CVE-2026-27856

Modified Modified - Updated After Analysis

Timing Oracle Vulnerability in Doveadm Enables Credential Disclosure

Publication date: 2026-03-27

Last updated on: 2026-06-30

Assigner: Open-Xchange

Description

Doveadm credentials are verified using direct comparison which is susceptible to timing oracle attack. An attacker can use this to determine the configured credentials. Figuring out the credential will lead into full access to the affected component. Limit access to the doveadm http service port, install fixed version. No publicly available exploits are known.

CVSS Scores

EPSS Scores

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Meta Information

Published

2026-03-27

Last Modified

2026-06-30

Generated

2026-07-06

AI Q&A

2026-03-27

EPSS Evaluated

2026-07-05

NVD

CVE-2026-27856

EUVD

EUVD-2026-16565

Affected Vendors & Products

Vendor	Product	Version / Range
dovecot	dovecot	to 2.4.3 (exc)
open-xchange	dovecot	From 3.0.0 (inc) to 3.0.5 (exc)
open-xchange	dovecot	From 3.1.0 (inc) to 3.1.4 (exc)
open-xchange	dovecot	to 2.3.22.1 (exc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-208	Two separate operations in a product require different amounts of time to complete, in a way that is observable to an actor and reveals security-relevant information about the state of the product, such as whether a particular operation was successful or not.
CWE-287	When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.

Attack-Flow Graph

Executive Summary

This vulnerability involves the Doveadm component verifying credentials using a direct comparison method that is vulnerable to a timing oracle attack.

An attacker can exploit this timing difference to determine the configured credentials.

Once the attacker figures out the credentials, they can gain full access to the affected component.

Impact Analysis

If exploited, this vulnerability can allow an attacker to obtain the credentials for the Doveadm component.

With these credentials, the attacker can gain full access to the affected component, potentially compromising the system.

This could lead to unauthorized access and control over the services provided by Doveadm.

Detection Guidance

This vulnerability involves a timing oracle attack on doveadm credentials due to direct comparison verification. Detection would involve monitoring access attempts to the doveadm HTTP service port and analyzing for unusual timing patterns or repeated authentication attempts that could indicate exploitation attempts.

Since no publicly available exploits are known and no specific detection commands are provided, general network monitoring and logging of access to the doveadm HTTP service port is recommended.

Mitigation Strategies

Limit access to the doveadm HTTP service port to trusted hosts only.
Install the fixed version of the software that addresses this vulnerability.

Compliance Impact

The vulnerability allows an attacker to determine configured credentials through a timing oracle attack, potentially leading to full access to the affected component. This unauthorized access could result in exposure or compromise of sensitive data.

Such unauthorized access and potential data compromise may negatively impact compliance with standards and regulations like GDPR and HIPAA, which require protection of personal and sensitive information.

Mitigation steps include limiting access to the doveadm HTTP service port and installing a fixed version, which are necessary to maintain compliance and reduce risk.

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