A dovecot security update has been released for Debian GNU/Linux 9 LTS to address several vulnerabilities.

DLA 2328-1: dovecot security update

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Debian LTS Advisory DLA-2328-1 debian-lts@lists.debian.org
  https://www.debian.org/lts/security/
August 15, 2020   https://wiki.debian.org/LTS
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Package : dovecot
Version : 1:2.2.27-3+deb9u6
CVE ID : CVE-2020-12100 CVE-2020-12673 CVE-2020-12674
Debian Bug : 968302

Several vulnerabilities have been discovered in the Dovecot email
server.

CVE-2020-12100

Receiving mail with deeply nested MIME parts leads to resource
exhaustion as Dovecot attempts to parse it.

CVE-2020-12673

Dovecot's NTLM implementation does not correctly check message
buffer size, which leads to a crash when reading past allocation.

CVE-2020-12674

Dovecot's RPA mechanism implementation accepts zero-length message,
which leads to assert-crash later on.

For Debian 9 stretch, these problems have been fixed in version
1:2.2.27-3+deb9u6.

We recommend that you upgrade your dovecot packages.

For the detailed security status of dovecot please refer to
its security tracker page at:
  https://security-tracker.debian.org/tracker/dovecot

Further information about Debian LTS security advisories, how to apply
these updates to your system and frequently asked questions can be
found at:   https://wiki.debian.org/LTS