CVE-2026-27859Network attack vector

Mail-delivery CPU exhaustion via excessive MIME parameters

Published Mar 27, 2026 · Updated Mar 27, 2026

Denial of service in Open-Xchange Dovecot Pro 2.4.0, 3.0.2, and 3.1.0 and earlier allows remote attackers to consume LMTP CPU. The message-header MIME parser performs excessive processing when a delivered message contains an excessive number of RFC 2231 parameters. No authentication or user interaction is required; delivery of a crafted message can monopolize the mail-delivery process without a reported crash.

CVSS severity5.3
Medium
EPSS probability0.37%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Denial of service in Open-Xchange Dovecot Pro 2.4.0, 3.0.2, and 3.1.0 and earlier allows remote attackers to consume LMTP CPU. The message-header MIME parser performs excessive processing when a delivered message contains an excessive number of RFC 2231 parameters. No authentication or user interaction is required; delivery of a crafted message can monopolize the mail-delivery process without a reported crash.

The record

CVE
CVE-2026-27859
Published
Mar 27, 2026
Updated
Mar 27, 2026
Vendor
Open-Xchange GmbH
Product
Dovecot Pro
Classifications
CWE-400, T1499.003
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 27, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 27, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=0 <=2.4.0
  2. Affected versionversion=0 <=3.0.2
  3. Affected versionversion=0 <=3.1.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Open-Xchange GmbH · Dovecot Proversion=0 <=2.4.0; version=0 <=3.0.2; version=0 <=3.1.0

Published CVSS scores

5.3Open-XchangeCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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
T1499.003Application Exhaustion Flood

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo