In June I started playing with fingerprinting SSL client requests. For example, an SSL fingerprint of my browser is:
I wanted to prepare a database of popular fingerprints, so I started recording traffic on port 443.
I quickly noticed that apart from normal traffic there are some hosts sending weird SSL requests that make no practical sense and look like scanning. It's not really surprising, for example it is well known that EFF SSL Observatory did an active SSL scan.
# Probing SSL 2.0 2.0:700c0,30080,10080,60040,40080,20080::v2,chlen 3.1:15,ff::v2 # Ciphers enumerating 3.1:9:ff01: 3.1:15:ff01: # Some probes don't have random data where necessary 3.0:0::rand 3.2:1f::rand 3.3:c002:b,d:rand # 0xff is not really a valid cipher 3.3:ff:b,d:rand # Ordering of ciphers 3.3:4,5,9,a,15,16,2f,33,35,39:b,d:rand 3.3:5,9,a,15,16,2f,33,35,39,4:b,d:rand # Repeated cipher 0x80 3.0:80,80,40,c0,9,a,15,16,2f,33,35,39,80,80,4,5::rand
Requests from SSL Labs were pretty weird, but at least thet serve a
legitimate purpose - www.ssllabs.com
provides a very useful service. But the clear winner in number of
126.96.36.199 belonging to "Netco
Solutions Ltd" form Norfolk which generated a record number of 862
As opposed to SSL Labs I have no clue what their scans were for.
# SSL 2.0 probe 2.0:700c0,50080,30080,10080,80080,60040,40080,20080::v2,chlen # Support for compression 3.3:2a,31,66,b,c,c038,3c,...,2b,25,29,1f,2,c001,23:: 3.3:2a,31,66,b,c,c038,3c,...,2b,25,29,1f,2,c001,23::compr # Random timestamp field 3.0:16,13,a,66,5,4,65,64,63,62,61,60,15,12,9,14,11,8,6,3::rtime
Johns Hopkins University
I recorded two nearly identical scans: one from Johns Hopkins University
188.8.131.52 and another from a random Amazon
184.108.40.206. They were composed of
91 signatures, mostly just enumerating ciphers.
I don't think there's anything special about those scans, maybe the fact that they seem to be really detailed about SSL v2:
2.0:10080::v2,chlen 2.0:20080::v2,chlen 2.0:30080::v2,chlen 2.0:40080::v2,chlen 2.0:60040::v2,chlen 2.0:700c0::v2,chlen 2.0:700c0,30080,10080,60040,40080,20080::v2,chlen
(Prof. Matthew Green from Johns Hopkins University might know more about the nature of the scan.)
Another interesting scan came from Amazon UE-EAST
220.127.116.11. This looks somewhat similar to
scans from Johns Hopkins University, but it's hard to judge if they
are related. Also, this scan was much larger with 344 unique probes.
Except from the usual SSL v2 scanning it had some quite weird probes.
# SSL v2 testing, with non-random data in challenge field 2.0:ff,10080,30080,700c0,60040,20080,40080::v2,rand 3.1:ff,35,2f,a,4,5,10080,30080,700c0,60040,20080,40080::v2,rand # Two probes: a valid and a random timestamp 3.2:ff,35,2f,a,4,5::ver 3.2:ff,35,2f,a,4,5::ver,rtime # Checking ciphers, in order? 3.0:1,2,b,e,11,7,c,f,12,d,10,36,37,3e,3f,68,69,13,38,[...] [...],bf,c0,c1,c2,c3,c4,c5,80,81,82,83:?0,ff01,5,23:rtime # Is that a probe for TLS 1.3? 3.4:3d,3c,35,2f,a,4,5:?0,ff01,5,23,d:ver,rtime 3.4:ff,3d,3c,35,2f,a,4,5::ver,rtime # What exactly is protocol 4.1? 4.1:3d,3c,35,2f,a,4,5:?0,ff01,5,23,d:ver,rtime 4.1:ff,3d,3c,35,2f,a,4,5::ver,rtime
Checking the support of non-existent versions of SSL is definitely my favourite scan.
Actually, it's does serve a purpose - TLS spec vaguely defines how to do TLS version negotiation but I don't think it's widely supported. Most browsers just try a best TLS version first (TLS 1.2 nowadays) and fall back to older TLS 1.1 if server returns an error.
Requesting an impossible version of TLS may be used to detect how servers behave in the fallback situation. Still, testing protocol 4.1 is quite suspicious.
It's also worth noting - the Opera browser has a custom SSL stack, different from any other browser. Maybe those scans check if Opera will actually work with real SSL servers.
Although I didn't receive an SSL scan generated by Nmap, I thought it would be useful to mention it.
For some time Nmap includes a scripting engine and one of the scripts is capable of enumerating SSL ciphers `ssl-enum-ciphers'. To run it:
nmap -p443 --script scripts/ssl-enum-ciphers.nse host
For my server it generates this report:
PORT STATE SERVICE 443/tcp open https | ssl-enum-ciphers: | SSLv3: | ciphers: | TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA - strong | TLS_DHE_RSA_WITH_AES_128_CBC_SHA - strong | TLS_DHE_RSA_WITH_AES_256_CBC_SHA - strong | TLS_DHE_RSA_WITH_DES_CBC_SHA - weak | TLS_RSA_WITH_3DES_EDE_CBC_SHA - strong | TLS_RSA_WITH_AES_128_CBC_SHA - strong | TLS_RSA_WITH_AES_256_CBC_SHA - strong | TLS_RSA_WITH_DES_CBC_SHA - weak | TLS_RSA_WITH_RC4_128_MD5 - strong | TLS_RSA_WITH_RC4_128_SHA - strong | compressors: | NULL | TLSv1.0: | ciphers: | TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA - strong | TLS_DHE_RSA_WITH_AES_128_CBC_SHA - strong | TLS_DHE_RSA_WITH_AES_256_CBC_SHA - strong | TLS_DHE_RSA_WITH_DES_CBC_SHA - weak | TLS_RSA_WITH_3DES_EDE_CBC_SHA - strong | TLS_RSA_WITH_AES_128_CBC_SHA - strong | TLS_RSA_WITH_AES_256_CBC_SHA - strong | TLS_RSA_WITH_DES_CBC_SHA - weak | TLS_RSA_WITH_RC4_128_MD5 - strong | TLS_RSA_WITH_RC4_128_SHA - strong | compressors: | NULL
On the server it generates 71 signatures (for my particular setup), looking like this.
Things like EFF Observatory and SSL Labs prove SSL scanning may be used for legitimate purposes, but much more scanning is happening in the wild. I'm not sure it it's good or bad, but I fear that there isn't enough visibility generated by the SSL servers. SSL errors seem not to be logged and servers don't notice they are being scanned.
I think there is much more to SSL scanning, I feel this article barely scratches the surface.