Published: 28 February 2011
The proc filesystem implementation in the Linux kernel 2.6.37 and earlier does not restrict access to the /proc directory tree of a process after this process performs an exec of a setuid program, which allows local users to obtain sensitive information or cause a denial of service via open, lseek, read, and write system calls.
From the Ubuntu security team
It was discovered that the /proc filesystem did not correctly handle permission changes when programs executed. A local attacker could hold open files to examine details about programs running with higher privileges, potentially increasing the chances of exploiting additional vulnerabilities.