Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. Starting in version 0.3.2 and prior to versions 0.3.8, 0.4.19, and 0.5.6, there is a possibility for denial of service by memory exhaustion in "net-imap"'s response parser. At any time while the client is connected, a malicious server can send can send highly compressed "uid-set" data which is automatically read by the client's receiver thread. The response parser uses "Range#to_a" to convert the "uid-set" data into arrays of integers, with no limitation on the expanded size of the ranges. Versions 0.3.8, 0.4.19, 0.5.6, and higher fix this issue. Additional details for proper configuration of fixed versions and backward compatibility are available in the GitHub Security Advisory.