Critical Denial of Service Vulnerability in Dovecot IMAP Server
Summary
ALSA-2026:41905: Important: dovecot security update. Affects dovecot versions < 1:2.3.16-18.el9_8.1. Fixed in 1:2.3.16-18.el9_8.1. How to fix ↓
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Background
Dovecot is a widely used IMAP server designed for Linux and UNIX-like systems, emphasizing security and performance. It also includes a POP3 server and supports various email formats, including maildir and mbox. The software is modular, allowing for SQL drivers and authentication plugins as subpackages, making it a versatile choice for email management. However, it has recently been identified as vulnerable to a Denial of Service (DoS) attack due to excessive IMAP bracing, which can disrupt service availability.
Vulnerability Detail
The vulnerability, identified as CVE-2026-42006, allows attackers to exploit excessive IMAP bracing, leading to a Denial of Service condition. This can result in the server becoming unresponsive, affecting all users and potentially leading to data loss or service downtime. The issue arises from improper handling of specific IMAP commands, which can be triggered by maliciously crafted requests.
How To Fix
Minimum fixed version
1:2.3.16-18.el9_8.1
This is the first release that contains the fix.
sudo dnf update dovecotTip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
As a temporary workaround, you can limit access to the Dovecot server by implementing firewall rules to restrict connections from untrusted IP addresses. This will help mitigate the risk of exploitation until the package is updated.
Conclusion
The identified Denial of Service vulnerability in Dovecot (CVE-2026-42006) poses significant risks to server availability. It is essential for users to update to the patched version to safeguard their systems. Implementing temporary workarounds can help mitigate risks until the update is applied.
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FAQ
Dovecot is an open-source IMAP and POP3 server for Unix-like operating systems, designed with a focus on security and performance.
CVE-2026-42006 refers to a specific vulnerability in Dovecot that allows for Denial of Service attacks via excessive IMAP bracing.
You can use the Vulert playground at Vulert Scanner to check if your application is affected by this vulnerability without needing to sign up.
Failure to address this vulnerability may result in service disruptions, unavailability for users, and potential data loss.
It is recommended to regularly check for updates and apply them promptly to ensure your installation remains secure against known vulnerabilities.
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