GnuTLS 3.6.x before 3.6.14 uses incorrect cryptography for encrypting a session ticket (a loss of confidentiality in TLS 1.2, and an authentication bypass in TLS 1.3). The earliest affected version is 3.6.4 (2018-09-24) because of an error in a 2018-09-18 commit. Until the first key rotation, the TLS server always uses wrong data in place of an encryption key derived from an application. A flaw was found in GnuTLS, in versions starting from 3.6.4, where it does not session the ticket encryption key in a secure fashion by the application which is connecting. This flaw allows an attacker to craft a man-in-the-middle-attack, with the ability to bypass the TLS1.3 authentication and also recover older conversations when TLS1.2 is in use. The highest threat to this flaw is to confidentiality and integrity.
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