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                   Red Hat, Inc. Security Advisory



Synopsis:          tmpwatch has a local denial of service and root exploit

Advisory ID:       RHSA-2000:080-01

Issue date:        2000-10-06

Updated on:        2000-10-06

Product:           Red Hat Linux

Keywords:          tmpwatch, fuser, DoS, fork

Cross references:  N/A

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1. Topic:



tmpwatch as shipped in Red Hat Linux 6.1, 6.2, and 7.0 uses fork() to

recursively process subdirectories, enabling a local user to perform a

denial of service attack.  Tmpwatch from Red Hat Linux 6.2 and 7.0 also

contains an option to allow it to use the fuser command to check for open

files before removal. It executed fuser in an insecure fashion, allowing a

local root exploit.



2. Relevant releases/architectures:



Red Hat Linux 6.1 - i386, alpha, sparc

Red Hat Linux 6.2 - i386, alpha, sparc

Red Hat Linux 7.0 - i386



3. Problem description:



The tmpwatch program periodically cleans up files in temporary directories

by removing all files older than a certain age.  In Red Hat Linux 6.1, 6.2,

and 7.0, it used fork() to recursively process subdirectories.  If a

malicious user created many layers of subdirectories (thousands) in a

temporary directory monitored by tmpwatch, the system process table would

fill up, requiring a reboot.



Additionally, tmpwatch in 6.2 and 7.0 contains an option, "--fuser", that

attempts to user the fuser command to check if a file is in use before

removal.  However, it executed fuser with the system() call in an insecure

fashion.  A malicious user could construct an environment such that this

provided them a local root shell.  Tmpwatch now uses execle() to run fuser.



4. Solution:



For each RPM for your particular architecture, run:



rpm -Fvh [filename]



where filename is the name of the RPM.



5. Bug IDs fixed (http://bugzilla.redhat.com/bugzilla for more info):



17286 - tmpwatch run from cron allows locale DoS.





6. RPMs required:



Red Hat Linux 6.2:



alpha:

http://updates.redhat.com/6.2/alpha/tmpwatch-2.6.2-1.6.2.alpha.rpm



sparc:

http://updates.redhat.com/6.2/sparc/tmpwatch-2.6.2-1.6.2.sparc.rpm



i386:

http://updates.redhat.com/6.2/i386/tmpwatch-2.6.2-1.6.2.i386.rpm



sources:

http://updates.redhat.com/6.2/SRPMS/tmpwatch-2.6.2-1.6.2.src.rpm



Red Hat Linux 7.0:



i386:

http://updates.redhat.com/7.0/i386/tmpwatch-2.6.2-1.7.i386.rpm



sources:

http://updates.redhat.com/7.0/SRPMS/tmpwatch-2.6.2-1.7.src.rpm



7. Verification:



MD5 sum                           Package Name

--------------------------------------------------------------------------

b8a670944cc54fd39c9eefb79f147ec1  6.2/SRPMS/tmpwatch-2.6.2-1.6.2.src.rpm

39fe4fbf666e5f9a40503134c05046d8  6.2/alpha/tmpwatch-2.6.2-1.6.2.alpha.rpm

84609abc355fde23ce878e4d310766f8  6.2/i386/tmpwatch-2.6.2-1.6.2.i386.rpm

f4625e9bc27af011a614eaa146586917  6.2/sparc/tmpwatch-2.6.2-1.6.2.sparc.rpm

b1a9201c44a5f921209c9b648ba85ada  7.0/SRPMS/tmpwatch-2.6.2-1.7.src.rpm

8acf394469c47a98fcc589dd0d73b98c  7.0/i386/tmpwatch-2.6.2-1.7.i386.rpm



These packages are GPG signed by Red Hat, Inc. for security.  Our key

is available at:

    http://www.redhat.com/corp/contact.html



You can verify each package with the following command:

    rpm --checksig  



If you only wish to verify that each package has not been corrupted or

tampered with, examine only the md5sum with the following command:

    rpm --checksig --nogpg 



8. References:



Thanks go to Internet Security System's X-Force team (xforce@iss.net) for

discovering and documenting the local root exploit.





Copyright(c) 2000 Red Hat, Inc.