How to enable TLS 1.1 **minimum** on vsftpd

Question

I'm trying to secure my infrastructure to meet the PCI-DSS standard using securitymetrics.com. The standard mandates the use of TLS 1.1 minimum (with a CBC cipher). TLS 1.0 is not allowed.

While securing ftp (vsftpd), I have disabled sslv2 and sslv3, but couldn't block TLS 1.0 without also disabling TLS 1.1 and TLS 1.2. The config file has the ssl_tlsv1 option that can be set to YES or NO, but I don't see any way to distinguish between 1.0 and later versions.

How can I enable only TLS 1.1 and better?

Answer 1

Answer isn't posted, so I thought I'd follow up for the rest...

To disable TLSv1.0 and enable TLSv1.1 and TLSv1.2 just add these two lines and change the third:

ssl_tlsv1_2=YES
ssl_tlsv1_1=YES
ssl_tlsv1=NO

Note that these options are only available with a patched version of vsftpd, and seems to be only installed on CentOS, and specifically not on Ubuntu. Other distributions may have the patched version as well.

Answer 2

It seems the current official version 3.0.3 actually works fine without the RHEL patch as it seems you do can limit connection to TLSv1.2.
As @Chris Kennedy write, you can set the following option in the config-file:

#Options: SSLv3, TLSv1.0, TLSv1.2, HIGH (see man ciphers)
ssl_ciphers=TLSv1.2

WinSCP Client test results:

Set client to Max SSL 3.0:
Connection failed

Set client to Max TLS 1.0:
Connection failed

Set client to Max TLS 1.1
Connection failed

Set client to Max TLS 1.2:
Connection succeed!

Log from WinSCP ver. 5.15.3 with TLS 1.2 connection:

...
. 2020-02-06 15:50:21.774 TLS connect: SSLv3 read server hello A
. 2020-02-06 15:50:21.775 TLS connect: SSLv3 read finished A
. 2020-02-06 15:50:21.775 TLS connect: SSLv3 write change cipher spec A
. 2020-02-06 15:50:21.775 TLS connect: SSLv3 write finished A
. 2020-02-06 15:50:21.775 TLS connect: SSLv3 flush data
. 2020-02-06 15:50:21.775 Using TLSv1.2, cipher TLSv1/SSLv3: ECDHE-RSA-AES256-GCM-        SHA384, 2048 bit RSA, ECDHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH     Au=RSA  Enc=AESGCM(256) Mac=AEAD
. 2020-02-06 15:50:21.775 TLS connection established

I did also play around with the other TLSv1.2, TLSv1.0, SSLv3 option-values, and they seem to be respected.

Answer 3

To limit VSFTPD to TLS 1.2, try setting: ssl_ciphers=TLSv1.2

I don't know if there's an easy way to limit the connection to TLS 1.1 and 1.2.

Answer 4

The vsftpd options of ssl_tlsv1_1 and ssl_tlsv1_2 appear to have been introduced in a patch called vsftpd-2.2.2-tlsv1_2.patch that is included in the vsftpd source code for RHEL-based distributions (checked on CentOS 7). The official vsftpd website and source code from Ubuntu repositories do not appear to include this patch or these tunable options (checked on Ubuntu 18.04).