Will Drewry discovered that Horde allows remote attackers to send an email with a crafted MIME attachment filename attribute to perform cross site scripting.
For the stable distribution (etch), this problem has been fixed in version 3.1.3-4etch4.
For the testing distribution (lenny), this problem has been fixed in version 3.2.1+debian0-2+lenny1.
For the unstable distribution (sid), this problem will be fixed soon.
We recommend that you upgrade your horde3 package.
MD5 checksums of the listed files are available in the original advisory.