Forum Discussion
AltostratusHow to disable CIPHER for and Disable TCP time stamp on F5 ?
Hi, We have just being chased by PCI Compliance about having vulnerabily that detected WEAK CIPHER support and TCP Timestamp being turned ON.
--Report say our application:
Negotiated with the following insecure cipher suites. SSLv3 ciphers:
Š SSL_RSA_WITH_RC4_128_SHA
TLS/SSL Server Supports Weak Cipher Algorithms
Solution:
Configure the server to disable support for weak ciphers.
For Apache web servers with mod_ssl, edit the Apache configuration file and change the
SSLCipherSuite line to read:
SSLCipherSuite ALL:!aNULL:!eNULL:!LOW:!EXP:RC4+RSA:+HIGH:+MEDIUM
I have looked at some article and there are a few ways to do that. We are using DEFAULT Cipher in our SSL Client Profile so do we just change that to
DEFAULT:!SSLv3
or
Replace DEFALUT with their suggested CIPHER
ALL:!aNULL:!eNULL:!LOW:!EXP:RC4+RSA:+HIGH:+MEDIUM
Please advice.
With TCP time stamp we have disabled this from the Application servers but it looks like this is turned ON in F5 for High Performance.
17 Replies
nitass_89166Noctilucent
i normally see people using cipher string from this sol if there is no special requirement.
sol13171: Configuring the cipher strength for SSL profiles (11.x)
http://support.f5.com/kb/en-us/solutions/public/13000/100/sol13171.htmlfor tcp timestamp, is it this one?
TCP timestamp response
http://www.rapid7.com/db/vulnerabilities/generic-tcp-timestampsol8072: Obtaining uptime information from TCP timestamps
http://support.f5.com/kb/en-us/solutions/public/8000/000/sol8072.html- Moinul_RonyThanks, on another point PCI scan pointed out absense of "Forward Secrecy with the reference browsers". Can this be implemented/enforced via F5?
- nitass_89166dh is natively supported in 11.2.1 Diffie-Hellman SSL key exchange cipher The Diffie-Hellman SSL key exchange cipher, which provides perfect forward secrecy (PFS), is now included natively. This provides better performance for configurations using Diffie-Hellman, especially on physical platforms that have hardware SSL acceleration. Release Note: BIG-IP LTM and TMOS 11.2.1 http://support.f5.com/kb/en-us/products/big-ip_ltm/releasenotes/product/relnote-ltm-11-2-1.html
- Moinul_RonyUnfortunately we are using 11.2.0. Any chance to enforce DH ?
- nitass
Employee
i normally see people using cipher string from this sol if there is no special requirement.
sol13171: Configuring the cipher strength for SSL profiles (11.x)
http://support.f5.com/kb/en-us/solutions/public/13000/100/sol13171.htmlfor tcp timestamp, is it this one?
TCP timestamp response
http://www.rapid7.com/db/vulnerabilities/generic-tcp-timestampsol8072: Obtaining uptime information from TCP timestamps
http://support.f5.com/kb/en-us/solutions/public/8000/000/sol8072.html- Moinul_RonyThanks, on another point PCI scan pointed out absense of "Forward Secrecy with the reference browsers". Can this be implemented/enforced via F5?
- nitassdh is natively supported in 11.2.1 Diffie-Hellman SSL key exchange cipher The Diffie-Hellman SSL key exchange cipher, which provides perfect forward secrecy (PFS), is now included natively. This provides better performance for configurations using Diffie-Hellman, especially on physical platforms that have hardware SSL acceleration. Release Note: BIG-IP LTM and TMOS 11.2.1 http://support.f5.com/kb/en-us/products/big-ip_ltm/releasenotes/product/relnote-ltm-11-2-1.html
- Moinul_RonyUnfortunately we are using 11.2.0. Any chance to enforce DH ?
mimlo_61970Cumulonimbus
Security through obscurity...
Anyway it looks like they added the option to disable this. In version 11.4.0 and up they seperated window scaling from timestamp for the high performance options in the TCP Profile.
See http://support.f5.com/kb/en-us/solutions/public/7000/500/sol7559.html
Still not recomended to disable, but if you cannot accept the risk with PCI at least you have the option. Is this coming up in a formal audit, or just a security scan? I don't think PCI strictly states this option must be off, and thus it is open to each auditor/penetration test to decide. I'd push back on them, and use sol8072 above as suporting evidence.
- mimlo_61970Also, find out what ciphers they are considering weak. RC4 with TLS1.1 and above seems to be highly out of favor, but the last time I asked support about it they could not disable RC4 for just TLS1.1 and above, you had to disable it completely. You can go to ssllabs.com and put in your website and get their assessment of it with some recomendations.
J_48024Nimbostratus
After lots of trials and error the following strings works for me. Citrix web interface though worked with other strings but Citrix Receiver was taking tooo long to "negotiation capabilities" ; with below string - everything is within acceptable limits..
TLSv1_2:TLSv1_1:TLSv1:@STRENGTH:!MD5:!EXPORT:!DES:!DHE:!EDH:!RC4:!ADH
