BlackTreeIndependent security intelligence

Full vulnerability report · 2026

CVE-2026-33263High confidence

Update to non-vulnerable version

Open-Xchange GmbH · OX Dovecot Pro

4.3MediumCVSS 3.1

Recommended action

Scheduled

Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority.

Mitigation available

Distribution package intelligence

Ubuntu vendor package status

Canonical’s release and source-package findings are shown separately from local repository availability.

1 package state

Repository candidate not checked

A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.

Ubuntu release	Source package	Vendor state	Fixed version	Evidence
Ubuntu 24.04 LTSnoble · standard archive	`dovecot`	Under evaluationCanonical reports that the package might be affected and still needs evaluation or fixing.	`Not published in this feed`	Canonical record ↗Source updated 8 Sept 2026

Direct vendor intelligence

Authoritative vendor CSAF and VEX advisories

Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.

1 current

CVE-2026-33263 · CSAF 2.0 · revision 3 · finalRed Hat Product Securitydovecot: Dovecot: Denial of Service and potential message duplication via connection limit exhaustion

30 known affected

The vendor explicitly identifies these products as affected by this CVE.

dovecot as a component of Red Hat Enterprise Linux 10
dovecot-devel as a component of Red Hat Enterprise Linux 10
dovecot-mysql as a component of Red Hat Enterprise Linux 10
dovecot-pgsql as a component of Red Hat Enterprise Linux 10
dovecot-pigeonhole as a component of Red Hat Enterprise Linux 10
dovecot.src as a component of Red Hat Enterprise Linux 10
dovecot as a component of Red Hat Enterprise Linux 6
dovecot-devel as a component of Red Hat Enterprise Linux 6
dovecot-mysql as a component of Red Hat Enterprise Linux 6
dovecot-pgsql as a component of Red Hat Enterprise Linux 6
dovecot-pigeonhole as a component of Red Hat Enterprise Linux 6
dovecot.src as a component of Red Hat Enterprise Linux 6

Summary: A flaw was found in the Dovecot mail server's `submission-login` component. This vulnerability occurs when the server reaches its maximum allowed user IP connections, leading to a crash due to file descriptor handling issues. This can result in a denial of service, preventing users from sending emails, and potentially causing duplicate message delivery under certain conditions.
Remediation: To mitigate this issue, limit the number of connections handled by a single submission-login process. This can be achieved by adjusting the `process_limit` setting for the `submission-login` service in the Dovecot configuration. For example, add or modify the following in a Dovecot configuration file (e.g., `/etc/dovecot/conf.d/10-master.conf`): ``` service submission-login { process_limit = } ``` Reducing this limit may impact performance. After modifying the configuration, restart the Dovecot service for the changes to take effect.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current

ENISA EUVD identifier

EUVD-2026-67658

No EUVD known-exploited evidence

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.

EUVD state: Present in the current official mapping
Known exploitation: Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score: 4.3 · CVSS 3.1
Advisory evidence: No linked advisory details stored yet

Recommended actionScheduled

Medium technical severity with no CISA KEV confirmation; remediate through the normal risk-based patch cycle unless local exposure raises the priority.

Mitigation available

What, why and how

What

Why

A process does not close sensitive file descriptors before invoking a child process, which allows the child to perform unauthorized I/O operations using those descriptors.

How

An attacker operating through a network path may attempt exploitation with low privileges. If successful, the issue may disrupt the affected service.

What

Why

A process does not close sensitive file descriptors before invoking a child process, which allows the child to perform unauthorized I/O operations using those descriptors.

How

An attacker operating through a network path may attempt exploitation with low privileges. If successful, the issue may disrupt the affected service.

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation

Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.

No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material

Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.

None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path: a network path → Exposure of File Descriptor to Unintended Control Sphere ('File Descriptor Leak') → disrupt the affected service
Attack surface: Network
Privileges required: Low: a basic authenticated account is required
User interaction: None
Attack complexity: Low: no specialised conditions are recorded
Security boundary: Unchanged: impact remains within the vulnerable component's security authority
Weakness ? CWE means Common Weakness Enumeration: a standard category for the underlying weakness.: CWE-403 ↗
CWE-403: Exposure of File Descriptor to Unintended Control Sphere ('File Descriptor Leak'). A process does not close sensitive file descriptors before invoking a child process, which allows the child to perform unauthorized I/O operations using those descriptors.
CVSS vector ? CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.
AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRLowPrivileges required: The attacker needs basic user-level privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CNoneConfidentiality impact: No direct loss is represented by this metric.INoneIntegrity impact: No direct loss is represented by this metric.ALowAvailability impact: A successful attack can cause a limited loss.
Post-exploitation / living off the land: No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.

NetworkDenial of serviceCWE-403

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

ENISA EUVD · EUVD-2026-67658Official EUVD mapping

Official EUVD record

BSI · German · WID-SEC-W-2026-3076Dovecot: Mehrere Schwachstellen

Ein Angreifer kann mehrere Schwachstellen in Dovecot ausnutzen, um Sicherheitsvorkehrungen zu umgehen, sensible Informationen offenzulegen, Daten zu manipulieren oder Denial-of-Service-Zustände herbeizuführen.

Official advisory

Patch and workaround

Operational remediation based on structured source evidence.

Status ? Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.: Mitigation available
Affected: dovecot as a component of Red Hat Enterprise Linux 10; dovecot-devel as a component of Red Hat Enterprise Linux 10; dovecot-mysql as a component of Red Hat Enterprise Linux 10; dovecot-pgsql as a component of Red Hat Enterprise Linux 10; dovecot-pigeonhole as a component of Red Hat Enterprise Linux 10; dovecot.src as a component of Red Hat Enterprise Linux 10; dovecot as a component of Red Hat Enterprise Linux 6; dovecot-devel as a component of Red Hat Enterprise Linux 6; dovecot-mysql as a component of Red Hat Enterprise Linux 6; dovecot-pgsql as a component of Red Hat Enterprise Linux 6; dovecot-pigeonhole as a component of Red Hat Enterprise Linux 6; dovecot.src as a component of Red Hat Enterprise Linux 6; dovecot as a component of Red Hat Enterprise Linux 7; dovecot-devel as a component of Red Hat Enterprise Linux 7; dovecot-mysql as a component of Red Hat Enterprise Linux 7; dovecot-pgsql as a component of Red Hat Enterprise Linux 7; dovecot-pigeonhole as a component of Red Hat Enterprise Linux 7; dovecot.src as a component of Red Hat Enterprise Linux 7; dovecot as a component of Red Hat Enterprise Linux 8; dovecot-devel as a component of Red Hat Enterprise Linux 8; dovecot-mysql as a component of Red Hat Enterprise Linux 8; dovecot-pgsql as a component of Red Hat Enterprise Linux 8; dovecot-pigeonhole as a component of Red Hat Enterprise Linux 8; dovecot.src as a component of Red Hat Enterprise Linux 8; dovecot as a component of Red Hat Enterprise Linux 9; dovecot-devel as a component of Red Hat Enterprise Linux 9; dovecot-mysql as a component of Red Hat Enterprise Linux 9; dovecot-pgsql as a component of Red Hat Enterprise Linux 9; dovecot-pigeonhole as a component of Red Hat Enterprise Linux 9; dovecot.src as a component of Red Hat Enterprise Linux 9
Fixed: No fixed version is explicitly recorded in the structured CVE data.
Action: No verified patch reference is present in the current structured sources. Check the vendor advisory before making a change.
Workaround: To mitigate this issue, limit the number of connections handled by a single submission-login process. This can be achieved by adjusting the `process_limit` setting for the `submission-login` service in the Dovecot configuration. For example, add or modify the following in a Dovecot configuration file (e.g., `/etc/dovecot/conf.d/10-master.conf`): ``` service submission-login { process_limit = } ``` Reducing this limit may impact performance. After modifying the configuration, restart the Dovecot service for the changes to take effect.

Evidence and provenance

Published 28 Aug 2026 · Last source change 28 Aug 2026, 15:55 UTC · CWE-403 · Exposure of File Descriptor to Unintended Control Sphere ('File Descriptor Leak')

CVE recordCVE.org · 5.2

CVSS sourceCNA

EPSS source

The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.

FIRST · tracked since 2026-08-29

European sourceENISA EUVD · EUVD-2026-67658

Product sourceVendor CSAF · Red Hat Product Security

Remediation sourceVendor CSAF · Red Hat Product Security

CWE sourceCNA

NVD statusNVD not scheduled

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates →

28 Aug 2026, 14:12 UTC
ENISA EUVD mappingEUVD-2026-67658 was added to the official ENISA EUVD mapping for this CVE.
Before
not recorded
After
{"euvdId":"EUVD-2026-67658"}
ENISA EUVD ↗
28 Aug 2026, 10:30 UTC
Catalogue recordCVE added to the BlackTree catalogue.
CNA ↗

2026-08-28CVE published

ENISA EUVD · EUVD-2026-67658↗Vendor CSAF · Red Hat Product Security↗CVE authority or vendor reference↗Official CVE record (CNA and ADP data)↗NVD record↗

Technical terms and abbreviations used in this report

CVE: Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS: Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS: Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE: Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA: CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP: Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD: National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT: A computer security incident response team that publishes warnings or coordinates incident response.
PoC: Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF: Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL: Living off the land: abuse of legitimate tools or system functions during an attack.