CVE-2026-40019Network attack vector

Unauthenticated CPU exhaustion via truncated quoted argument

Published Aug 28, 2026 · Updated Aug 28, 2026

Uncontrolled resource consumption in OX Dovecot CE 2.4.3 through 2.4.4 allows remote attackers to exhaust server CPU via ManageSieve. The pre-authentication managesieve-login parser fails to advance past a truncated quoted argument and loops indefinitely on the same input while consuming CPU. ManageSieve must be enabled and reachable; repeated unauthenticated connections can consume all server CPU and deny Sieve script management.

CVSS severity5.9
Medium
EPSS probability0.32%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Uncontrolled resource consumption in OX Dovecot CE 2.4.3 through 2.4.4 allows remote attackers to exhaust server CPU via ManageSieve. The pre-authentication managesieve-login parser fails to advance past a truncated quoted argument and loops indefinitely on the same input while consuming CPU. ManageSieve must be enabled and reachable; repeated unauthenticated connections can consume all server CPU and deny Sieve script management.

The record

CVE
CVE-2026-40019
Published
Aug 28, 2026
Updated
Aug 28, 2026
Vendor
Open-Xchange GmbH
Product
OX Dovecot CE
Classifications
CWE-400, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 28, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 28, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=2.4.3 <2.4.5

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Open-Xchange GmbH · OX Dovecot CEversion=2.4.3 <2.4.5

Published CVSS scores

5.9Open-XchangeCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-400Uncontrolled Resource Consumption
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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