Net::IMAP: Command Injection via ID command argument

### Summary Two `Net::IMAP` commands, `#id` and `#enable`, do not validate their arguments. Arguments to either command could be used by an attacker to inject arbitrary IMAP commands. Please note that passing untrusted inputs to these commands is usually inappropriate and expected to be uncommon. ### Details When `Net::IMAP#id` is called with a hash argument, although the ID field value strings are correctly quoted (escaping quoted specials), they were not validated to prohibit CRLF sequences. While `Net::IMAP#enable` does process its arguments for aliases, it does not validate them as valid atoms (or as a list of valid atoms). The `#to_s` value is sent verbatim. ### Impact This is expected to impact very few users: use of untrusted user input for either command is expected to be very uncommon. The documentation for `#enable` explicitly warns that using any arguments that are not in the explicitly supported list may result in undocumented behavior. Using arbitrary untrusted user input for `#enable` will always be inappropriate. Although client ID field values will most commonly be static and hardcoded, dynamic input sources may be used. For example, client ID fields may be set by configuration or version numbers. Using untrusted user inputs for client ID fields is expected to be uncommon. But any untrusted inputs to client ID can trivially exploit this vulnerability. Untrusted inputs to either command may include a CRLF sequence followed by a new IMAP command (like DELETE mailbox). Although this does not directly enable data exfiltration, it could be combined with other attack vectors or knowledge of the target system's attributes, e.g.: shared mail folders or the application's installed response handlers. ### Mitigation Update to a version of `net-imap` which validates `#id` and `#enable` arguments. Untrusted inputs should _never_ be used for `#enable` arguments. If `net-imap` cannot be upgraded: * do not use untrusted inputs for client ID field values * or add validation that client ID field values must not contain any CR or LF bytes.

Quoted source text, attributed separately from HOL analysis.