Files
zulip/scripts/setup/configure-rabbitmq
Alex Vandiver a5496f4098 CVE-2021-43799: Set a secure Erlang cookie.
The RabbitMQ docs state ([1]):

    RabbitMQ nodes and CLI tools (e.g. rabbitmqctl) use a cookie to
    determine whether they are allowed to communicate with each
    other. [...] The cookie is just a string of alphanumeric
    characters up to 255 characters in size. It is usually stored in a
    local file.

...and goes on to state (emphasis ours):

    If the file does not exist, Erlang VM will try to create one with
    a randomly generated value when the RabbitMQ server starts
    up. Using such generated cookie files are **appropriate in
    development environments only.**

The auto-generated cookie does not use cryptographic sources of
randomness, and generates 20 characters of `[A-Z]`.  Because of a
semi-predictable seed, the entropy of this password is thus less than
the idealized 26^20 = 94 bits of entropy; in actuality, it is 36 bits
of entropy, or potentially as low as 20 if the performance of the
server is known.

These sizes are well within the scope of remote brute-force attacks.

On provision, install, and upgrade, replace the default insecure
20-character Erlang cookie with a cryptographically secure
255-character string (the max length allowed).

[1] https://www.rabbitmq.com/clustering.html#erlang-cookie
2022-01-25 02:13:53 +00:00

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#!/usr/bin/env bash
#
# Delete the "guest" default user and replace it with a Zulip user
# with a real password
set -eu
if [ "$EUID" -eq 0 ]; then
sudo=()
else
sudo=(sudo)
fi
# If the RabbitMQ distribution cookie is insecure, reset it and
# restart RabbitMQ.
"${sudo[@]}" "$(dirname "$0")/generate-rabbitmq-cookie"
RABBITMQ_USERNAME=$("$(dirname "$0")/../get-django-setting" RABBITMQ_USERNAME)
RABBITMQ_PASSWORD=$("$(dirname "$0")/../get-django-setting" RABBITMQ_PASSWORD)
# Wait for RabbitMQ to start up
try_ping() {
# `rabbitmqctl ping` requires 3.7.6 or newer
out="$("${sudo[@]}" rabbitmqctl eval 'net_adm:ping(node()).')" && [ "$out" = 'pong' ]
}
retries=29
while ! try_ping 2>/dev/null; do
sleep 1
if ! ((retries -= 1)); then
try_ping
break
fi
done
"${sudo[@]}" rabbitmqctl delete_user "$RABBITMQ_USERNAME" || true
"${sudo[@]}" rabbitmqctl delete_user zulip || true
"${sudo[@]}" rabbitmqctl delete_user guest || true
"${sudo[@]}" rabbitmqctl add_user "$RABBITMQ_USERNAME" "$RABBITMQ_PASSWORD"
"${sudo[@]}" rabbitmqctl set_user_tags "$RABBITMQ_USERNAME" administrator
"${sudo[@]}" rabbitmqctl set_permissions -p / "$RABBITMQ_USERNAME" '.*' '.*' '.*'