Dovecot SQL based authentication can be bypassed when auth_username_chars is cleared by admin. This vulnerability allows bypassing authentication for any user and user enumeration. Do not clear auth_username_chars. If this is not possible, install latest fixed version. No publicly available exploits are known.

The remote openSUSE 16 host has packages installed that are affected by multiple vulnerabilities as referenced in the openSUSE-SU-2026:20554-1 advisory.

    - Update to v2.4.3
    - CVE-2025-59028: Invalid base64 authentication can cause DoS for other logins (bsc#1260894).
    - CVE-2025-59031: decode2text.sh OOXML extraction may follow symlinks and read unintended files during     indexing       (bsc#1260895).
    - CVE-2025-59032: pigeonhole: ManageSieve panic occurs with sieve-connect as a client (bsc#1260902).
    - CVE-2026-24031: SQL injection possible if auth_username_chars is configured empty. Fixed escaping to     always happen.
      v2.4 regression (bsc#1260896).
    - CVE-2026-27855: OTP driver vulnerable to replay attack (bsc#1260900).
    - CVE-2026-27856: Doveadm credentials were not checked using timing-safe checking function (bsc#1260899).
    - CVE-2026-27857: sending excessive parenthesis causes imap-login to use excessive memory (bsc#1260898).
    - CVE-2026-27858: pigeonhole: managesieve-login can allocate large amount of memory during authentication     (bsc#1260901).
    - CVE-2026-27859: excessive RFC 2231 MIME parameters in email would can excessive CPU usage (bsc#1260897).
    - CVE-2026-27860: LDAP query injection possible if auth_username_chars is configured empty. Fixed escaping     to always       happen. v2.4 regression (bsc#1260893).

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 SUSE Linux SLES16 / SLES_SAP16 host has packages installed that are affected by multiple vulnerabilities as referenced in the SUSE-SU-2026:21208-1 advisory.

    - Update to v2.4.3
    - CVE-2025-59028: Invalid base64 authentication can cause DoS for other logins (bsc#1260894).
    - CVE-2025-59031: decode2text.sh OOXML extraction may follow symlinks and read unintended files during     indexing       (bsc#1260895).
    - CVE-2025-59032: pigeonhole: ManageSieve panic occurs with sieve-connect as a client (bsc#1260902).
    - CVE-2026-24031: SQL injection possible if auth_username_chars is configured empty. Fixed escaping to     always happen.
      v2.4 regression (bsc#1260896).
    - CVE-2026-27855: OTP driver vulnerable to replay attack (bsc#1260900).
    - CVE-2026-27856: Doveadm credentials were not checked using timing-safe checking function (bsc#1260899).
    - CVE-2026-27857: sending excessive parenthesis causes imap-login to use excessive memory (bsc#1260898).
    - CVE-2026-27858: pigeonhole: managesieve-login can allocate large amount of memory during authentication     (bsc#1260901).
    - CVE-2026-27859: excessive RFC 2231 MIME parameters in email would can excessive CPU usage (bsc#1260897).
    - CVE-2026-27860: LDAP query injection possible if auth_username_chars is configured empty. Fixed escaping     to always       happen. v2.4 regression (bsc#1260893).

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 Debian 12 host has packages installed that are affected by multiple vulnerabilities as referenced in the dsa-6197 advisory.

    - -------------------------------------------------------------------------     Debian Security Advisory DSA-6197-1                   security@debian.org     https://www.debian.org/security/                       Moritz Muehlenhoff     April 05, 2026                        https://www.debian.org/security/faq
    - -------------------------------------------------------------------------

    Package        : dovecot     CVE ID         : CVE-2025-59031 CVE-2025-59032 CVE-2026-27855                      CVE-2026-27856 CVE-2026-27857 CVE-2026-27858                      CVE-2026-27859 CVE-2026-59028 CVE-2026-24031                      CVE-2026-27860 CVE-2026-0394

    Multiple vulnerabilities have been discovered in the Dovecot IMAP server     which way result in denial of service, SQL injection, path traversal,     replay attacks or timing side channel attacks.

    For the oldstable distribution (bookworm), these problems have been fixed     in version 1:2.3.19.1+dfsg1-2.1+deb12u2.

    For the stable distribution (trixie), these problems have been fixed in     version 1:2.4.1+dfsg1-6+deb13u4.

    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 Ubuntu 22.04 LTS / 24.04 LTS / 25.10 host has packages installed that are affected by multiple vulnerabilities as referenced in the USN-8136-1 advisory.

    It was discovered that Dovecot incorrectly handled invalid base64 SASL data. An attacker could possibly     use this issue to cause a denial of service. This issue only affected Ubuntu 25.10. (CVE-2025-59028)

    It was discovered that Dovecot script decode2text.sh incorrectly handled zip files. An attacker could     possibly use this issue to obtain sensitive information. (CVE-2025-59031)

    It was discovered that Dovecot incorrectly handled certain AUTHENTICATE requests. An attacker could     possibly use this issue to cause a denial of service. (CVE-2025-59032)

    It was discovered that Dovecot incorrectly handled certain SQL based authentication. An attacker could     possibly use this issue to bypass authentication. This issue only affected Ubuntu 25.10. (CVE-2026-24031)

    It was discovered that Dovecot incorrectly handled certain LDAP based authentication. An attacker could     possibly use this issue to bypass restrictions and allow probing of LDAP structure. This issue only     affected Ubuntu 25.10. (CVE-2026-27860)

    It was discovered that Dovecot is vulnerable to replay attack under certain conditions. An attacker could     possibly use this issue to bypass authentication. (CVE-2026-27855)

    It was discovered that Dovecot is vulnerable to a timing attack under certain conditions. An attacker     could possibly use this issue to bypass authentication. (CVE-2026-27856)

    It was discovered that Dovecot incorrectly handled certain IMAP login requests. An attacker could possibly     use this issue to cause a denial of service. (CVE-2026-27857)

    It was discovered that Dovecot incorrectly handled certain specially crafted messages. An attacker could     possibly use this issue to cause a denial of service. (CVE-2026-27858)

    It was discovered that Dovecot incorrectly handled certain specially crafted mail messages. An attacker     could possibly use this issue to cause a denial of service. (CVE-2026-27859)

    It was discovered that Dovecot incorrectly handles file paths. A attacker could possibly use this issue to     perform a path traversal and obtain or modify arbitrary files. This issue only affected Ubuntu 22.04 LTS     and Ubuntu 24.04 LTS. (CVE-2026-0394)

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.

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

  - Dovecot SQL based authentication can be bypassed when auth_username_chars is cleared by admin. This
    vulnerability allows bypassing authentication for any user and user enumeration. Do not clear
    auth_username_chars. If this is not possible, install latest fixed version. No publicly available exploits
    are known. (CVE-2026-24031)

  - When sending invalid base64 SASL data, login process is disconnected from the auth server, causing all
    active authentication sessions to fail. Invalid BASE64 data can be used to DoS a vulnerable server to
    break concurrent logins. Install fixed version or disable concurrency in login processes (heavy perfomance
    penalty on large deployments). No publicly available exploits are known. (CVE-2025-59028)

  - Dovecot has provided a script to use for attachment to text conversion. This script unsafely handles zip-
    style attachments. Attacker can use specially crafted OOXML documents to cause unintended files on the
    system to be indexed and subsequently ending up in FTS indexes. Do not use the provided script, instead,
    use something else like FTS tika. No publicly available exploits are known. (CVE-2025-59031)

  - Dovecot OTP authentication is vulnerable to replay attack under specific conditions. If auth cache is
    enabled, and username is altered in passdb, then OTP credentials can be cached so that same OTP reply is
    valid. An attacker able to observe an OTP exchange is able to log in as the user. If authentication
    happens over unsecure connection, switch to SCRAM protocol. Alternatively ensure the communcations are
    secured, and if possible switch to OAUTH2 or SCRAM. No publicly available exploits are known.
    (CVE-2026-27855)

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

  - Dovecot SQL based authentication can be bypassed when auth_username_chars is cleared by admin. This     vulnerability allows bypassing authentication for any user and user enumeration. Do not clear     auth_username_chars. If this is not possible, install latest fixed version. No publicly available exploits     are known. (CVE-2026-24031)

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

ID	Name	Product	Family	Severity
309138	openSUSE 16 Security Update : dovecot24 (openSUSE-SU-2026:20554-1)	Nessus	SuSE Local Security Checks	high
309128	SUSE SLES16 Security Update : dovecot24 (SUSE-SU-2026:21208-1)	Nessus	SuSE Local Security Checks	high
305037	Debian dsa-6197 : dovecot-auth-lua - security update	Nessus	Debian Local Security Checks	high
304437	Ubuntu 22.04 LTS / 24.04 LTS / 25.10 : Dovecot vulnerabilities (USN-8136-1)	Nessus	Ubuntu Local Security Checks	high
439446	Alpine: multiple dovecot packages: security update to 2.4.3-r0	Tenable Cloud Security	Alpine Linux Local Security Checks	high
439446	Alpine: multiple dovecot packages: security update to 2.4.3-r0	Tenable Self-Hosted Container Security	Alpine Linux Local Security Checks	high
304090	Linux Distros Unpatched Vulnerability : CVE-2026-24031	Nessus	Misc.	high

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CVE-2026-24031

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