[VulnWatch] High Risk Flaw in Sun's Java Web Start

John Heasman of NGSSoftware has discovered a high risk vulnerability in Sun Microsystem's Java Web Start that ships with the JRE and JDK on Windows platforms.

The vulnerability affects the following version of Java Web Start:

Java Web Start in JDK and JRE 5.0 Update 11 and earlier
Java Web Start in SDK and JRE 1.4.2_13 and earlier

This vulnerability permits an untrusted Java Web Start application to overwrite any file that can be accessed under the application user context. This ultimately enables an untrusted application to break out of the sandbox by modifying the user's Java security policy. An untrusted application could be launched via a malicious web page.

The JNLP API defines a set of services that bypass the security sandbox to enable some common client operations. The BasicService is used to discover the application's codebase. Then, the PersistenceService caches content on the local hard drive, keyed to a URL that is relative to the application's base. The name/value pairs provided by the PersistenceService are similar to browser cookies. The Java Web Start implementation honours this legacy by naming the pairs "muffins".

Arbitrary files can be written to due to a directory traversal flaw in the PersistenceService.

This issue has now been resolved; further details are available at: http://sunsolve.sun.com/search/document.do?assetkey=1-26-102957-1

NGSSoftware Insight Security Research
+44(0)208 401 0070


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