58 lines
2.2 KiB
HTML
58 lines
2.2 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
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<HTML>
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<META NAME="GENERATOR" CONTENT="SGML-Tools 1.0.9">
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<TITLE>PATH HOWTO: Security concerns</TITLE>
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<LINK HREF="Path-13.html" REL=next>
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<LINK HREF="Path-11.html" REL=previous>
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<LINK HREF="Path.html#toc12" REL=contents>
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<HR>
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<H2><A NAME="s12">12. Security concerns</A></H2>
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<P>
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<P>The path is sometimes a big security problem. It is a very common way
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to hack into a system using some mistakes in path settings. It is
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easy to make Trojan horse attacks if hacker gets root or other users
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to execute his versions of commands.
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<P>A common mistake in the past (?) was to keep '.' in the root's path.
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Malicious hacker makes program 'ls' in his home directory. If root
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makes
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<P>
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<BLOCKQUOTE><CODE>
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<PRE>
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# cd ~hacker
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# ls
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</PRE>
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</CODE></BLOCKQUOTE>
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<P>he executes ls command of hacker's.
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<P>Indirectly, this same applies to all the programs that are executed as
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root. Any of the important daemon processes should never execute
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anything that some other user can write into. In some systems,
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/usr/local/bin is allowed to contain programs with less strict
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security screening - it is just removed from the path of the root
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user. However, if it is known that some daemon executes 'foo' using
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path '/usr/local/bin/:...', it may be possible to cheat daemon to
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execute '/usr/local/bin/foo' instead of '/bin/foo'. Likely anybody
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who can write to '/usr/local/bin' is able to break into the system.
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<P>It is very important to consider in what order the directories are in
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the path. If /usr/local/bin is before /bin, it is a security risk -
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if it is after, it is not possible to overwrite command /bin/foo with
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some localized modification in /usr/local/bin/foo.
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<P>In Linux it should be remembered that the path evaluation is done in
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the operating system call level. Everywhere where an executable file
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path is given you can give a short name that is searched at least from
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/bin and /usr/bin - likely from many other places as well.
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<P>
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<P>
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