It was discovered that Ruby's Net::IMAP library did not properly verify that Transport Layer Security (TLS) encryption was started after issuing a STARTTLS command. A remote attacker could possibly use this issue to perform a machine-in-the-middle attack and silently bypass TLS encryption. ( CVE-2026-42246 ) It was also discovered that Ruby's Net::IMAP library did not validate string arguments passed to certain commands. A remote attacker could possibly use this issue to inject arbitrary IMAP commands. ( CVE-2026-42257 )
It was discovered that Ruby's Net::IMAP library did not properly verify that Transport Layer Security (TLS) encryption was started after issuing a STARTTLS command. A remote attacker could possibly use this issue to perform a machine-in-the-middle attack and silently bypass TLS encryption. ( CVE-2026-42246 )
It was also discovered that Ruby's Net::IMAP library did not validate string arguments passed to certain commands. A remote attacker could possibly use this issue to inject arbitrary IMAP commands. ( CVE-2026-42257 )
It was discovered that Ruby's Net::IMAP library did not properly verify that Transport Layer Security (TLS) encryption was started after issuing a STARTTLS command. A remote attacker could possibly use this issue to perform a machine-in-the-middle attack and silently bypass TLS encryption. ( CVE-2026-42246 ) It was also discovered that Ruby's Net::IMAP library did not validate string arguments passed to certain commands. A remote attacker could possibly use this issue to inject arbitrary IMAP commands. ( CVE-2026-42257 )
It was discovered that Ruby's Net::IMAP library did not properly verify that Transport Layer Security (TLS) encryption was started after issuing a STARTTLS command. A remote attacker could possibly use this issue to perform a machine-in-the-middle attack and silently bypass TLS encryption. ( CVE-2026-42246 )
It was also discovered that Ruby's Net::IMAP library did not validate string arguments passed to certain commands. A remote attacker could possibly use this issue to inject arbitrary IMAP commands. ( CVE-2026-42257 )
In general, a standard system update will make all the necessary changes.
The problem can be corrected by updating your system to the following package versions:
Ubuntu Pro provides ten-year security coverage to 25,000+ packages in Main and Universe repositories, and it is free for up to five machines.
The full story
This article is one source in a clustered incident — the cluster page carries the summary, timeline and every other outlet covering it.
