Critical Security Flaw in Dovecot IMAP Server: Multiple Vulnerabilities Addressed
Summary
ALSA-2026:79371: Important: dovecot security update. Affects dovecot versions < 1:2.3.21-19.el10_2.8. Fixed in 1:2.3.21-19.el10_2.8. How to fix ↓
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Background
Dovecot is a widely used IMAP server for Linux and UNIX-like systems, designed with a strong emphasis on security. It also includes a POP3 server and supports email storage in maildir or mbox formats. Dovecot's architecture allows for extensibility through SQL drivers and authentication plugins, making it a popular choice for email services. However, recent vulnerabilities have been identified that could compromise its security and functionality.
Vulnerability Detail
The vulnerabilities in Dovecot include a Denial of Service (DoS) via the IMAP ID command with excessive parameters, an authentication bypass due to incorrect OAuth2 token validation, and multiple DoS scenarios triggered by crafted email headers, truncated arguments in ManageSieve, and connection limit exhaustion. Additionally, there is a risk of arbitrary code execution through a use-after-free vulnerability in the Sieve editheader feature. These vulnerabilities can lead to service interruptions, unauthorized access, and potential data loss.
How To Fix
Minimum fixed version
1:2.3.21-19.el10_2.8
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 measure, you can limit the number of simultaneous connections to the Dovecot server to mitigate the risk of connection limit exhaustion. This can be done by adjusting the configuration file located at /etc/dovecot/dovecot.conf. Add or modify the following line: 'service imap-login { # Limit the number of connections client_limit = 100 }'. This will help reduce the impact of the vulnerabilities until a full update can be applied.
Conclusion
The recent security update for Dovecot addresses critical vulnerabilities that could lead to Denial of Service, authentication bypass, and arbitrary code execution. It is crucial for users to update their installations to the patched version to maintain the security and integrity of their email services.
See every vulnerability recorded for dovecot →
FAQ
Dovecot is an open-source IMAP and POP3 server for Unix-like operating systems, designed to provide secure and efficient email services.
The vulnerabilities include Denial of Service attacks, authentication bypass, and arbitrary code execution, which can compromise the server's security.
You can use Vulert's playground at Vulert Scanner to check if your application is impacted by these vulnerabilities without needing to sign up.
If an immediate update is not possible, consider implementing temporary workarounds such as limiting the number of connections to the server.
For detailed information about the vulnerabilities, including CVSS scores and acknowledgments, refer to the CVE pages linked in the advisory.
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