An OpenSMTPD security update has been released for Ubuntu Linux 19.10 and 18.04 LTS to address several security issues.

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Ubuntu Security Notice USN-4294-1
March 02, 2020

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

- Ubuntu 19.10
- Ubuntu 18.04 LTS

Summary:

Several security issues were fixed in opensmtpd.

Software Description:
- opensmtpd: secure, reliable, lean, and easy-to configure SMTP server

Details:

It was discovered that OpenSMTPD mishandled certain input. A remote,
unauthenticated attacker could use this vulnerability to execute arbitrary
shell commands as any non-root user. (CVE-2020-8794)

It was discovered that OpenSMTPD did not properly handle hardlinks under
certain conditions. An unprivileged local attacker could read the first
line of any file on the filesystem. (CVE-2020-8793)

Update instructions:

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

Ubuntu 19.10:
opensmtpd 6.0.3p1-6ubuntu0.2

Ubuntu 18.04 LTS:
opensmtpd 6.0.3p1-1ubuntu0.2

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

References:
  https://usn.ubuntu.com/4294-1
CVE-2020-8793, CVE-2020-8794

Package Information:
  https://launchpad.net/ubuntu/+source/opensmtpd/6.0.3p1-6ubuntu0.2
  https://launchpad.net/ubuntu/+source/opensmtpd/6.0.3p1-1ubuntu0.2