An Apache HTTP Server security update has been released for Ubuntu Linux 18.04 LTS, 20.04 LTS, 20.10, and 21.04.

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Ubuntu Security Notice USN-4994-1
June 21, 2021

apache2 vulnerabilities
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A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 21.04
- Ubuntu 20.10
- Ubuntu 20.04 LTS
- Ubuntu 18.04 LTS

Summary:

Several security issues were fixed in Apache HTTP Server.

Software Description:
- apache2: Apache HTTP server

Details:

Marc Stern discovered that the Apache mod_proxy_http module incorrectly
handled certain requests. A remote attacker could possibly use this issue
to cause Apache to crash, resulting in a denial of service. This issue only
affected Ubuntu 20.04 LTS, Ubuntu 20.10, and Ubuntu 21.04. (CVE-2020-13950)

Antonio Morales discovered that the Apache mod_auth_digest module
incorrectly handled certain Digest nonces. A remote attacker could possibly
use this issue to cause Apache to crash, resulting in a denial of service.
(CVE-2020-35452)

Antonio Morales discovered that the Apache mod_session module incorrectly
handled certain Cookie headers. A remote attacker could possibly use this
issue to cause Apache to crash, resulting in a denial of service.
(CVE-2021-26690)

Christophe Jaillet discovered that the Apache mod_session module
incorrectly handled certain SessionHeader values. A remote attacker could
use this issue to cause Apache to crash, resulting in a denial of service,
or possibly execute arbitrary code. (CVE-2021-26691)

Christoph Anton Mitterer discovered that the new MergeSlashes configuration
option resulted in unexpected behaviour in certain situations.
(CVE-2021-30641)

Update instructions:

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

Ubuntu 21.04:
apache2 2.4.46-4ubuntu1.1
apache2-bin 2.4.46-4ubuntu1.1

Ubuntu 20.10:
apache2 2.4.46-1ubuntu1.2
apache2-bin 2.4.46-1ubuntu1.2

Ubuntu 20.04 LTS:
apache2 2.4.41-4ubuntu3.3
apache2-bin 2.4.41-4ubuntu3.3

Ubuntu 18.04 LTS:
apache2 2.4.29-1ubuntu4.16
apache2-bin 2.4.29-1ubuntu4.16

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

References:
  https://ubuntu.com/security/notices/USN-4994-1
CVE-2020-13950, CVE-2020-35452, CVE-2021-26690, CVE-2021-26691,
CVE-2021-30641

Package Information:
  https://launchpad.net/ubuntu/+source/apache2/2.4.46-4ubuntu1.1
  https://launchpad.net/ubuntu/+source/apache2/2.4.46-1ubuntu1.2
  https://launchpad.net/ubuntu/+source/apache2/2.4.41-4ubuntu3.3
  https://launchpad.net/ubuntu/+source/apache2/2.4.29-1ubuntu4.16