Firewall Log Retention: Beyond The Guidance
In the absence of specific guidance, organizations are left to use their judgement in retaining logs…
Another one of those Dan’s New Leaf Posts, meant to inspire thought about IT Governance . . . .
Not long ago a Client asked for my input on their firewall log policy, as they were collecting logs but were unsure about how long they needed to retain them.
Interestingly, we too have still not found exactly how long a bank should retain their firewall logs or, for that matter, other logs. The guidance does require us to collect and analyze logs, but does not specify how long we must keep the logs. Specifically, the FFIEC says this:
“Regardless of the method of log management, management should develop processes to collect, aggregate, analyze, and correlate security information. Policies should define retention periods for security and operational logs.“
Just recently we asked two different examiners from two different FFIEC agencies, who need to remain “anonymous*,” how long event logs should be retained. We received these replies:
“To my knowledge, regulatory guidance does not dictate the duration that ‘key event logs’ should be retained. Industry best practice tends to support a one year time horizon, or at least until the area is subject to subsequent independent review/audit.”
“That is correct. One year is generally a ‘best practice’ minimum. Some organizations are saving them longer due to the low cost of storage media for potential forensics value.”
Based on this, we believe that from a regulatory standpoint how long you keep logs is up to you, but you should have a method to the madness…and now that the Cybersecurity Assessment Tool is in place you should document what you require.
We think that is a good thing, because if we can not keep logs for some reason, we can carve those logs out in our policy. But we also believe that while the regulators have no definite length of time for retention that logs should be kept, for forensics purposes, indefinitely. We want the ability, in ten years, to prove the context of the environment we’re managing today. That is what logs are for.
Therefore, we store 395 days (a year and one month), and then encourage our Clients to put a copy of the logs in their normal backup system, so that they would be retained “indefinitely.” Yes, by “indefinitely,” we mean “forever.”
So, in summary: the policy should say one year, your requirement from your MSSP should be more than one year, and in practice they should be retained indefinitely.
* Neither of these two examiners are in the examination team that completed infotex’ most recent FFIEC examination.
Original article by Dan Hadaway CRISC CISA CISM. Founder and Managing Partner, infotex
Dan’s New Leaf is a fun blog to inspire thought in the area of IT Governance.