RHSA-2026:76763 - Security Advisory

Topic

An update for dovecot is now available for Red Hat Enterprise Linux 8.

Red Hat Product Security has rated this update as having a security impact of Important. A Common Vulnerability Scoring System (CVSS) base score, which gives a detailed severity rating, is available for each vulnerability from the CVE link(s) in the References section.

Description

Dovecot is an IMAP server for Linux and other UNIX-like systems, written primarily with security in mind. It also contains a small POP3 server, and supports e-mail in either the maildir or mbox format. The SQL drivers and authentication plug-ins are provided as subpackages.

Security Fix(es):

• dovecot: Dovecot: Denial of Service via IMAP ID command with excessive parameters (CVE-2026-42391)
• dovecot: Dovecot: Authentication bypass via incorrect OAuth2 token validation (CVE-2026-73208)
• dovecot: Dovecot: Denial of service via crafted email headers (CVE-2026-27852)
• dovecot: Dovecot: Denial of Service via truncated quoted argument in ManageSieve (CVE-2026-40019)
• dovecot: Dovecot: Denial of Service and potential message duplication via connection limit exhaustion (CVE-2026-33263)
• dovecot: Dovecot: Denial of Service in ManageSieve login process (CVE-2026-33605)
• dovecot: Dovecot: Arbitrary Code Execution via Sieve editheader use-after-free (CVE-2026-42007)
• dovecot: Dovecot: MySQL multi-byte escaping wrong (CVE-2026-40018)

Bug Fix(es) and Enhancement(s):

• Dovecot crashes when accessing mailbox with: "Panic: file mail-user.c: line 229 (mail_user_deinit): assertion failed: ((*user)->refcount == 1)" (JIRA:RHEL-176273)

For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

Solution

For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

Affected Products

• Red Hat Enterprise Linux for x86_64 8 x86_64
• Red Hat Enterprise Linux for IBM z Systems 8 s390x
• Red Hat Enterprise Linux for Power, little endian 8 ppc64le
• Red Hat Enterprise Linux for ARM 64 8 aarch64
• Red Hat CodeReady Linux Builder for x86_64 8 x86_64
• Red Hat CodeReady Linux Builder for Power, little endian 8 ppc64le
• Red Hat CodeReady Linux Builder for ARM 64 8 aarch64
• Red Hat CodeReady Linux Builder for IBM z Systems 8 s390x
• Red Hat Enterprise Linux for x86_64 - Extended Life Cycle 8.10 x86_64
• Red Hat Enterprise Linux for ARM 64 - Extended Life Cycle 8.10 aarch64
• Red Hat Enterprise Linux for Power, little endian - Extended Life Cycle 8.10 ppc64le
• Red Hat Enterprise Linux for IBM z Systems - Extended Life Cycle 8.10 s390x

Fixes

• BZ - 2525545 - CVE-2026-42391 dovecot: Dovecot: Denial of Service via IMAP ID command with excessive parameters
• BZ - 2525547 - CVE-2026-73208 dovecot: Dovecot: Authentication bypass via incorrect OAuth2 token validation
• BZ - 2525557 - CVE-2026-27852 dovecot: Dovecot: Denial of service via crafted email headers
• BZ - 2525559 - CVE-2026-40019 dovecot: Dovecot: Denial of Service via truncated quoted argument in ManageSieve
• BZ - 2525567 - CVE-2026-33263 dovecot: Dovecot: Denial of Service and potential message duplication via connection limit exhaustion
• BZ - 2525576 - CVE-2026-33605 dovecot: Dovecot: Denial of Service in ManageSieve login process
• BZ - 2525583 - CVE-2026-42007 dovecot: Dovecot: Arbitrary Code Execution via Sieve editheader use-after-free
• BZ - 2525584 - CVE-2026-40018 dovecot: Dovecot: MySQL multi-byte escaping wrong
• RHEL-176273 - Dovecot crashes when accessing mailbox with: "Panic: file mail-user.c: line 229 (mail_user_deinit): assertion failed: ((*user)->refcount == 1)"

CVEs

• CVE-2026-27852
• CVE-2026-33263
• CVE-2026-33605
• CVE-2026-40018
• CVE-2026-40019
• CVE-2026-42007
• CVE-2026-42391
• CVE-2026-73208

References

• https://access.redhat.com/security/updates/classification/#important