CVE-2026-27858Network attack vector

Pre-auth service crashes via unbounded memory allocation

Published Mar 27, 2026 · Updated Mar 27, 2026

Resource exhaustion in ManageSieve in Open-Xchange Dovecot Pro 3.1.0 and earlier allows remote attackers to crash the login service. Open-Xchange identifies managesieve-login as the allocation locus but has not disclosed the crafted pre-authentication message field or parser operation that permits unbounded memory growth. Repeated messages exhaust process memory and terminate managesieve-login without credentials, interrupting access to the ManageSieve service.

CVSS severity7.5
High
EPSS probability0.79%
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

Resource exhaustion in ManageSieve in Open-Xchange Dovecot Pro 3.1.0 and earlier allows remote attackers to crash the login service. Open-Xchange identifies managesieve-login as the allocation locus but has not disclosed the crafted pre-authentication message field or parser operation that permits unbounded memory growth. Repeated messages exhaust process memory and terminate managesieve-login without credentials, interrupting access to the ManageSieve service.

The record

CVE
CVE-2026-27858
Published
Mar 27, 2026
Updated
Mar 27, 2026
Vendor
Open-Xchange GmbH
Product
Dovecot Pro
Classifications
CWE-400, T1499
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 <=2.3.0
  2. Affected versionversion=0 <=2.4.0
  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 <=2.3.0; version=0 <=2.4.0; version=0 <=3.1.0

Published CVSS scores

7.5Open-Xchange GmbHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
8.7SUSECVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
7.5SUSECVSS:3.1/AV:N/AC:L/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.

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
T1499Endpoint Denial of Service

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