Cookbook/Firewalling Notes

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Run KDB as a separate (non-root) user. If you need it to run on port 80, use authbind or iptables redirect

Do not allow that user to write to any directory or files: If you need file access, arbitrate it via IPC with another KDB process. Pay attention to how that process will return values via or or similar.

Firewall ALL ports inbound/outbound except ones explicitly used (hint: use iptables owner match). For any backend KDB processes, restrict them to localhost or a protected network (e.g. iptables --pol ipsec)

Set process limits with ulimit no larger than you need them

Restrict input by defining at least:

If you want to allow certain IPC calls, implement only the ones you want: Trying to blacklist functions is tricky because some otherwise useful functions may have a mode that accesses the disk which may cause information leak (e.g. key). It is much easier to use a whitelist approach. The Q for Gods Whitepaper (ยง6) has some suggested guidance here.

As IPC functions either receive a parse tree or a string (that you could parse yourself), make sure you check the type of the input e.g. x:$[10h=type x;parse x;x]

If you use websockets, define:

When handling untrusted input, consider designing your application to wrap public entrypoints with reval.

Pay attention to the fact that each websocket client can open up a lot (200 on Mozilla, 256 for Chrome) of websocket connections, so limit using .z.a

Log connections and consider using fail2ban to block suspicious traffic.

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