A trivially-exploitable bug was discovered in webcalendar that allows an attacker to execute arbitrary code with the privileges of the HTTP daemon on a system running a vulnerable version.
The old stable distribution (woody) does not contain the webcalendar package.
For the stable distribution (sarge) this problem has been fixed in version 0.9.45-4sarge2.
For the unstable distribution (sid) this problem will be fixed shortly.
We recommend that you upgrade your webcalendar package immediately.