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Ubuntu Security Notice USN-4994-2
June 21, 2021

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

- Ubuntu 16.04 ESM
- Ubuntu 14.04 ESM

Summary:

Several security issues were fixed in Apache HTTP Server.

Software Description:
- apache2: Apache HTTP server

Details:

USN-4994-1 fixed several vulnerabilities in Apache. This update provides
the corresponding update for Ubuntu 14.04 ESM and Ubuntu 16.04 ESM.

Original advisory details:

 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 16.04 ESM:
  apache2                         2.4.18-2ubuntu3.17+esm1
  apache2-bin                     2.4.18-2ubuntu3.17+esm1

Ubuntu 14.04 ESM:
  apache2                         2.4.7-1ubuntu4.22+esm1
  apache2-bin                     2.4.7-1ubuntu4.22+esm1

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

References:
  https://ubuntu.com/security/notices/USN-4994-2
  https://ubuntu.com/security/notices/USN-4994-1
  CVE-2020-35452, CVE-2021-26690, CVE-2021-26691, CVE-2021-30641