RabbitMQ is a messaging and streaming broker. From 4.2.0 until 4.2.8 and 4.3.2, get auth mechanism/1 used term to binary/1 on the strict auth mechanism or preferred auth mechanism atom when clearing the corresponding cookie, producing a non-ASCII cookie name that violates RFC 6265 and can prevent the browser from deleting the preference. The issue is not directly exploitable for code execution or data exfiltration; its security relevance is limited to stale authentication-mechanism preferences persisting across logout and login cycles. This issue is fixed in versions 4.2.8 and 4.3.2.