Data center servers may obtain software updates or certificate
status from servers on the internet. The greatest risk is connecting
to the wrong server. Create strict whitelist rules for updates to
limit the reachable external servers and the allowed applications
(on default ports only). This prevents infected data center servers from
phoning home and prevents data exfiltration using legitimate applications
such as FTP, HTTP, or DNS on non-standard ports. In addition, use
the File Blocking profile’s
to block outbound update files so you only allow downloading for
software update files.
For each rule, apply best practice
Security profiles and configure
Log at Session End
Work with engineering
and other groups that update software to log and analyze web browsing
sessions to define the URLs to which developers connect for updates.
These examples allow engineering
servers to communicate with CentOS update servers (
Allow connecting to an internet Online Certificate Status Protocol (OCSP)
Responder to check the revocation status of authentication certificates
and ensure they are valid. When you configure a certificate profile on the
firewall, set up CRL status verification as a fallback method for
OCSP in case the OCSP Responder is unreachable.
Create data-center-to-internet Decryption policy rules
to decrypt the traffic allowed in the preceding Security policy
A compromised update server could download malware and
propagate it through the software update process, so decrypting
traffic to gain visibility is critical. Because only service accounts
initiate update traffic and update traffic has no personal or sensitive
information, there are no privacy issues.
traffic to OCSP certificate revocation servers because the traffic
usually uses HTTP, so it’s not encrypted. In addition, SSL Forward
Proxy decryption may break the update process because the firewall acts
as a proxy and replaces the client certificate with a proxy certificate,
which the OCSP responder may not accept as valid.
Decrypt traffic between
data center and update servers. These two examples decrypt the CentOS
and Windows update traffic allowed by the analogous Security policy
rules in the preceding step.
Decrypt traffic between data center servers and NTP and DNS
update servers. This example decrypts the update traffic allowed
by the analogous Security policy rule in the preceding step.