STARTTLS implementations in email clients & servers plagued by 40+ vulnerabilities

If Thunderbird is configured to use STARTTLS for an IMAP server, and the server sends a PREAUTH response, then Thunderbird will continue with an unencrypted connection, causing email data to be sent without protection. This vulnerability affects Thunderbird < 68.9.0.

Mutt before 1.14.3 allows an IMAP fcc/postpone man-in-the-middle attack via a PREAUTH response.

evolution-data-server (eds) through 3.36.3 has a STARTTLS buffering issue that affects SMTP and POP3. When a server sends a "begin TLS" response, eds reads additional data and evaluates it in a TLS context, aka "response injection."

Alpine before 2.23 silently proceeds to use an insecure connection after a /tls is sent in certain circumstances involving PREAUTH, which is a less secure behavior than the alternative of closing the connection and letting the user decide what they would like to do.

Mutt before 1.14.4 and NeoMutt before 2020-06-19 have a STARTTLS buffering issue that affects IMAP, SMTP, and POP3. When a server sends a "begin TLS" response, the client reads additional data (e.g., from a man-in-the-middle attacker) and evaluates it in a TLS context, aka "response injection."

MSA/SMTP.cpp in Trojita before 0.8 ignores certificate-verification errors, which allows man-in-the-middle attackers to spoof SMTP servers.

During the plaintext phase of the STARTTLS connection setup, protocol commands could have been injected and evaluated within the encrypted session. This vulnerability affects Thunderbird < 78.7.

common/session.c in Claws Mail before 3.17.6 has a protocol violation because suffix data after STARTTLS is mishandled.

LibEtPan through 1.9.4, as used in MailCore 2 through 0.6.3 and other products, has a STARTTLS buffering issue that affects IMAP, SMTP, and POP3. When a server sends a "begin TLS" response, the client reads additional data (e.g., from a meddler-in-the-middle attacker) and evaluates it in a TLS context, aka "response injection."

KDE KMail 19.12.3 (aka 5.13.3) engages in unencrypted POP3 communication during times when the UI indicates that encryption is in use.

In s/qmail through 4.0.07, an active MitM can inject arbitrary plaintext commands into a STARTTLS encrypted session between an SMTP client and s/qmail. This allows e-mail messages and user credentials to be sent to the MitM attacker.

In GNOME evolution-data-server before 3.35.91, a malicious server can crash the mail client with a NULL pointer dereference by sending an invalid (e.g., minimal) CAPABILITY line on a connection attempt. This is related to imapx_free_capability and imapx_connect_to_server.

In GNOME Balsa before 2.6.0, a malicious server operator or man in the middle can trigger a NULL pointer dereference and client crash by sending a PREAUTH response to imap_mbox_connect in libbalsa/imap/imap-handle.c.

GNOME Geary before 3.36.3 mishandles pinned TLS certificate verification for IMAP and SMTP services using invalid TLS certificates (e.g., self-signed certificates) when the client system is not configured to use a system-provided PKCS#11 store. This allows a meddler in the middle to present a different invalid certificate to intercept incoming and outgoing mail.

This issue was addressed with improved checks. This issue is fixed in macOS Catalina 10.15.7, Security Update 2020-005 High Sierra, Security Update 2020-005 Mojave. A remote attacker may be able to unexpectedly alter application state.

If Thunderbird was configured to use STARTTLS for an IMAP connection, and an attacker injected IMAP server responses prior to the completion of the STARTTLS handshake, then Thunderbird didn't ignore the injected data. This could have resulted in Thunderbird showing incorrect information, for example the attacker could have tricked Thunderbird to show folders that didn't exist on the IMAP server. This vulnerability affects Thunderbird < 78.12.

An attacker in a privileged network position may be able to misrepresent application state. This issue is fixed in macOS Big Sur 11.4, Security Update 2021-003 Catalina, Security Update 2021-004 Mojave. A logic issue was addressed with improved state management.