Apache Hadoop before 0.23.4, 1.x before 1.0.4, and 2.x before 2.0.2 generate token passwords using a 20-bit secret when Kerberos security features are enabled, which makes it easier for context-dependent attackers to crack secret keys via a brute-force attack.

The Kerberos/MapReduce security functionality in Apache Hadoop 0.20.203.0 through 0.20.205.0, 0.23.x before 0.23.2, and 1.0.x before 1.0.2, as used in Cloudera CDH CDH3u0 through CDH3u2, Cloudera hadoop-0.20-sbin before 0.20.2+923.197, and other products, allows remote authenticated users to impersonate arbitrary cluster user accounts via unspecified vectors.

It was reported [1] that:

"The Apache Hadoop RPC protocol is intended to provide bidirectional authentication between clients and servers. However, a malicious server or network attacker can unilaterally disable these authentication checks. This allows for potential reduction in the configured quality of protection of the RPC traffic, and privilege escalation if authentication credentials are passed over RPC."

This flaw only affects users who have enabled Hadoop's kerberos security features. This is corrected in upstream versions 0.23.9, 1.2.1, and 2.0.6-alpha.

[1] http://seclists.org/fulldisclosure/2013/Aug/251