apache2 vulnerabilities

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)