Ubuntu versions prior to 15.10 suffer from a PT chown arbitrary PTs access via user namespace privilege escalation vulnerability.
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Ubuntu Security Notice 2985-1 - Martin Carpenter discovered that pt_chown in the GNU C Library did not properly check permissions for tty files. A local attacker could use this to gain administrative privileges or expose sensitive information. Robin Hack discovered that the Name Service Switch (NSS) implementation in the GNU C Library did not properly manage its file descriptors. An attacker could use this to cause a denial of service (infinite loop). Various other issues were also addressed.
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