 22 01 00 01  1e 03 03 a2 33 18 56 3f ...."... ....3.V?
00000010  b9 9a 05 1c 33 24 0c 83  03 bf 62 29 a6 37 22 da ....3$.. ..b).7".
00000020  33 e2 ac 9c 3c 44 28 bd  4d 8b d8 00 00 88 c0 30 3...<D(. M......0
00000030  c0 2c c0 28 c0 24 c0 14  c0 0a 00 a3 00 9f 00 6b .,.(.$.. .......k
00000040  00 6a 00 39 00 38 00 88  00 87 c0 32 c0 2e c0 2a .j.9.8.. ...2...*
00000050  c0 26 c0 0f c0 05 00 9d  00 3d 00 35 00 84 c0 12 .&...... .=.5....
00000060  c0 08 00 16 00 13 c0 0d  c0 03 00 0a c0 2f c0 2b ........ ...../.+
00000070  c0 27 c0 23 c0 13 c0 09  00 a2 00 9e 00 67 00 40 .'.#.... .....g.@
00000080  00 33 00 32 00 9a 00 99  00 45 00 44 c0 31 c0 2d .3.2.... .E.D.1.-
00000090  c0 29 c0 25 c0 0e c0 04  00 9c 00 3c 00 2f 00 96 .).%.... ...<./..
000000A0  00 41 c0 11 c0 07 c0 0c  c0 02 00 05 00 04 00 15 .A...... ........
000000B0  00 12 00 09 00 ff 01 00  00 6d 00 0b 00 04 03 00 ........ .m......
000000C0  01 02 00 0a 00 34 00 32  00 0e 00 0d 00 19 00 0b .....4.2 ........
000000D0  00 0c 00 18 00 09 00 0a  00 16 00 17 00 08 00 06 ........ ........
000000E0  00 07 00 14 00 15 00 04  00 05 00 12 00 13 00 01 ........ ........
000000F0  00 02 00 03 00 0f 00 10  00 11 00 23 00 00 00 0d ........ ...#....
00000100  00 20 00 1e 06 01 06 02  06 03 05 01 05 02 05 03 . ...... ........
00000110  04 01 04 02 04 03 03 01  03 02 03 03 02 01 02 02 ........ ........
00000120  02 03 00 0f 00 01 01                             .......

UPDATE

ok.. this was a bit too easy. After a bit of staring at the payload, it looked familiar. Turns out that this is an SSL Client hello (the 0x16 0x03 0x01 preamble gave it away). So now back to giving the attacker an SSL-enabled server to play with.

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Johannes B. Ullrich, Ph.D.
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