China GFW blocking shadowsocks (other ports/services work)

[pjrobertson]

What version of shadowsocks-libev are you using?

Server: shadowsocks-libev 3.2.3
Client: shadowsocks-libev 3.2.3 / Shadowsocks-NG 1.8.2

What operating system are you using?

Server: Ubuntu 16.04
Client: CentOS / MacOS 10.14.2

What did you do?

Been using the server as a shadowsocks proxy for 1-2 years no problem (set up using streisand and default settings). As of last week the shadowsocks connections are being blocked. I tried re-installing shadowsocks-libev from scratch (by re-running streisand) and making sure I'm using the latest ciphers, yet still not working. Since the server was set up 2 years ago, the Encryption type was aes-256-cfb (I know this was kind of old - may be an explanation as to how the GFW managed to block the server)

Also tried installing simple-obfs on the server/client and using that.

What did you expect to see?

A working shadowsocks from within China.

What did you see instead?

All shadowsocks connections are being blocked when trying to connect from a China based IP. Tried multiple encryptions (aes-256-cfb and chacha20-ietf-poly1305), also different ports (8530 and 8540).
Connecting from servers outside of China works no problem.

HTTPS / SSH are all open, so the server IP itself isn't being blocked, just the Shadowsocks protocol. simple-obfs with http is also being blocked.

What is your config in detail (with all sensitive info masked)?

{
    "server":"A.B.C.D",
    "server_port":8530,
    "local_port":1080,
    "password":"pass",
    "timeout":600,
    "method":"chacha20-ietf-poly1305",
    "fast_open":false,
    "plugin":"obfs-server",
    "plugin_opts":"obfs=http"
}

I'm happy to provide the server details, so that others can debug. To me this looks like a GFW getting smarter at determining what is a shadowsocks connection, and what isn't.

[madeye]

1. Try FTP/HTTP/HTTPS ports.
2. simple-obfs is already deprecated. Try https://github.com/shadowsocks/v2ray-plugin and https://github.com/shadowsocks/kcptun
3. Recent blocking has nothing to do with protocols, any suspicious ports and traffic from popular VPS providers are all blocked.

[pjrobertson]

Double checked, and turns out it was a simple IP + port block. When I previously tried changing ports I'd forgotten to open up the new port in the firewall. After opening the port things worked.

I guess the question here is: how did the GFW know to block that port? Was it a simple hard-coded rule "port 8530 is a common shadowsocks port, so block it" or what there something cleverer? I'll see if the new port gets blocked.

Thanks for the quick response @madeye , and for all the work you're doing on this project :)

[madeye]

Fully encrypted traffic with very high entropy is obviously suspicious. Please refer to https://github.com/isofew/sssniff for more details.

[zzws524]

I encoutered same issue. I have exact same settings for 2 different ports. After one port was blocked, I switched to the other one. It's working without changing anything on the server side.

The config json file like this:
...
"port_password":{
"9003":"passport1",
"9002":"passport2"
},
...
So I decided to alway keep two unblocked port in use.

The encryptions I used was an old one (aes-192-cfb). I am not sure if I choose a newer encryption, GFW would take longer time to detect my ss.

[desmax]

already experienced this 2 times. it just blocks my port.
my encryption is aes-256-cfb

[pjrobertson]

I no longer have any issues with the GFW. Try disabling any plugins (obfs). Here's my config:

{
    "server":"A.B.C.D",
    "server_port":8530,
    "local_port":1080,
    "password":"abc",
    "timeout":600,
    "method":"chacha20-ietf-poly1305",
    "fast_open":false,
}

[metalbreeze]

What i met is different:
June 10, my (only Encrytion chacha,no Obfs &no Protocal.) + my friends ss , those ips were blocked suddenly . I guess there was a gfw upgrade.

After sniffed suspect traffic , GFW do a detect , after “somehow” confirm, all traffice start to block ,even ping.
GFW will also do more detects in few mins, if no suspected port(i reboot the vm) , the traffice will be normal.

(a detect, because i just setup a SS on a vm with a new ip at a port,no one knows before)

(start to block, after SS stopped , all traffic will be normal)

After using AES-256-cfb simple_http auth_sha1_v4 , it seemed there are still incoming detects, but gfw can not desiced if it is ss or not. So, won't block anymore.

[eldoonreval]

What i met is different:
June 10, my (only Encrytion chacha,no Obfs &no Protocal.) + my friends ss , those ips were blocked suddenly . I guess there was a gfw upgrade.

After sniffed suspect traffic , GFW do a detect , after “somehow” confirm, all traffice start to block ,even ping.
GFW will also do more detects in few mins, if no suspected port(i reboot the vm) , the traffice will be normal.

(a detect, because i just setup a SS on a vm with a new ip at a port,no one knows before)

(start to block, after SS stopped , all traffic will be normal)

After using AES-256-cfb simple_http auth_sha1_v4 , it seemed there are still incoming detects, but gfw can not desiced if it is ss or not. So, won't block anymore.

thanks for the information. will change it to aes-256-cfb to see if more IPs will be blocked!

[OrangeKnife]

Same here
At first, ports are banned ( I changed a few times)
then Ip is banned
Fuck it.

[shubhvachher]

Same as @OrangeKnife... First port ban and if you just change ports multiple time (4 times for me I think), you get an IP ban. Warning, for whoever comes across this thread.

@metalbreeze , could you please clarify on what you mean by

...using AES-256-cfb simple_http auth_sha1_v4...

Do you mean AES-256-cfb with a simple http obfs using plugin (obfuscating)? What do you mean by use auth_sha1_v4 then?

[niuzb]

any update, my SS also been blocked today, after changing the port, still been blocked after a while

[nadimaj]

And there goes my last life line. The barstewards first increasingly made it unreliable but today it's totally gone. ShadowSocks is not bulletproof like I thought. If your server is hosted with a popular hosting company, only a matter of time until they work out what's going on.