Vulnerability Note VU#10277

When performing the "<<" redirection, /bin/sh creates a temporary file in /tmp with a name based on the process id, writes subsequent input out to that file, and then closes the file before re-opening it as the standard input of the command to be executed. At no stage are the results of the creat(), write(), or open() calls checked for an error status.

It is possible for another user to alter what is read from this file.

• If the sticky bit is not set on /tmp, the file can be simply removed, and a new file created in its place
• If the sticky bit is set, then it is possible to guess what the file will be called and create it before /bin/sh does (the creat() call performed by the shell does not result in an open() call with O_EXCL set) and hence it is possible to maintain a handle on the underlying file.
• If a fifo is created in place of the temporary file it is particularly easy to insert an extra command into the input transparently, and without having to worry about ensuring the bug is exploited during the narrow window of time in which it occurs.

Apply vendor patches; see the Systems Affected section below.

Avoid the use of << operator in cron jobs and similar administration scripts.