CVE-2026-27852

Deferred Deferred - Pending Action

Memory Exhaustion in Open-Xchange Mail Server

Publication date: 2026-08-28

Last updated on: 2026-09-03

Assigner: Open-Xchange

Description

An attacker that can send mail to a user can craft a message whose headers contain a very large number of email addresses or MIME parameters, which causes excessive memory usage when the message is later parsed. The message is still delivered, but reading it over IMAP can exhaust the memory limit of the process and terminate it, causing denial of service for the affected user. Update to non-vulnerable version. No publicly available exploits are known.

CVSS Scores

EPSS Scores

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Meta Information

Published

2026-08-28

Last Modified

2026-09-03

Generated

2026-09-17

AI Q&A

2026-08-28

EPSS Evaluated

2026-09-15

NVD

CVE-2026-27852

EUVD

EUVD-2026-67657

Affected Vendors & Products

Vendor	Product	Version / Range
open-xchange	open-xchange	*

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-400	The product does not properly control the allocation and maintenance of a limited resource.

Attack-Flow Graph

Executive Summary

This vulnerability involves an attacker sending a specially crafted email with an excessive number of email addresses or MIME parameters in the headers. When the email is later parsed, it causes high memory usage. If the user tries to read this email via IMAP, the process may exceed its memory limit and crash, leading to a denial of service for that user.

Detection Guidance

This vulnerability is related to excessive memory usage when parsing email headers with large numbers of addresses or MIME parameters. Detection would require monitoring for abnormal memory consumption during IMAP operations or unusual email header sizes. Check IMAP server logs for processes terminating unexpectedly due to memory limits.

Impact Analysis

If you receive the malicious email, your email client or server may crash when processing it, preventing you from accessing your emails via IMAP. This disrupts your ability to read or manage emails until the issue is resolved.

Compliance Impact

This vulnerability primarily causes denial of service by exhausting memory during IMAP operations, which may disrupt email access for affected users. It does not directly impact data confidentiality or integrity, so its impact on GDPR or HIPAA compliance is likely minimal unless email service disruption leads to secondary compliance issues.

Mitigation Strategies

Update to a non-vulnerable version of Open-Xchange as specified in the CVE description. Implement rate limiting for email submissions to prevent excessive header sizes. Monitor IMAP server memory usage and set appropriate limits to prevent process termination.

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