Medium [CVE-2026-47240] Net::IMAP: Command injection via non-synchronizing literals

Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. Prior to 0.6.5 and 0.5.15, several Net::IMAP commands accept a "raw data" argument that is sent verbatim after validation to prevent command injection.

However, if a server does not support non-synchronizing literals, it may still be possible to inject arbitrary IMAP commands inside non-synchronizing literals. A server without support for non-synchronizing literals may interpret the "+}\r\n" as the end of a malformed command line and respond with a tagged BAD.

In that case, the contents of the literal will be interpreted as one or more new pipelined commands, allowing a CRLF command injection attack to succeed. This affects criteria for #search and #uid_search; search_keys for #sort, #thread, #uid_sort, and #uid_thread; and attr for #fetch and #uid_fetch.

This vulnerability is fixed in 0.6.5 and 0.5.15. This command injection could enable unauthorized actions on the IMAP server.

This Moderate flaw in the Net::IMAP Ruby library allows for command injection against IMAP servers that lack support for non-synchronizing literals. An attacker could exploit this by providing specially crafted input, leading to the execution of arbitrary IMAP commands and potential unauthorized actions.