This evening we were notified by fellow co-developer Sebastian Nohn about a full-disclosure posting about a Serendipity SQL injection matter. We have investigated this reported 0day issue, and can tell you that it is not a SQL injection,but instead "only"an SQL error display.
No SQL can be injected using the described method. Because of an invalid category ID, serendipity tries to show entries for that category, but the resulting SQL string contains an emtpy "(())" statement which makes the MySQL parser fail, and report the error on-screen. The SQL queries that Serendipity uses are not secret, and could be looked up in the sourcecode as well.
Even though we consider this issue to be fairly low-impact, Serendipity 1.1.2 has been released because of this, mainly to assure the public that we have addressed the issue. It is not critical that you upgrade to that release. If you do, it is sufficient to update the include/functions_entries.inc.php file. The only change made to that function is documented here
We would also like to express, that we kindly appreciate all bug and security reports about Serendipity, and take them and our responsibility very seriously. Also rest assured that if you contact us developer first before publishing security advisories, we always cooperate, pay credit and fix issues immediately, as we have done in the past. So we look forward to working together with SaMuschie in the future, who seems to taking some serious work in checking security issues - good work on that! :-)
The latest release can be downloaded here. This fix has also been committed to the daily snapshots.