As reported here last week, three security flaws had been discovered that impacted upon the 2.6.x Kernel. A NULL-pointer dereference within netfilter when handling SCTP connections with unknown chunk types that could be exploited to crash the kernel; a cpuset_task_read() function in /kernel/cpuset.c which had an underflow error that could potentially be exploited in order to read the kernel memory; and a problem whereby the kernel itself mishandled seeds for random number generation, potentially weakening application security for those programs relying upon secure random number generation.
The latest update also fixes a number of other problems, such as the regression in the smbfs subsystem introduced in DSA-1233 causing symlinks to be interpreted as regular files.
Debian recommend that you upgrade your kernel package immediately and reboot the machine, and if you have built a custom kernel from the kernel source package that you rebuild to take advantage of the new fixes.
Just to help, the upgrade instructions are:
wget url (to fetch the file for you)
dpkg -i file.deb (to install the referenced file)
And for those of you using the apt-get package manager:
apt-get update (to update the internal database)
apt-get upgrade (to install corrected packages)