An attacker that can send mail to a user can craft a message header whose values are chosen to collide in an internal hash table, which makes the IMAP THREAD command consume CPU disproportionate to the size of the message. This is a separate issue from CVE-2026-40014 and is not addressed by that fix. Whenever a mail client issues a THREAD command on the affected mailbox, this can cause degradation or denial of service for IMAP. Monitor system for abnormal CPU usage, kill the offending process and remove the offending message from the affected mailbox. Update to non-vulnerable version. No publicly available exploits are known.

The remote Fedora 45 host has a package installed that is affected by multiple vulnerabilities as referenced in the FEDORA-2026-8b8efbd2b8 advisory.

    - updated to 2.4.5, many security fixes

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 Fedora 44 host has a package installed that is affected by multiple vulnerabilities as referenced in the FEDORA-2026-2e6b786570 advisory.

    - updated to 2.4.5, many security fixes

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 Fedora 43 host has a package installed that is affected by multiple vulnerabilities as referenced in the FEDORA-2026-e8a6485109 advisory.

    - updated to 2.4.5, many security fixes

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 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 can send mail to a user can craft a message header whose values are chosen to collide in     an internal hash table, which makes the IMAP THREAD command consume CPU disproportionate to the size of     the message. This is a separate issue from CVE-2026-40014 and is not addressed by that fix. Whenever a     mail client issues a THREAD command on the affected mailbox, this can cause degradation or denial of     service for IMAP. Monitor system for abnormal CPU usage, kill the offending process and remove the     offending message from the affected mailbox. Update to non-vulnerable version. No publicly available     exploits are known. (CVE-2026-40017)

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

ID	Name	Product	Family	Type	Severity
348271	Fedora 45 : dovecot (2026-8b8efbd2b8)	Nessus	Fedora Local Security Checks	Local	critical
348254	Fedora 44 : dovecot (2026-2e6b786570)	Nessus	Fedora Local Security Checks	Local	critical
348253	Fedora 43 : dovecot (2026-e8a6485109)	Nessus	Fedora 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
341525	Linux Distros Unpatched Vulnerability : CVE-2026-40017	Nessus	Misc.	Local	medium

Detections

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CVE-2026-40017

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