CVE-2026-33263Network attack vector

Login-process crash via invalid epoll descriptor deletion

Published Aug 28, 2026 · Updated Aug 28, 2026

Denial of service in OX Dovecot CE and Pro submission-login allows remote authenticated users to crash login processes. When mail_max_userip_connections is reached, faulty file-descriptor handling calls epoll_ctl to delete an invalid descriptor and triggers a panic. Reaching the default limit of 10 concurrent per-user-IP connections is required; high-security mode drops the new connection, while high-performance mode terminates every connection in that process and can duplicate messages.

CVSS severity4.3
Medium
EPSS probability0.29%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in OX Dovecot CE and Pro submission-login allows remote authenticated users to crash login processes. When mail_max_userip_connections is reached, faulty file-descriptor handling calls epoll_ctl to delete an invalid descriptor and triggers a panic. Reaching the default limit of 10 concurrent per-user-IP connections is required; high-security mode drops the new connection, while high-performance mode terminates every connection in that process and can duplicate messages.

The record

CVE
CVE-2026-33263
Published
Aug 28, 2026
Updated
Aug 28, 2026
Vendor
Open-Xchange GmbH
Product
OX Dovecot CE
Classifications
CWE-403, T1499.004
Attack vector
network
Privileges
authenticated

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=2.3.0 <2.4.5

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Open-Xchange GmbH · OX Dovecot CEversion=2.3.0 <2.4.5
Open-Xchange GmbH · OX Dovecot Proversion=2.3.0 <2.3.22.2; version=3.0.0 <3.0.7; version=3.1.0 <3.1.6

Published CVSS scores

4.3Open-Xchange GmbHCVSS:3.1/AV:N/AC:L/PR:L/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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-403Exposure of File Descriptor to Unintended Control Sphere ('File Descriptor Leak')
T1499.004Application or System Exploitation

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

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Your stack

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