An attacker that holds a token intended for a different purpose can authenticate, because when an OAuth2 token response does not contain a scope claim, the audience claim is used in its place and checked against the configured required scopes. These are different concepts, and the audience claim does not describe what a token is allowed to do. A token that grants no relevant permissions can be accepted because its intended recipient value happens to match a configured scope name, granting access that should have been denied. It also hides an identity provider misconfiguration where scopes are not being issued at all. Ensure the identity provider issues a scope claim for all tokens used with Dovecot, and that configured scope names do not match audience values. Update to non-vulnerable version. No publicly available exploits are known.

alma_linux ALSA-2026:79371: ALSA-2026:79371: dovecot security update (High)

The remote Oracle Linux 10 host has packages installed that are affected by multiple vulnerabilities as referenced in the ELSA-2026-79371 advisory.

    - fix CVE-2026-33605: ManageSieve: denial of service via lone CR       character causing protocol deadlock (RHEL-251984)
    - fix CVE-2026-42007: fix use-after-free and info leak in sieve       editheader extension (RHEL-251945)
    - fix CVE-2026-40018: incorrect escaping of multi-byte strings in SQL commands (RHEL-252058)
    - fix CVE-2026-42391: fix excessive memory growth with pre-login ID       command (RHEL-252072)
    - fix CVE-2026-73208: OAuth2 scope check requires all configured scopes, add oauth2_audience setting     (RHEL-251900)
    - fix CVE-2026-27852: limit parsed message data to prevent memory exhaustion (RHEL-251564)

Tenable has extracted the preceding description block directly from the Oracle Linux security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The remote Redhat Enterprise Linux 10 host has packages installed that are affected by multiple vulnerabilities as referenced in the RHSA-2026:79371 advisory.

    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)

    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.

Tenable has extracted the preceding description block directly from the Red Hat Enterprise Linux security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The Rocky Linux 8 host has packages installed that are affected by multiple vulnerabilities as referenced in the CIQ crlsa-2026_76763 advisory.

    * 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:Rocky Linux-176273)

Tenable has extracted the preceding description block directly from the CIQ security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The remote AlmaLinux 8 host has packages installed that are affected by multiple vulnerabilities as referenced in the ALSA-2026:76763 advisory.

    * 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:AlmaLinux-176273)

Tenable has extracted the preceding description block directly from the AlmaLinux security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The remote Oracle Linux 8 host has packages installed that are affected by multiple vulnerabilities as referenced in the ELSA-2026-76763 advisory.

    - fix CVE-2026-33605: ManageSieve login deadlock caused by lone CR       protocol violation (RHEL-251995)
    - fix CVE-2026-42007: heap use-after-free in pigeonhole edit_mail_snapshot       after deleteheader operation (RHEL-251946)
    - fix CVE-2026-40018: incorrect escaping of multi-byte strings in SQL commands (RHEL-252064)
    - fix CVE-2026-42391: pre-auth CPU/memory amplification via       excessive ID command key/value pairs (RHEL-252056)
    - fix CVE-2026-73208: OAuth2 scope check requires all configured scopes, add oauth2_audience setting     (RHEL-251905)
    - fix CVE-2026-27852: denial of service via memory exhaustion from       crafted message headers (RHEL-251573)
    - fix CVE-2026-33263: submission-login panic at       mail_max_userip_connections limit (RHEL-251922)

Tenable has extracted the preceding description block directly from the Oracle Linux security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The remote RockyLinux 8 host has packages installed that are affected by multiple vulnerabilities as referenced in the RLSA-2026:76763 advisory.

    * 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:Rocky Linux-176273)

Tenable has extracted the preceding description block directly from the RockyLinux security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The remote Redhat Enterprise Linux 8 host has packages installed that are affected by multiple vulnerabilities as referenced in the RHSA-2026:76763 advisory.

    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.

Tenable has extracted the preceding description block directly from the Red Hat Enterprise Linux security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The remote Debian 13 host has packages installed that are affected by multiple vulnerabilities as referenced in the dsa-6526 advisory.

    - -------------------------------------------------------------------------     Debian Security Advisory DSA-6526-1                   security@debian.org     https://www.debian.org/security/                       Moritz Muehlenhoff     September 28, 2026                    https://www.debian.org/security/faq
    - -------------------------------------------------------------------------

    Package        : dovecot     CVE ID         : CVE-2026-27852 CVE-2026-33263 CVE-2026-33604 CVE-2026-33605                      CVE-2026-33606 CVE-2026-33607 CVE-2026-40013 CVE-2026-40014                      CVE-2026-40015 CVE-2026-40017 CVE-2026-40018 CVE-2026-40203                      CVE-2026-40204 CVE-2026-40205 CVE-2026-42007 CVE-2026-42008                      CVE-2026-42391 CVE-2026-42392 CVE-2026-42393 CVE-2026-42394                      CVE-2026-42395 CVE-2026-52681 CVE-2026-52687 CVE-2026-73208                      CVE-2026-73209     Debian Bug     : 1144639

    Multiple vulnerabilities have been discovered in the Dovecot IMAP server     which could result in denial of service, SMTP smuggling, information     disclosure, code injection via malformed Sieve scripts or bypass of ACL     restrictions.

    For the stable distribution (trixie), these problems have been fixed in     version 1:2.4.1+dfsg1-6+deb13u7.

    We recommend that you upgrade your dovecot packages.

    For the detailed security status of dovecot please refer to     its security tracker page at:
    https://security-tracker.debian.org/tracker/dovecot

    Further information about Debian Security Advisories, how to apply     these updates to your system and frequently asked questions can be     found at: https://www.debian.org/security/

    Mailing list: debian-security-announce@lists.debian.org

Tenable has extracted the preceding description block directly from the Debian security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The remote openSUSE 16 host has packages installed that are affected by multiple vulnerabilities as referenced in the openSUSE-SU-2026:21720-1 advisory.

    Update to 2.4.5.

    - CVE-2026-33263: `submission-login`: panic when `mail_max_userip_connections` is reached (bsc#1276794).
    - CVE-2026-27852: DoS by sending mail with bad header (bsc#1276799).
    - CVE-2026-33604: SMTP smuggling via missing dot-stuffing after bare carriage return (bsc#1276802).
    - CVE-2026-33605: `managesieve-login`: pre-auth crash (bsc#1276809).
    - CVE-2026-33606: `dsync`: mail content can cause `dsync` protocol injection (bsc#1276800).
    - CVE-2026-33607: IMAP `LIST` `match_sub()` exponential backtracking leading to CPU denial of service     (bsc#1276795).
    - CVE-2026-40013: stack buffer underflow in `pigeonhole` `ManageSieve` `CHECKSCRIPT/PUTSCRIPT`     (bsc#1276807).
    - CVE-2026-40014: CPU DoS via crafted references header (bsc#1276804).
    - CVE-2026-40015: `imap-hibernate` can be crashed (bsc#1276812).
    - CVE-2026-40017: CPU DoS via CRC32 hash collision in `strmap` (bsc#1276813).
    - CVE-2026-40018: MySQL multi-byte escaping performed incorrectly (bsc#1276810).
    - CVE-2026-40203: IMAP compression can reveal whether a small synced email body matches sender-chosen text       (bsc#1276815).
    - CVE-2026-40204: `lda_mailbox_autocreate` can bypass ACL restrictions (bsc#1276819).
    - CVE-2026-40205: OAuth2 `passdb` scope enforcement bypass via OR semantics in remote validation path     (bsc#1276820).
    - CVE-2026-42007: `sieve` `editheader` RCE (bsc#1276817).
    - CVE-2026-42008: `XCLIENT FORWARD= bare` token not namespaced (bsc#1276824).
    - CVE-2026-42391: `imap`: pre-login memory/CPU growth with `ID` command (bsc#1276835).
    - CVE-2026-42392: `imap-urlauth` leaks memory into user-visible error messages (bsc#1276829).
    - CVE-2026-42393: `doveadm_password` or api key length can be leaked with timing comparisons     (bsc#1276827).
    - CVE-2026-52687: `imap`: `COMPRESS ZSTD` can cause excessive memory usage (bsc#1276837).
    - CVE-2026-42395: single NUL-byte `XCLIENT FORWARD` payload crashes (bsc#1276826).
    - CVE-2026-52681: `sieve` resource usage tracking lost when active script changes (bsc#1276828).
    - CVE-2026-73208: `auth`: `db-oauth2`: `aud` claim used as fallback for missing scope claim (bsc#1276830).
    - CVE-2026-73209: `imap-login` crash due to self-recursion on zero-output decompress chunks (bsc#1276833).

Tenable has extracted the preceding description block directly from the SUSE security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

There are packages installed that are affected by multiple vulnerabilities referenced in the following CVEs:

  - An attacker that has valid credentials can use a Sieve script with the editheader extension to trigger a
    use-after-free in the mail editing code, and to write memory contents beyond the intended buffer into the
    delivered mail. This causes memory leak and opportunity to do memory corruption during mail delivery,
    which can crash the delivery process and may allow execution of arbitrary code in the context of that
    process. Disable the Sieve editheader extension. Update to non-vulnerable version. No publicly available
    exploits are known. (CVE-2026-42007)

  - An attacker that can send mail to a user can craft a message whose headers contain a very large number of
    email addresses or MIME parameters, which causes excessive memory usage when the message is later parsed.
    The message is still delivered, but reading it over IMAP can exhaust the memory limit of the process and
    terminate it, causing denial of service for the affected user. Update to non-vulnerable version. No
    publicly available exploits are known. (CVE-2026-27852)

  - When mail_max_userip_connections is set (default 10) and reached, submission-login can crash with epoll()
    panic caused by file descriptor handling issues. If running in high-security mode (default for community
    releases), only the new submission connection gets terminated. If running in high-performance mode
    (default for Pro releases), all connections handled by the submission-login process will be terminated.
    The crashes can cause failure for user to send a message, or it can cause duplicate messages to be sent.
    If TLS is not used (in the backend server processing the submission), duplicate deliveries cannot happen,
    because the crash can only happen at AUTH stage. Limit the number of connections handled by single
    submission-login process. This has a performance impact though. Update to non-vulnerable version. No
    publicly available exploits are known. (CVE-2026-33263)

  - An attacker that can get Dovecot to relay a message, for example through Sieve redirect or submission
    relay, can use a crafted line ending in the message body to bypass the outbound protection that prevents
    message content from being interpreted as SMTP commands. A downstream mail server that hasn't yet fixed
    the SMTP smuggling vulnerability can be tricked into treating part of the message body as new SMTP
    commands, allowing injection of spoofed email. This is the same vulnerability class as CVE-2023-51764 and
    CVE-2023-51766. Where you control the receiving mail servers, ensure they reject bare carriage returns in
    message data. Update to non-vulnerable version. No publicly available exploits are known. (CVE-2026-33604)

  - An unauthenticated attacker can crash the ManageSieve login process by sending a small malformed command
    before authenticating. If running in high-security mode (default for community releases), only the
    attacker's own connection is terminated. If running in high-performance mode (default for Pro releases),
    all connections handled by the same managesieve-login process are terminated. Repeating the attack can
    cause denial of service for Sieve script management. Restrict network access to the ManageSieve service to
    trusted clients. Update to non-vulnerable version. No publicly available exploits are known.
    (CVE-2026-33605)

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - An attacker that holds a token intended for a different purpose can authenticate, because when an OAuth2     token response does not contain a scope claim, the audience claim is used in its place and checked against     the configured required scopes. These are different concepts, and the audience claim does not describe     what a token is allowed to do. A token that grants no relevant permissions can be accepted because its     intended recipient value happens to match a configured scope name, granting access that should have been     denied. It also hides an identity provider misconfiguration where scopes are not being issued at all.
    Ensure the identity provider issues a scope claim for all tokens used with Dovecot, and that configured     scope names do not match audience values. Update to non-vulnerable version. No publicly available exploits     are known. (CVE-2026-73208)

Note that Nessus relies on the presence of the package as reported by the vendor.

ID	Name	Product	Family	Type	Severity
364354	Oracle Linux 10 : dovecot (ELSA-2026-79371)	Nessus	Oracle Linux Local Security Checks	Local	critical
364314	RHEL 10 : dovecot (RHSA-2026:79371)	Nessus	Red Hat Local Security Checks	Local	critical
364192	Rocky Linux 8 [CIQ] Security Update: dovecot / dovecot-debuginfo / dovecot-debugsource / dovecot-devel / etc Multiple Vulnerabilities (crlsa-2026_76763)	Nessus	Rocky Linux Local Security Checks	Local	critical
363927	AlmaLinux 8 : dovecot (ALSA-2026:76763)	Nessus	Alma Linux Local Security Checks	Local	critical
363755	Oracle Linux 8 : dovecot (ELSA-2026-76763)	Nessus	Oracle Linux Local Security Checks	Local	critical
363744	RockyLinux 8 : dovecot (RLSA-2026:76763)	Nessus	Rocky Linux Local Security Checks	Local	critical
363392	RHEL 8 : dovecot (RHSA-2026:76763)	Nessus	Red Hat Local Security Checks	Local	critical
350920	Debian dsa-6526 : dovecot-auth-lua - security update	Nessus	Debian Local Security Checks	Local	critical
342588	openSUSE 16: dovecot24 / dovecot24-backend-mysql / dovecot24-backend-pgsql / etc (openSUSE-SU-2026:21720-1)	Nessus	SuSE Local Security Checks	Local	critical
446515	Alpine: multiple dovecot packages: security update to 2.4.5-r0	Tenable Cloud Security	Alpine Linux Local Security Checks	Local	critical
446515	Alpine: multiple dovecot packages: security update to 2.4.5-r0	Tenable Self-Hosted Container Security	Alpine Linux Local Security Checks	Local	critical
341537	Linux Distros Unpatched Vulnerability : CVE-2026-73208	Nessus	Misc.	Local	high

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