CVE-2026-42257: Ruby-Lang Net::imap

Critical severity, CVSS 9.8. EPSS: 0.5% chance of exploitation in the next 30 days.

Net::IMAP implements Internet Message Access Protocol (IMAP) client functionality in Ruby. Prior to versions 0.4.24, 0.5.14, and 0.6.4, several Net::IMAP commands accept a raw string argument that is sent to the server without validation or escaping. If this string is derived from user-controlled input, it may contain contain CRLF sequences, which an attacker can use to inject arbitrary IMAP commands. This issue has been patched in versions 0.4.24, 0.5.14, and 0.6.4.

Affected products

• Ruby-Lang Net::imap: before 0.4.24 (fixed in 0.4.24); from 0.5.0, before 0.5.14 (fixed in 0.5.14); from 0.6.0, before 0.6.4 (fixed in 0.6.4)

Published 2026-05-09. Last modified 2026-07-24.