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            Caldera International, Inc. Security Advisory

Subject: OpenServer: setcontext and sysi86 vulnerabilities
Advisory number: CSSA-2001-SCO.35
Issue date: 2001 November 29
Cross reference:
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1. Problem Description
        
        This patch closes a family of security holes present in SCO
        OpenServer 5.0.6 and previous releases, which stem from the
        ability of regular user processes to reprogram segment
        descriptors and certain other CPU registers.

        Closing this family of security holes does, however, result in
        a functionality change which may prevent certain applications
        from running -- they will exit with an error, or dump core,
        instead of running properly. For example, the i286emul and
        x286emul emulators will not work, so any '286 executables
        which require those emulators will not work. It is our
        intention to enhance this patch in the future, such that it
        enables full functionality of such applications while still
        closing the security holes.

        If this patch breaks any crucial applications, the system
        administrator may choose to disable the patch, by editing the
        file /etc/conf/pack.d/kernel/space.c and setting the value of
        the allow_dscr_remap parameter to 1. This will return the
        kernel to the old (not-secure) behavior.

2. Vulnerable Versions

        Operating System Version Affected Files
        ------------------------------------------------------------------
        OpenServer All /etc/conf/pack.d/kernel/os.a(machdep.o)
                                        /etc/conf/pack.d/kernel/os.a(sysi86.o)

3. Workaround

        None.

4. OpenServer

  4.1 Location of Fixed Binaries

        ftp://stage.caldera.com/pub/security/openserver/CSSA-2001-SCO.35/

  4.2 Verification

        md5 checksums:
        
        89a6894b514d0175676d12745158aaea VOL.000.000

        md5 is available for download from

                ftp://stage.caldera.com/pub/security/tools/

  4.3 Installing Fixed Binaries

        Upgrade the affected binaries with the following commands:

        Download the VOL.000.000 file to /tmp
        
        # custom

        Instruct custom to install from images, and supply /tmp as the
        directory of the VOL image.

5. References

        ftp.netbsd.org/pub/NetBSD/security/advisories/NetBSD-SA2001-002.txt.asc

        This and other advisories are located at
                http://stage.caldera.com/support/security

        This advisory addresses Caldera Security internal incidents
        sr855993, sr855994, SCO-559-1328, SCO-559-1329, erg711906 and
        erg711905.

6. Disclaimer

        Caldera International, Inc. is not responsible for the misuse
        of any of the information we provide on our website and/or
        through our security advisories. Our advisories are a service
        to our customers intended to promote secure installation and
        use of Caldera International products.

7. Acknowledgements

        Caldera wishes to thank the Last Stage of Delirium Research
        Group (contactlsd-pl.net) for their discovering of, and
        research into, these issues.

         
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