Source:
http://int21.de/cve/CVE-2008-0124-s9y.html

References

http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2008-0124
http://blog.s9y.org/archives/191-Serendipity-1.3-beta1-released.html
http://hboeck.de/archives/591-Cross-Site-Scripting-XSS-in-the-backend-and-in-the-installer.html
Description

Serendipity (S9Y) is a popular blogging system.
If used in a multiuser environment, one user can inject javascript code into 
certain fields in the backend to steal the cookies and hijack the accounts of 
other users.

Serendipity has the trustxss plugin to prevent XSS between users on multiuser 
setups, but that doesn't catch these issues.

In the »Personal Settings«-Dialogue, the »Real name« field can be filled with 
javascript, which appears on newly written articles. The »Username« field can 
also contain javascript, but there's no attack vector, as this field is only 
shown to the user itself.

Beside, the media library accepts uploads from any file format, including htm, 
html and js, which obviously also leads to xss.
Workaround/Fix

If you have a multiuser-blog and don't trust all users, you need to install 
the trustxss plugin and should immediately upgrade to 1.3-beta1.
If you're using a single-user blog, you are not affected.
Disclosure Timeline

2008-02-01 Vendor contacted
2008-02-01 Vendor fixed svn
2007-02-25 Vendor released 1.3-beta1
CVE Information

The Common Vulnerabilities and Exposures (CVE) project has assigned the name 
CVE-2008-0124 to this issue. This is a candidate for inclusion in the CVE 
list (http://cve.mitre.org/), which standardizes names for security problems.
Credits and copyright

This vulnerability was discovered by Hanno Boeck of schokokeks.org webhosting. 
It's licensed under the creative commons attribution license.

Hanno Boeck, 2008-02-26, http://www.hboeck.de

-- 
Hanno Böck    Blog:    http://www.hboeck.de/
GPG: 3DBD3B20    Jabber/Mail:  hanno@hboeck.de