A Security Vulnerability in the ZFS Filesystem May Allow An Unprivileged User to Take Ownership of Files Belonging to Another User

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A Security Vulnerability in the ZFS Filesystem May Allow An Unprivileged User to Take Ownership of Files Belonging to Another User

1. Impact

A security vulnerability in the ZFS file system in OpenSolaris and Solaris 10 systems with patches 137137-09 (SPARC) or 137138-09 (x86) installed may allow a local unprivileged user with the 'file_chown_self' privilege to take ownership of files belonging to another user.

2. Contributing Factors

This issue can occur in the following releases:

SPARC Platform

• Solaris 10 with patch 137137-09 and without patch 141444-09
• OpenSolaris based upon builds snv_100 through snv_117

x86 Platform

• Solaris 10 with patch 137138-09 and without patch 141445-09
• OpenSolaris based upon builds snv_100 through snv_117

Notes:

1. Solaris 8 and 9 are not impacted by this issue.

2. OpenSolaris distributions may include additional bug fixes above and beyond the build from which it was derived. The base build can be derived as follows:

$ uname -v
snv_86

3. This issue only affects systems with ZFS file systems where local users have been granted the {PRIV_FILE_CHOWN_SELF} (see chown(2)) privilege which allows them to modify ownership of files where the ownership matches the user's current effective user ID. If the default operating system configuration option '{_POSIX_CHOWN_RESTRICTED}' has been disabled then the 'file_chown_self' privilege is asserted in the inheritable set of all processes unless overridden by policy.conf(4) or user_attr(4).

To determine if a system is using ZFS, the following command can be run:

$ zfs list

If there are any pools listed, then ZFS is being used.

To determine if a user has been given the privilege to give away ownership of a file, the following command can be run:

$ ppriv <pid> | grep "file_chown_self" || echo "User not authorized give away ownership of files"
E: basic,dtrace_kernel,dtrace_proc,dtrace_user,file_chown_self,proc_owner
I: basic,dtrace_kernel,dtrace_proc,dtrace_user,file_chown_self,proc_owner
P: basic,dtrace_kernel,dtrace_proc,dtrace_user,file_chown_self,proc_owner

and then check if the output lists 'file_chown_self'.

To determine if all users system wide have been given the privilege to give away ownership of a file, the following command can be run:

$ grep "set rstchown=0" /etc/system && echo "All users have privilege to give away ownership of a file"
All users have privilege to give away ownership of a file

3. Symptoms

There are no predictable symptoms that would indicate the described vulnerability has been exploited.

4. Workaround

There is no workaround for this issue. Please see the Resolution section below.

5. Resolution

This issue is addressed in the following releases:

SPARC Platform

• Solaris 10 with patch 141444-09 or later
• OpenSolaris based upon builds snv_118 or later

x86 Platform

• Solaris 10 with patch 141445-09 or later
• OpenSolaris based upon builds snv_118 or later

For more information on Security Sun Alerts, see Technical Instruction ID 213557.

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