Multiple vulnerabilities has been identified and fixed in php:

Use-after-free vulnerability in the substr_replace function in PHP
5.3.6 and earlier allows context-dependent attackers to cause a
denial of service (memory corruption) or possibly have unspecified
other impact by using the same variable for multiple arguments
(CVE-2011-1148).

The (1) ZipArchive::addGlob and (2) ZipArchive::addPattern functions
in ext/zip/php_zip.c in PHP 5.3.6 allow context-dependent attackers
to cause a denial of service (application crash) via certain flags
arguments, as demonstrated by (a) GLOB_ALTDIRFUNC and (b) GLOB_APPEND
(CVE-2011-1657).

Stack-based buffer overflow in the socket_connect function in
ext/sockets/sockets.c in PHP 5.3.3 through 5.3.6 might allow
context-dependent attackers to execute arbitrary code via a long
pathname for a UNIX socket (CVE-2011-1938).

The rfc1867_post_handler function in main/rfc1867.c in PHP before
5.3.7 does not properly restrict filenames in multipart/form-data
POST requests, which allows remote attackers to conduct absolute
path traversal attacks, and possibly create or overwrite arbitrary
files, via a crafted upload request, related to a file path injection
vulnerability. (CVE-2011-2202).

crypt_blowfish before 1.1, as used in PHP before 5.3.7 on certain
platforms, does not properly handle 8-bit characters, which makes
it easier for context-dependent attackers to determine a cleartext
password by leveraging knowledge of a password hash (CVE-2011-2483).

PHP before 5.3.7 does not properly check the return values of
the malloc, calloc, and realloc library functions, which allows
context-dependent attackers to cause a denial of service (NULL
pointer dereference and application crash) or trigger a buffer
overflow by leveraging the ability to provide an arbitrary value
for a function argument, related to (1) ext/curl/interface.c, (2)
ext/date/lib/parse_date.c, (3) ext/date/lib/parse_iso_intervals.c,
(4) ext/date/lib/parse_tz.c, (5) ext/date/lib/timelib.c, (6)
ext/pdo_odbc/pdo_odbc.c, (7) ext/reflection/php_reflection.c,
(8) ext/soap/php_sdl.c, (9) ext/xmlrpc/libxmlrpc/base64.c, (10)
TSRM/tsrm_win32.c, and (11) the strtotime function (CVE-2011-3182).

PHP before 5.3.7 does not properly implement the error_log function,
which allows context-dependent attackers to cause a denial of service
(application crash) via unspecified vectors (CVE-2011-3267).

Buffer overflow in the crypt function in PHP before 5.3.7 allows
context-dependent attackers to have an unspecified impact via a
long salt argument, a different vulnerability than CVE-2011-2483
(CVE-2011-3268).

The updated php packages have been upgraded to 5.3.8 which is not
vulnerable to these issues.

Additionally some of the PECL extensions has been upgraded and/or
rebuilt for the new php version.