Attacker can upload a malicious Sieve script over ManageSieve service (or locally) to bypass configured CPU time limits for Sieve up to 130 times of the configured limit. Attacker can use this to degrade server performance and bypass configured CPU time limits for Sieve scripts. Install fixed version, or alternatively prevent direct access to Sieve scripts via ManageSieve or local access. No publicly available exploits are known.

The AlmaLinux 9.2 host has packages installed that are affected by multiple vulnerabilities as referenced in the TuxCare ALMALINUX9.2:CLSA-2026:1780910915 advisory.

  - Attacker can upload a malicious Sieve script over ManageSieve service (or locally) to bypass configured     CPU time limits for Sieve up to 130 times of the configured limit. Attacker can use this to degrade server     performance and bypass configured CPU time limits for Sieve scripts. Install fixed version, or     alternatively prevent direct access to Sieve scripts via ManageSieve or local access. No publicly     available exploits are known. (CVE-2026-40016)

  - Attacker can use the IMAP SETACL command to inject the anyone permission to user's dovecot-acl file even     if imap_acl_allow_anyone=no. This causes folders to be spammed to all users. The impact is limited to     being able to spam folders to other users, no unexpected access is gained. Install to fixed version. No     publicly available exploits are known. (CVE-2026-40020)

  - An attacker can cause uncontrolled memory usage with excessive bracing over IMAP. The fix in     CVE-2026-27857 was incomplete, only blocking one way of doing this, so there was still another way left     open. In particular, the fix was for closing braces, but you could still use open braces to bypass the     limit. Using excessive bracing, attacker can cause memory usage up to configured memory limit. Install     fixed version, or configure vsz_limit for imap process to low value. No publicly available exploits are     known. (CVE-2026-42006)

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 9.6 host has packages installed that are affected by multiple vulnerabilities as referenced in the TuxCare ALMALINUX9.6:CLSA-2026:1781096989 advisory.

  - Attacker can use a specially crafted base64 exchange between Dovecot and Client to fake SCRAM TLS channel     binding. This requires that the attacker is able to position itself between Dovecot and the client     connection. If successful, the attacker can eavesdrop communications between Dovecot and client as MITM     proxy. Install fixed version. No publicly available exploits are known. (CVE-2026-33603)

  - Attacker can upload a malicious Sieve script over ManageSieve service (or locally) to bypass configured     CPU time limits for Sieve up to 130 times of the configured limit. Attacker can use this to degrade server     performance and bypass configured CPU time limits for Sieve scripts. Install fixed version, or     alternatively prevent direct access to Sieve scripts via ManageSieve or local access. No publicly     available exploits are known. (CVE-2026-40016)

  - Attacker can use the IMAP SETACL command to inject the anyone permission to user's dovecot-acl file even     if imap_acl_allow_anyone=no. This causes folders to be spammed to all users. The impact is limited to     being able to spam folders to other users, no unexpected access is gained. Install to fixed version. No     publicly available exploits are known. (CVE-2026-40020)

  - An attacker can cause uncontrolled memory usage with excessive bracing over IMAP. The fix in     CVE-2026-27857 was incomplete, only blocking one way of doing this, so there was still another way left     open. In particular, the fix was for closing braces, but you could still use open braces to bypass the     limit. Using excessive bracing, attacker can cause memory usage up to configured memory limit. Install     fixed version, or configure vsz_limit for imap process to low value. No publicly available exploits are     known. (CVE-2026-42006)

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

The AlmaLinux 9.6 host has packages installed that are affected by multiple vulnerabilities as referenced in the TuxCare ALMALINUX9.6:CLSA-2026:1781096989 advisory.

  - Attacker can use a specially crafted base64 exchange between Dovecot and Client to fake SCRAM TLS channel     binding. This requires that the attacker is able to position itself between Dovecot and the client     connection. If successful, the attacker can eavesdrop communications between Dovecot and client as MITM     proxy. Install fixed version. No publicly available exploits are known. (CVE-2026-33603)

  - Attacker can upload a malicious Sieve script over ManageSieve service (or locally) to bypass configured     CPU time limits for Sieve up to 130 times of the configured limit. Attacker can use this to degrade server     performance and bypass configured CPU time limits for Sieve scripts. Install fixed version, or     alternatively prevent direct access to Sieve scripts via ManageSieve or local access. No publicly     available exploits are known. (CVE-2026-40016)

  - Attacker can use the IMAP SETACL command to inject the anyone permission to user's dovecot-acl file even     if imap_acl_allow_anyone=no. This causes folders to be spammed to all users. The impact is limited to     being able to spam folders to other users, no unexpected access is gained. Install to fixed version. No     publicly available exploits are known. (CVE-2026-40020)

  - An attacker can cause uncontrolled memory usage with excessive bracing over IMAP. The fix in     CVE-2026-27857 was incomplete, only blocking one way of doing this, so there was still another way left     open. In particular, the fix was for closing braces, but you could still use open braces to bypass the     limit. Using excessive bracing, attacker can cause memory usage up to configured memory limit. Install     fixed version, or configure vsz_limit for imap process to low value. No publicly available exploits are     known. (CVE-2026-42006)

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

The remote SUSE Linux SLES12 / SLES_SAP12 host has packages installed that are affected by a vulnerability as referenced in the SUSE-SU-2026:4271-1 advisory.

    This update for dovecot22 fixes the following issue:

    - CVE-2026-40016: Sieve :contains/:matches O(NxM) substring match bypasses sieve_max_cpu_time limit     (bsc#1265148).

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

Note that Nessus has not tested for this issue 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:

  - When safe filter is used with variable expansion, all following pipelines on the same string are
    incorrectly interpreted as safe too, enabling unsafe data to be unescaped. This can enable SQL / LDAP
    injection attacks when used in authentication. Avoid using safe filter until on fixed version. No publicly
    available exploits are known. (CVE-2026-27851)

  - Attacker can use a specially crafted base64 exchange between Dovecot and Client to fake SCRAM TLS channel
    binding. This requires that the attacker is able to position itself between Dovecot and the client
    connection. If successful, the attacker can eavesdrop communications between Dovecot and client as MITM
    proxy. Install fixed version. No publicly available exploits are known. (CVE-2026-33603)

  - Attacker can upload a malicious Sieve script over ManageSieve service (or locally) to bypass configured
    CPU time limits for Sieve up to 130 times of the configured limit. Attacker can use this to degrade server
    performance and bypass configured CPU time limits for Sieve scripts. Install fixed version, or
    alternatively prevent direct access to Sieve scripts via ManageSieve or local access. No publicly
    available exploits are known. (CVE-2026-40016)

  - Attacker can use the IMAP SETACL command to inject the anyone permission to user's dovecot-acl file even
    if imap_acl_allow_anyone=no. This causes folders to be spammed to all users. The impact is limited to
    being able to spam folders to other users, no unexpected access is gained. Install to fixed version. No
    publicly available exploits are known. (CVE-2026-40020)

  - An attacker can cause uncontrolled memory usage with excessive bracing over IMAP. The fix in
    CVE-2026-27857 was incomplete, only blocking one way of doing this, so there was still another way left
    open. In particular, the fix was for closing braces, but you could still use open braces to bypass the
    limit. Using excessive bracing, attacker can cause memory usage up to configured memory limit. Install
    fixed version, or configure vsz_limit for imap process to low value. No publicly available exploits are
    known. (CVE-2026-42006)

The remote SUSE Linux SLES16 / SLES_SAP16 host has packages installed that are affected by multiple vulnerabilities as referenced in the SUSE-SU-2026:22185-1 advisory.

    This update for dovecot24 fixes the following issues

    - CVE-2026-27851: lib-var-expand: safe filter leaks to all following pipelines (bsc#1265146).
    - CVE-2026-33603: login: base64 input can contain tabs that bypass IPC protection (bsc#1265147).
    - CVE-2026-40016: Sieve: contains/: matches O(NxM) substring match bypasses sieve_max_cpu_time limit     (bsc#1265148).
    - CVE-2026-40020: IMAP folders can be shared-spammed to everyone (bsc#1265149).
    - CVE-2026-42006: imap-login: uncontrolled memory usage with excessive bracing over IMAP (bsc#1265150).

    Changes for dovecot24:

    - Update to 2.4.4

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.

The remote Ubuntu 22.04 LTS / 24.04 LTS / 25.10 / 26.04 LTS host has packages installed that are affected by multiple vulnerabilities as referenced in the USN-8365-1 advisory.

    It was discovered that Dovecot incorrectly treated some variable expansion pipelines as safe in     authentication filters. An attacker could possibly use this issue to perform SQL or LDAP injection     attacks. This issue only affected Ubuntu 25.10 and Ubuntu 26.04 LTS. (CVE-2026-27851)

    It was discovered that Dovecot incorrectly verified SCRAM TLS channel binding in certain base64 exchanges.
    A remote attacker could possibly use this issue to obtain sensitive information in a machine-in-the-middle     attack. (CVE-2026-33603)

    It was discovered that Dovecot incorrectly enforced Sieve script CPU limits. An attacker could possibly     use this issue to cause Dovecot to use excessive resources, leading to a denial of service.
    (CVE-2026-40016)

    It was discovered that Dovecot incorrectly handled certain IMAP SETACL commands. An attacker could     possibly use this issue to spam folders to other users. (CVE-2026-40020)

    It was discovered that Dovecot incorrectly handled excessive IMAP bracing. An attacker could possibly use     this issue to cause Dovecot to use excessive resources, leading to a denial of service. (CVE-2026-42006)

Tenable has extracted the preceding description block directly from the Ubuntu 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 Fedora 43 host has a package installed that is affected by multiple vulnerabilities as referenced in the FEDORA-2026-693373747f advisory.

    * CVE-2026-27851: lib-var-expand: Safe filter marks all following pipelines safe.
    * CVE-2026-33603: auth: CRAM-SHA-*-PLUS channel binding could be faked.
      MITM attacker with a certificate trusted by the client could have       bypassed the requirement for channel binding.
    * CVE-2026-40020: IMAP folders can be shared-spammed to everyone.
    * CVE-2026-42006: An attacker can cause uncontrolled memory usage with       excessive bracing over IMAP. The fix in CVE-2026-27857 was incomplete.
    * indexer-worker, quota-status, script-login, program-client-local: Root       privileges are now dropped permanently before serving requests.
    * indexer-worker: Default restart_request_count changed to 1 to work       correctly after permanent root privilege drop.
    * lmtp: Add back service_extra_groups=$SET:default_internal_group that was       incorrectly removed in v2.4.3.
    * master: inet_listener_reuse_port has been replaced by service_reuse_port.
      The new setting properly pre-creates all listener sockets at startup and       assigns one unique socket per process. Using this allows evenly distributing       incoming connections to login processes.


Tenable has extracted the preceding description block directly from the Fedora 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 12 / 13 host has packages installed that are affected by multiple vulnerabilities as referenced in the dsa-6313 advisory.

    - -------------------------------------------------------------------------     Debian Security Advisory DSA-6313-1                   security@debian.org     https://www.debian.org/security/                       Moritz Muehlenhoff     May 31, 2026                          https://www.debian.org/security/faq
    - -------------------------------------------------------------------------

    Package        : dovecot     CVE ID         : CVE-2026-33603 CVE-2026-40016 CVE-2026-40020                      CVE-2026-42006 CVE-2026-27851

    Multiple vulnerabilities have been discovered in the Dovecot IMAP server     which way result in denial of service, SQL injection or     man-in-the-midddle attacks

    For the oldstable distribution (bookworm), these problems have been fixed     in version 1:2.3.19.1+dfsg1-2.1+deb12u6.

    For the stable distribution (trixie), these problems have been fixed in     version 1:2.4.1+dfsg1-6+deb13u6.

    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 Fedora 44 host has a package installed that is affected by multiple vulnerabilities as referenced in the FEDORA-2026-96eeb03b88 advisory.

    * CVE-2026-27851: lib-var-expand: Safe filter marks all following pipelines safe.
    * CVE-2026-33603: auth: CRAM-SHA-*-PLUS channel binding could be faked.
      MITM attacker with a certificate trusted by the client could have       bypassed the requirement for channel binding.
    * CVE-2026-40020: IMAP folders can be shared-spammed to everyone.
    * CVE-2026-42006: An attacker can cause uncontrolled memory usage with       excessive bracing over IMAP. The fix in CVE-2026-27857 was incomplete.
    * indexer-worker, quota-status, script-login, program-client-local: Root       privileges are now dropped permanently before serving requests.
    * indexer-worker: Default restart_request_count changed to 1 to work       correctly after permanent root privilege drop.
    * lmtp: Add back service_extra_groups=$SET:default_internal_group that was       incorrectly removed in v2.4.3.
    * master: inet_listener_reuse_port has been replaced by service_reuse_port.
      The new setting properly pre-creates all listener sockets at startup and       assigns one unique socket per process. Using this allows evenly distributing       incoming connections to login processes.


Tenable has extracted the preceding description block directly from the Fedora 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 Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - Attacker can upload a malicious Sieve script over ManageSieve service (or locally) to bypass configured     CPU time limits for Sieve up to 130 times of the configured limit. Attacker can use this to degrade server     performance and bypass configured CPU time limits for Sieve scripts. Install fixed version, or     alternatively prevent direct access to Sieve scripts via ManageSieve or local access. No publicly     available exploits are known. (CVE-2026-40016)

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

ID	Name	Product	Family	Type	Severity
361499	AlmaLinux 9.2 [TuxCare] Security Update: dovecot / dovecot-devel / dovecot-mysql / dovecot-pgsql / etc Multiple Vulnerabilities (ALMALINUX9.2:CLSA-2026:1780910915)	Nessus	Alma Linux Local Security Checks	Local	medium
361423	Rocky Linux 9.6 [TuxCare] Security Update: dovecot / dovecot-devel / dovecot-mysql / dovecot-pgsql / etc Multiple Vulnerabilities (ALMALINUX9.6:CLSA-2026:1781096989)	Nessus	Rocky Linux Local Security Checks	Local	medium
361415	AlmaLinux 9.6 [TuxCare] Security Update: dovecot / dovecot-devel / dovecot-mysql / dovecot-pgsql / etc Multiple Vulnerabilities (ALMALINUX9.6:CLSA-2026:1781096989)	Nessus	Alma Linux Local Security Checks	Local	medium
348726	SUSE SLES12: dovecot22 / dovecot22-backend-mysql / dovecot22-backend-pgsql / etc (SUSE-SU-2026:4271-1)	Nessus	SuSE Local Security Checks	Local	medium
445579	Alpine: multiple dovecot packages: security update to 2.4.4-r0	Tenable Cloud Security	Alpine Linux Local Security Checks	Local	critical
445579	Alpine: multiple dovecot packages: security update to 2.4.4-r0	Tenable Self-Hosted Container Security	Alpine Linux Local Security Checks	Local	critical
323080	SUSE SLES16: dovecot24 / dovecot24-backend-mysql / dovecot24-backend-pgsql / etc (SUSE-SU-2026:22185-1)	Nessus	SuSE Local Security Checks	Local	critical
318619	Ubuntu 22.04 LTS / 24.04 LTS / 25.10 / 26.04 LTS : Dovecot vulnerabilities (USN-8365-1)	Nessus	Ubuntu Local Security Checks	Local	critical
318284	Fedora 43 : dovecot (2026-693373747f)	Nessus	Fedora Local Security Checks	Local	critical
318247	Debian dsa-6313 : dovecot-auth-lua - security update	Nessus	Debian Local Security Checks	Local	critical
318245	Fedora 44 : dovecot (2026-96eeb03b88)	Nessus	Fedora Local Security Checks	Local	critical
315701	Linux Distros Unpatched Vulnerability : CVE-2026-40016	Nessus	Misc.	Local	medium

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