For full changes, please refer:
http://dev.mysql.com/doc/refman/5.1/en/news-5-1-51.html
Here is summary for security fixes:
* Security Fix: During evaluation of arguments to extreme-value
functions (such as LEAST() and GREATEST()), type errors did not
propagate properly, causing the server to crash. (Bug#55826)
* Security Fix: The server could crash after materializing a derived
table that required a temporary table for grouping. (Bug#55568)
* Security Fix: A user-variable assignment expression that is
evaluated in a logical expression context can be precalculated in a
temporary table for GROUP BY. However, when the expression value is
used after creation of the temporary table, it was re-evaluated, not
read from the table and a server crash resulted. (Bug#55564)
* Security Fix: Pre-evaluation of LIKE predicates during view
preparation could cause a server crash. (Bug#54568)
* Security Fix: GROUP_CONCAT() and WITH ROLLUP together could cause a
server crash. (Bug#54476)
* Security Fix: Queries could cause a server crash if the GREATEST()
or LEAST() function had a mixed list of numeric and LONGBLOB
arguments, and the result of such a function was processed using an
intermediate temporary table. (Bug#54461)
* Security Fix: Queries with nested joins could cause an infinite loop
in the server when used from stored procedures and prepared
statements. (Bug#53544)
* Security Fix: The PolyFromWKB() function could crash the server when
improper WKB data was passed to the function. (Bug#51875)
703045ddd2