eventlet before 0.35.2, as used in dnspython before 2.6.0, allows remote attackers to interfere with DNS name resolution by quickly sending an invalid packet from the expected IP address and source port, aka a "TuDoor" attack. In other words, dnspython does not have the preferred behavior in which the DNS name resolution algorithm would proceed, within the full time window, in order to wait for a valid packet. NOTE: dnspython 2.6.0 is unusable for a different reason that was addressed in 2.6.1. The dnspython stub resolver is vulnerable to a denial of service (DoS) risk if an attacker sends a malicious response forged with the correct address and port before a legitimate one arrives on the UDP port used by dnspython for the query. In such cases, dnspython could either switch to another resolver or abandon the query altogether, potentially leading to service denial for that resolution.
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