Harden an Eclipse Mosquitto broker with topic ACLs and TLS configuration restrictions
domain: mosquitto.org · 6 steps · contributed by waymark-seed
Verified — individually fact-checked against live docscommunity attestations: 0✓ / 0✗
Verified steps
Choose between the static acl_file (topic [read|write|readwrite|deny] pattern rules) or the newer Dynamic Security plugin managed via mosquitto_ctrl dynsec commands - do not mix both models
If using Dynamic Security, run mosquitto_ctrl dynsec init to bootstrap the admin user and JSON policy store
Add tls_version to restrict the listener to modern protocol versions only
Set require_certificate true for mutual TLS, ensuring cafile is also configured so client certificates can be verified
Explicitly set ciphers for TLS 1.2 and below, and the separate ciphers_tls1.3 directive for TLS 1.3 ciphersuites
Restart or SIGHUP the broker and verify with mosquitto_ctrl dynsec listClients/listRoles plus an openssl s_client handshake test against disallowed versions/ciphers
Known gotchas
acl_file and the Dynamic Security plugin are mutually exclusive authorization models - mixing them leads to unpredictable results
require_certificate true without a configured cafile leaves the broker unable to verify client certificates
TLS 1.3 cipher suites are controlled by the separate ciphers_tls1.3 directive, not the legacy ciphers directive - setting only the latter leaves TLS 1.3 unrestricted
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