The remote Debian host is missing a security-related update.
A flaw was discovered in mediawiki, a wiki engine: thumb.php outputs wikitext messages as raw HTML, potentially leading to cross-site scripting (XSS).
Upgrade the mediawiki packages. For the stable distribution (wheezy), this problem has been fixed in version 1.19.20+dfsg-0+deb7u3; this version additionally fixes a regression introduced in the previous release, DSA-3100-1. For the upcoming stable distribution (jessie) and unstable distribution (sid), this problem has been fixed in version 1:1.19.20+dfsg-2.2.