Software Engineering Institute

Gzip is a utility used for compressing and decompressing files. The "-f" (-force) flag is used to force compression or decompression even if the file has multiple hard links. When gzip is used with the "-f" flag on a Sun Solaris 8 machine, it may change the permissions of a hard linked file to 0777, causing a hard link to become readable and able to be modified by unprivileged users, regardless of its previous permission settings.

Note that Solaris 7 and Solaris 9 are not affected by this issue. This vulnerability is only present in versions of gzip prior to 1.3.

The following describes the symptoms of the vulnerability (example provided by the SunSolve Alert) :

    $ ln original-file hardlink
   $ ls -l original-file hardlink
   -rw-r--r--   2 user  staff        293 Jun 24 18:33 hardlink
   -rw-r--r--   2 user  staff        293 Jun 24 18:33 original-file
   $ gzip -f original-file
   $ ls -l original-file* hardlink
   -rwxrwxrwx   1 user  staff        293 Jun 24 18:33 hardlink
   -rw-r--r--   1 user  staff        195 Jun 24 18:33 original-file.gz

Local unprivileged users may be able to read or modify files owned by the user who has invoked gzip as described. Access to system files may inadvertently be granted if the gzip command is issued by a local privileged user.

Apply a patch

SPARC platform: Install Solaris 8 patch 112668-02 or later.
x86 platform: Install Solaris 8 patch 112669-02 or later.

Do not use the force option for gzip

Per Sun Alert ID 57600, avoid using the "-f" or "-force" option with the vulnerable gzip command to work around the problem.