# 12 Upgrade notes for 3.4.2

#### URI validation

A new ZBX\_URI\_VALID\_SCHEMES
[constant](/manual/web_interface/definitions) has been added which
defines the URI schemes that are allowed by default (*http*, *https*,
*ftp*, *file*, *mailto*, *tel*, *ssh*).

All URLs in the frontend should be checked if they contain an allowed
scheme.

Note that starting with [Zabbix
3.4.5](/manual/introduction/whatsnew345#configurable_uri_validation),
URI scheme validation can be turned off/on.

#### Acknowledgement message recipient options

The option list for acknowledgement message recipients has been
reworked. See [What's
new](/manual/introduction/whatsnew342#acknowledgement_message_recipient_option)
for more details.

#### Permission changes to dashboards

Permissions to dashboards have been changed for the Zabbix Admin type of
users. See [What's
new](/manual/introduction/whatsnew342#permission_changes_to_dashboards)
for more details.

#### Processing low-level discovery (LLD)

LLD rule processing has been modified so multiple values for the same
LLD rule are not processed simultaneously.

Previously all values for LLD rules were processed in a context of data
gathering process (for example, a trapper). This could cause deadlocks
when separate values of a single low-level discovery rule were being
processed in more than one data gathering process.

LLD rule locking is implemented in the configuration cache. A new piece
of LLD data will be discarded if the previous one hasn't been fully
processed yet. To avoid such possible delays with LLD value processing
it is recommended, for example, to increase the polling interval for LLD
rules or not send LLD JSONs with zabbix\_sender too frequently.
Discarded LLD data is not considered an error. zabbix\_sender can report
a value as "processed" even if the value was discarded. All cases of
discarded LLD data are listed in the Zabbix server log file in the
following format:

    <TIMESTAMP> cannot process discovery rule "host:key": another value is being processed

#### SMTP authentication for e-mail

Previously Zabbix would enforce PLAIN as the
[authentication](/manual/config/notifications/media/email) mechanism
when using username/password. Now libcurl may decide on its own which
mechanism among those supported by the SMTP server to choose. With the
parameters Zabbix passes to libcurl it effectively means choosing
between PLAIN and LOGIN on most occasions. This is enough to enable
Zabbix operation with Office 365 and should be enough for Gmail provided
that "less secure apps" are
[allowed](https://support.google.com/accounts/answer/6010255).

#### Housekeeper changes

In previous 3.4.x versions, problems for a deleted item/trigger could
not get deleted by housekeeper if they were not in a resolved status.
From now on, if housekeeping of events is enabled then deleting an
item/trigger will also delete events and problems generated by that
item/trigger. If housekeeping of events is disabled then only problems
of a deleted item/trigger will get deleted.

An optional database patch to clean up problems for deleted items and
triggers has also been added.