In fetchmail before 6.5.6, the SMTP client can crash when authenticating upon receiving a 334 status code in a malformed context.
https://www.openwall.com/lists/oss-security/2025/10/03/2
https://www.fetchmail.info/fetchmail-SA-2025-01.txt
https://gitlab.com/fetchmail/fetchmail/-/commit/4c3cebfa4e659fb778ca2cae0ccb3f69201609a8