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Sun Solaris priocntl(2) does not adequately validate path to kernel modules that implement lightweight process (LWP) scheduling policy

Vulnerability Note VU#683673

Original Release Date: 2002-12-05 | Last Revised: 2002-12-06

Overview

The Sun Solaris priocntl(2) function does not adequately validate a memory structure that specifies the name of a kernel module. As a result, a local attacker could execute arbitrary code with superuser privileges on a vulnerable system.

Description

The Sun Solaris priocntl(2) function provides the ability to control the scheduling of lightweight processes (LWPs). LWPs are grouped into several classes, each class having a different scheduling policy. The priocntl(2) command PC_GETCID can be used to get the class ID and attributes for a class of LWPs. The PC_GETCID command can take as an argument a pointer to a structure of type pcinfo_t that contains information about the class. A pcinfo_t structure includes a member called pc_clname that specifies the name of the class, and in certain cases, the name of a kernel module that implements the process scheduling policy for the class. priocntl(2) searches for the kernel module specified by pc_clname in /kernel/sched and /usr/kernel/sched.

priocntl(2) does not adequately validate the data in pc_clname. As demonstrated by the exploit code posted to the BugTraq mailing list, an attacker with local user privileges can:

    1. create an arbitrary kernel module and place it in a writable location (/tmp/module for instance),
    2. create an arbitrary pcinfo_t structure with pc_clname set to the location of the kernel module relative to /usr/kernel/sched (../../../tmp/module), and
    3. issue a priocntl(2) call using the PC_GETCID command and a pointer to the pcinfo_t structure created by the attacker.
    Since priocntl(2) accepts the relative path operators (../) in pc_clname, the attacker-supplied module will be loaded by the kernel, and the attacker can act with superuser privileges.

    A different aspect of this vulnerability is that priocntl(2) does not validate or authenticate the kernel module that is being loaded. A message posted to BugTraq suggests checking the permissions ownership of the module and its parent directories. Another option could be to check a cryptographic hash or signature before loading a module.

    Impact

    A local attacker could execute code with superuser privileges.

    Solution


    Apply Patch or Upgrade

    Sun Alert ID 49131 states that "A final resolution is pending completion."


    Change Location of /sched Directories

    Sun Alert ID 49131 includes a workaround that involves nesting the /sched directories deeply enough that they cannot be traversed in the space available in pc_clname.

    Vendor Information

    683673
     
    Affected   Unknown   Unaffected

    Sun Microsystems Inc.

    Notified:  December 02, 2002 Updated:  December 05, 2002

    Status

      Vulnerable

    Vendor Statement

    Sun confirms that the priocntl(2) vulnerability does affect all currently supported versions of Solaris:

    Solaris 2.6, 7, 8, and 9

    Sun has released a Sun Alert which describes a workaround until patches are available at:

    http://sunsolve.Sun.COM/pub-cgi/retrieve.pl?doc=fsalert/49131

    The Sun Alert will be updated with the patch information once it becomes available. Sun patches are available from:

    http://sunsolve.sun.com/securitypatch

    Vendor Information

    The vendor has not provided us with any further information regarding this vulnerability.

    Addendum

    The CERT/CC has no additional comments at this time.

    If you have feedback, comments, or additional information about this vulnerability, please send us email.


    CVSS Metrics

    Group Score Vector
    Base N/A N/A
    Temporal N/A N/A
    Environmental N/A

    References

    Credit

    This vulnerability was publicly reported by CatDog.

    This document was written by Art Manion.

    Other Information

    CVE IDs: CVE-2002-1296
    Severity Metric: 20.48
    Date Public: 2002-11-27
    Date First Published: 2002-12-05
    Date Last Updated: 2002-12-06 17:12 UTC
    Document Revision: 42

    Sponsored by the Department of Homeland Security Office of Cybersecurity and Communications.