安全性

With this update, the default Fedora policy regarding cryptographic components has been updated to disallow the use of algorithms that are no longer considered secure. Specifically, the changes involve:

With this update, the libcurl library switches from using libssh2 to implement the SSH layer of SCP and SFTP protocols to libssh. The reason for the change is that the libssh2 library uses outdated cryptographic algorithms and lacks important features, such as GSS-API authentication. The newly used libssh library is more secure, feature-complete, and with more active upstream community.

In Fedora 28, the default file format used by the NSS library is changed to SQL.

The Network Security Services (NSS) library, which is used by Mozilla Firefox, Gnome Evolution, Mozilla Thunderbird, and other applications, changed its default database format for storing keys, certificates, and trust information. The new database format is based on SQlite and uses the filenames cert9.db, key4.db, and pkcs11.txt. The previous database format used Berkeyley DB (DBM) and filenames cert8.db, key3.db, and secmod.db.

The primary benefit of the SQlite storage is support for concurrent access by multiple applications. When using the previous default file format based on DBM, accidental concurrent access could result in corrupted storage.

Unless an application explicitly requests either the DBM or SQL format, the NSS library will automatically migrate the application’s NSS database from the old to the new format. The old database files will not be updated further. Most users should not experience differences in operation. Applications that perform many NSS read/write operations may experience a minor performance decrease. Use the following command to trigger an explicit migration:

Users who store their system home or application data directory on a network filesystem are advised to set the NSS_SDB_USE_CACHE=yes environment variable prior to starting applications that use NSS. Without setting this environment variable, users of network filesystems may experience a major slowdown with some applications, such as Firefox. The environment variable enables the use of a caching strategy in NSS that works around the slowness of network filesystems. Because this caching strategy causes a performance decrease on fast filesystems.

Additional technical details can be found in the Fedora Wiki: https://fedoraproject.org/wiki/Changes/NSSDefaultFileFormatSql.

Fedora 28 removes support for tcp_wrappers (aka /etc/hosts.deny access files) by default from all the network daemons and tools. The preferred replacements are software firewalld, nftables rules or software specific access rules for more complex filtering. If your system security depends on tcp_wrappers rules, convert them to firewall rules, or set up tcpd to do the same job for you.

With this update, the OpenLDAP distribution in Fedora changed from using the NSS (or MozNSS) library to the OpenSSL library for providing cryptographic functions. The switch promises better support from OpenLDAP upstream, which had ceased maintaining the NSS support layer.

OpenLDAP clients and server now use the system-wide certificate store by default, instead of /etc/openldap/certs.

Fedora has deprecated the use of TCP wrappers. The OpenLDAP project also discourages their use and recommends that an IP firewall is used instead. With this update, OpenLDAP will not be configured with --enable-wrappers and so any TCP wrappers configuration will have no effect on OpenLDAP. Other means should be used to protect the OpenLDAP server.

Fedora 28 replaces authconfig with authselect as the default tool for generating PAM configuration files and nsswitch.conf. On new installations, authselect, together with an authconfig compatibility tool, will be installed by default instead of authconfig. On upgraded installations, authconfig will be replaced with authselect and the compatibility tool but the configuration generated by authconfig will be left intact. The authconfig compatibility tool will be removed from Fedora in a future release. The authselect-migration(7) man page explains how to migrate from authconfig to authselect.