Changeset 5052 a589a8dbde79 question (original) (raw)

Christopher Meyer christopher.meyer at rub.de
Fri Feb 24 13:31:56 UTC 2012

Hi, please correct me if I'm wrong, but the Changeset 5052 in ZoneInfoFile could maybe draw an unexpected SideChannel at System.err.

Please have a look at the following: TimeZone tzExistent = TimeZone.getTimeZone("/.\56/.\56/.\56/etc/passwd"); will walk the following path:

java.util.TimeZone: public static synchronized TimeZone getTimeZone(String ID) private static TimeZone getTimeZone(String ID, boolean fallback) private static final TimeZone parseCustomTimeZone(String id) sun.util.calendar.ZoneInfo public static ZoneInfo getZoneInfo(String id) private static ZoneInfo createZoneInfo(String id) private static byte[] readZoneInfoFile(final String fileName)

where it is checked if it contains ".."

ileName.indexOf("..") >= 0 (which indeed it doesn't) - no more checking at this point, necessary path checks are dropped for the sake of performance. When passed to

File file = new File(ziDir, fileName);

it will evalute fine to /../../../etc/passwd. Since the operation takes place inside a doPrivileged block the file could be read (if present) without SecurityException, even in an Applet. The attacker would succeed with a directory traversal. No big deal due to this point, since no information is handled to a potential attacker.

But when looking at the return path we find the following in private static ZoneInfo createZoneInfo(String id):

System.err.println("ZoneInfo: wrong magic number: " + id); or System.err.println("ZoneInfo: incompatible version (" + buf[index - 1] + "): " + id);

So if an attacker manages to access System.err (one could think about capabilities of LiveConnect or some related technologies...) he would be able to detect the presence of files on the victims system. This would be clearly a violation of the applet sandbox.

In my opinion the impact is not that big, but it increases an attackers surface.

Do I miss something or got something wrong or this this an issue that should be fixed?

Regards from Germany, Chris

Blog on Java security and related topics: armoredbarista.blogspot.com

Dipl.-Ing. Christopher Meyer

Horst Görtz Institute for IT-Security Chair for Network and Data Security Ruhr-University Bochum, Germany

Universitätsstr. 150, ID 2/415 D-44801 Bochum, Germany http:// www.nds.rub.de

Phone: (+49) (0)234 / 32 - 29815 Fax: (+49) (0)234 / 32 - 14347

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