Based on MySQL 5.5.28, including all the bug fixes in it, Percona Server 5.5.28-29.3 is now the current stable release in the 5.5 series. All of Percona‘s software is open-source and free, all the details of the release can be found in the 5.5.28-29.3 milestone at Launchpad.
Fixed the upstream bug #66550 and the security vulnerability CVE-2012-4414. This was caused because user-supplied identifiers (table names, field names, etc.) are not always properly quoted, so authorized users that have privileges to modify a table (any non-temporary table) can inject arbitrary SQL into the binary log and that could cause multiple SQL injection like vulnerabilities. This bug fix comes originally from MariaDB (see MDEV-382). Bug fixed #1049871 (Vlad Lesin).
Fixed the upstream bug #67685 and the security vulnerability CVE-2012-5611. This vulnerability allowed remote authenticated users to execute arbitrary code via a long argument to the GRANT FILE command. This bug fix comes originally from MariaDB (see MDEV-3884). Bug fixed #1083377 (Vlad Lesin).
Rows_read was calculated in a way which lead to a negative value being printed in the slow query log. Fixed by making Rows_read to be a synonym for Rows_examined in the slow query log. Bug fixed #830286 (Alexey Kopytov).
Fixed the upstream bug #66237. Temporary files created by binary log cache were not purged after transaction commit. Fixed by truncating the temporary file, if used for a binary log transaction cache, when committing or rolling back a statement or a transaction. Bug fixed #1070856 (Alexey Kopytov).
Values for Rows_sent and Rows_read would be identical in the Slow Query Log. This bug was introduced when slow_extended.patch was ported to Percona Server 5.5. Fixed by making Rows_read identical to Rows_examined instead. Bug fixed #721176 (Alexey Kopytov).
Fixed unsigned math error in fsp_reserve_free_extents that in some specific cases would cause the function to believe that billions more extents have been reserved than have actually been reserved. Bug fixed #1083700 (George Ormond Lorch III).
When mysqldump was used with --innodb-optimize-keys, it did not handle composite indexes correctly when verifying if the optimization is applicable with respect to AUTO_INCREMENT columns. Bug fixed #1039536 (Alexey Kopytov).
In cases where indexes with AUTO_INCREMENT columns where correctly detected, mysqldump prevented all such keys from optimization, even though it is sufficient to skip just one (e.g. the first one). Bug fixed #1081003 (Alexey Kopytov).
Other bug fixes: bug fixed #1071986 (Alexey Kopytov), bug fixed #901060 (Laurynas Biveinis), bug fixed #1090596 (Stewart Smith), bug fixed #1087202 (Vladislav Vaintroub, Laurynas Biveinis) and bug fixed #1087218 (Vladislav Vaintroub, Laurynas Biveinis).