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CVE 2009-2672

The proxy mechanism implementation in Sun Java Runtime Environment (JRE) in JDK and JRE 6 before Update 15, and JDK and JRE 5.0 before Update 20, does not prevent access to browser cookies by untrusted (1) applets and (2) Java Web Start applications, which allows remote attackers to hijack web sessions via unspecified vectors.

See the CVE page on Mitre.org for more details.