The Net::IMAP library accepts raw string arguments in several IMAP commands and only validates them to prevent CRLF injection. If an attacker supplies a user‑controlled raw string, the next IMAP command may be interpreted as a continuation of the first command. This causes the original command to eventually fail and prevents it from returning until another command is sent from another thread. That other command will not return until the connection is closed, resulting in a denial‑of‑service condition for the client application.

The issue affects the Ruby Net::IMAP client. Versions prior to 0.6.5 for the 0.6 branch and prior to 0.5.15 for the 0.5 branch are vulnerable. Upgrading to 0.6.5 or 0.5.15, respectively, resolves the vulnerability.

The CVSS score of 2.1 indicates a low severity impact, while the EPSS score of < 1% means that the exploitation probability is very low. This vulnerability is not listed in CISA’s KEV catalog. The problem arises from improper raw argument validation, which is categorized by CWEs 162, 182, 186, and 88. The most likely attack vector is an application that forwards untrusted input directly to the Net::IMAP library, allowing an attacker to send crafted IMAP commands from a user‑controlled context. Because the exploit requires a specific client use case, the risk of widespread exploitation is limited, but it can still cause a denial of service to the impacted application.