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Full vulnerability report · 2026
CVE-2026-42391High confidence

An unauthenticated attacker can send an IMAP ID command with a very large number of parameters before logging in, which causes memory and CPU usage to grow disproportionately

Open-Xchange GmbH · OX Dovecot Pro

7.5HighCVSS 3.1
Recommended action
Within 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

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 releaseSource packageVendor stateFixed versionEvidence
Ubuntu 24.04 LTSnoble · standard archivedovecotUnder evaluationCanonical reports that the package might be affected and still needs evaluation or fixing.Not published in this feedCanonical 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-2026-42391 · CSAF 2.0 · revision 3 · finalRed Hat Product Securitydovecot: Dovecot: Denial of Service via IMAP ID command with excessive parameters
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 Dovecot. An unauthenticated attacker can send an IMAP ID command with a very large number of parameters before logging in. This action causes the server to consume excessive memory and CPU resources, leading to the termination of login processes and other active connections. This can result in a degradation or complete denial of service for IMAP logins.
Remediation
To mitigate this issue, limit the number of connections handled by a single `imap-login` process by adjusting the `process_limit` setting within the `service imap-login` block in your Dovecot configuration (e.g., `/etc/dovecot/dovecot.conf`). Increasing `process_limit` will cause Dovecot to spawn more `imap-login` processes, distributing connections more widely and reducing the impact of a single malicious connection. For example, to set the process limit to 200: ``` # /etc/dovecot/dovecot.conf service imap-login { process_limit = 200 } ``` After modifying the configuration, restart the Dovecot service for the changes to take effect. This may impact performance due to increased process overhead. ```bash systemctl restart dovecot ```
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Select the national-authority views to include. The exact source language is shown on each matched advisory. Your choice is remembered on this device and encoded in the shareable URL.

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-2026-67674

No EUVD known-exploited evidence

An unauthenticated attacker can send an IMAP ID command with a very large number of parameters before logging in, which causes memory and CPU usage to grow disproportionately. The login process can be terminated by the out-of-memory handling, which also terminates all other connections handled by the same process. This can cause degradation or denial of service for IMAP logins. Limit the number of connections handled by a single imap-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
7.5 · CVSS 3.1
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Mitigation available
01

What, why and how

An unauthenticated attacker can send an IMAP ID command with a very large number of parameters before logging in, which causes memory and CPU usage to grow disproportionately. The login process can be terminated by the out-of-memory handling, which also terminates all other connections handled by the same process. This can cause degradation or denial of service for IMAP logins. Limit the number of connections handled by a single imap-login process. This has a performance impact though. Update to non-vulnerable version. No publicly available exploits are known.

What

An unauthenticated attacker can send an IMAP ID command with a very large number of parameters before logging in, which causes memory and CPU usage to grow disproportionately. The login process can be terminated by the out-of-memory handling, which also terminates all other connections handled by the same process. This can cause degradation or denial of service for IMAP logins. Limit the number of connections handled by a single imap-login process. This has a performance impact though. Update to non-vulnerable version. No publicly available exploits are known.

Why

The product does not properly control the allocation and maintenance of a limited resource.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may disrupt the affected service.

What

An unauthenticated attacker can send an IMAP ID command with a very large number of parameters before logging in, which causes memory and CPU usage to grow disproportionately. The login process can be terminated by the out-of-memory handling, which also terminates all other connections handled by the same process. This can cause degradation or denial of service for IMAP logins. Limit the number of connections handled by a single imap-login process. This has a performance impact though. Update to non-vulnerable version. No publicly available exploits are known.

Why

The product does not properly control the allocation and maintenance of a limited resource.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may disrupt the affected service.

02

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 → Uncontrolled Resource Consumption → disrupt the affected service
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
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-400 ↗

CWE-400: Uncontrolled Resource Consumption. The product does not properly control the allocation and maintenance of a limited resource.

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:N/UI:N/S:U/C:N/I:N/A:H

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.PRNonePrivileges required: The attacker does not need an account or existing 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.AHighAvailability impact: A successful attack can cause a major 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.
NetworkUnauthenticatedDenial of serviceCWE-400
A

Official authority intelligence

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

ENISA EUVD · EUVD-2026-67674Official EUVD mapping

An unauthenticated attacker can send an IMAP ID command with a very large number of parameters before logging in, which causes memory and CPU usage to grow disproportionately. The login process can be terminated by the out-of-memory handling, which also terminates all other connections handled by the same process. This can cause degradation or denial of service for IMAP logins. Limit the number of connections handled by a single imap-login process. This has a performance impact though. Update to non-vulnerable version. No publicly available exploits are known.

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
03

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 `imap-login` process by adjusting the `process_limit` setting within the `service imap-login` block in your Dovecot configuration (e.g., `/etc/dovecot/dovecot.conf`). Increasing `process_limit` will cause Dovecot to spawn more `imap-login` processes, distributing connections more widely and reducing the impact of a single malicious connection. For example, to set the process limit to 200: ``` # /etc/dovecot/dovecot.conf service imap-login { process_limit = 200 } ``` After modifying the configuration, restart the Dovecot service for the changes to take effect. This may impact performance due to increased process overhead. ```bash systemctl restart dovecot ```
04

Evidence and provenance

Published 28 Aug 2026 · Last source change 28 Aug 2026, 15:54 UTC · CWE-400 · Uncontrolled Resource Consumption

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-2026-67674
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 →
  1. ENISA EUVD mappingEUVD-2026-67674 was added to the official ENISA EUVD mapping for this CVE.
    Before
    not recorded
    After
    {"euvdId":"EUVD-2026-67674"}
    ENISA EUVD ↗
  2. Catalogue recordCVE added to the BlackTree catalogue.
    CNA ↗
Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
ENISA EUVD · EUVD-2026-67674↗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.
Free version - for non-commercial use only.CVE-2026-42391 · cve.blacktree.nl