Paul Starzetz discovered a flaw in bounds checking in mremap() in the Linux kernel (present in version 2.4.x and 2.6.x) which may allow a local attacker to gain root privileges. Version 2.2 is not affected by this bug, since it doesn't support the MREMAP_FIXED flag (as clarified later).
For the stable distribution (woody) this problem has been fixed in kernel-source version 2.4.18-14.1 and kernel-images versions 2.4.18-12.1 and 2.4.18-5woody6 (bf) for the i386 architecture.
For the unstable distribution (sid) this problem will be fixed soon with newly uploaded packages.
We recommend that you upgrade your kernel packages. This problem has been fixed in the upstream version 2.4.24 as well.