RabbitMQ is a messaging and streaming broker. Prior to versions 3.13.15, 4.0.20, 4.1.11, 4.2.6, and 4.3.0, The trust-store plugin installs a verify fun that overrides {bad cert, unknown ca} / {bad cert, selfsigned peer} when the presented cert "matches" a whitelisted one. The match key is extract issuer id/1 → public key:pkix issuer id/2 → {IssuerName, SerialNumber} , both fields are taken verbatim from the presented certificate body and contain no public-key, SKI, fingerprint or signature material. is whitelisted/1 is a pure ets:member lookup; the stored full DER is used only for list/0 display and is never compared against the presented cert. cacerts is [], so the whitelisted cert is never used as a trust anchor for path validation either. TLS client-authentication bypass: an attacker who knows the issuer DN + serial of any whitelisted certificate can connect with a forged self-signed cert. Preconditions include rabbitmq trust store plugin enabled and used as the TLS verify fun Attacker knows or can guess the {Issuer, Serial} of at least one whitelisted cert (non-secret; exposed via CLI/logs/any cert copy). This issue is fixed in versions 3.13.15, 4.0.20, 4.1.11, 4.2.6, and 4.3.0.