A Dovecot security update has been released for Ubuntu 16.04 LTS, 18.04 LTS, 20.04 LTS, and 20.10.

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Ubuntu Security Notice USN-4674-1
January 04, 2021

dovecot vulnerabilities
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A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 20.10
- Ubuntu 20.04 LTS
- Ubuntu 18.04 LTS
- Ubuntu 16.04 LTS

Summary:

Several security issues were fixed in Dovecot.

Software Description:
- dovecot: IMAP and POP3 email server

Details:

It was discovered that Dovecot incorrectly handled certain imap hibernation
commands. A remote authenticated attacker could possibly use this issue to
access other users' email. This issue only affected Ubuntu 18.04 LTS,
Ubuntu 20.04 LTS, and Ubuntu 20.10. (CVE-2020-24386)

Innokentii Sennovskiy discovered that Dovecot incorrectly handled MIME
parsing. A remote attacker could possibly use this issue to cause Dovecot
to crash, resulting in a denial of service. (CVE-2020-25275)

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 20.10:
dovecot-core 1:2.3.11.3+dfsg1-2ubuntu0.1

Ubuntu 20.04 LTS:
dovecot-core 1:2.3.7.2-1ubuntu3.3

Ubuntu 18.04 LTS:
dovecot-core 1:2.2.33.2-1ubuntu4.7

Ubuntu 16.04 LTS:
dovecot-core 1:2.2.22-1ubuntu2.14

In general, a standard system update will make all the necessary changes.

References:
  https://usn.ubuntu.com/4674-1
CVE-2020-24386, CVE-2020-25275

Package Information:
  https://launchpad.net/ubuntu/+source/dovecot/1:2.3.11.3+dfsg1-2ubuntu0.1
  https://launchpad.net/ubuntu/+source/dovecot/1:2.3.7.2-1ubuntu3.3
  https://launchpad.net/ubuntu/+source/dovecot/1:2.2.33.2-1ubuntu4.7
  https://launchpad.net/ubuntu/+source/dovecot/1:2.2.22-1ubuntu2.14