Secure coding standards for Shell Programming Post: 302309562

Sponsored Content

Top Forums Shell Programming and Scripting Secure coding standards for Shell Programming Post 302309562 by lavascript on Wednesday 22nd of April 2009 09:15:06 AM

04-22-2009

Registered User

We just had a case where finding script output files in /tmp or /var/tmp or other world writeable dirs, could be written as symlinks by an unprivileged user to cause harm.

It's not easily exploitable due to the output file having to NOT exist and also the user knowing what name it will be, but it is possible.

e.g

If user1 (normal user) wrote a symlink in /tmp to /etc/passwd

user1# ln -s /tmp/script.out /etc/passwd

Then a script came along running as root and created output or debug or anything to /tmp/script.out then it would overwrite /etc/passwd and obviously cause trouble to the system.

As said the user would need to know what scripts would be ran as root and where to output but people sometimes forget to chmod 750 ot 700 certain scripts.

If therefore check any output file i'm going to create as below :-

Code:

output_security()
{
# Check any file to be used is not a symlink elswhere. 
# If exceptions are needed dont call this function
# This is an e.g so doesn't include checking $@
for FILE in $@
do
   if [ -h ${FILE} ];then
       print "ERROR: File [${FILE}] is a sym link and not a regular file" >&2
       print "Potential Security Risk so exiting" >&2
       exit 2
}

outputfile=/tmp/$(basename $0).out
tmpfile=/tmp/$(basename $0).tmp

output_security "${outputfile} ${tmpfile}"

....blah blah

Last edited by lavascript; 04-22-2009 at 10:28 AM.. Reason: dont want " " around $@ in function

lavascript

View Public Profile for lavascript

Find all posts by lavascript

8 More Discussions You Might Find Interesting

1. UNIX for Dummies Questions & Answers

Unix Coding Standards

Hi, I am looking for some coding standards for Unix Shell Scripting. Can anyone help me out in this? Regards, Himanshu

2. Shell Programming and Scripting

Shell Coding question for any experts out there

Given this one long stream of data (all one line): <TransactionDetail><TransactionHeader><ErrorLogging>YES</ErrorLogging><HistoryLogging>YES</HistoryLogging><ErrorDetection>NO</ErrorD...

3. Shell Programming and Scripting

Coding Standard For Unix Shell Scripting!!!

Is there any site on Coding Standard for Shell Scripting in UNIX. Please help me know!!!!! Thanks Om

4. Shell Programming and Scripting

Unix Shell Scripting Standards

Would anyone have details of pre-existing Unix shell scripting standards. I've been asked to prepare a document outlining standards when writing korn shell scripts & don't really know where to start. Thanks.

5. AIX

AIX and Secure Shell

I just installed 5.3 TL0 on a B50 server. I need to get ssh installed. I tried the links at http://sourceforge.net/projects/openssh-aix] I downloaded openssh_5.2p1_aix53.tar and openssh-4.5_srcpatch.tar. The installation failed. The notes say that this was compiled for TL 8, and mine is...

6. UNIX for Dummies Questions & Answers

GUI via secure shell

Hi i am connected to remote system using putty over ssh-1 version. i can see the command line and able to perform the operations through it. is it possible to have a GUI interface of my login rather than terminal access? do i need to use any client other than putty ? any help is much...

7. Shell Programming and Scripting

Need help in shell script coding

I have a file f1.txt that contains string: f1.txt aaa bbb ccc ... I want to write code to search that each string in file f2.txt(this file contains 1000+line codes). file f2.txt .. .. ....aaa...xyz.. ... ... ...ppp... (dots . can be characters ot blank spaces) If particular...

8. UNIX for Dummies Questions & Answers

Help with understand shell script coding

Good afternoon everyone, I am very new to UNIX shell scripting and I am trying to understand the following code. I know what it does but I need to modify it so it will allow me to pass a file name as *FILENAME* Thank for any guidance offered. if ] ; then match=`expr "$file" :...

LEARN ABOUT DEBIAN

e2tools

E2TOOLS(7)						 Miscellaneous Information Manual						E2TOOLS(7)

NAME

       e2tools -  utilities to manipulate files in an ext2/ext3 filesystem

DESCRIPTION

       E2tools	is  a  simple  set  of	GPL'ed utilities to read, write, and manipulate files in an ext2/ext3 filesystem. These utilities access a
       filesystem directly using the ext2fs library. I wrote these tools in order to copy files into a linux filesystem on a machine that does not
       have  ext2  support.  Of  course, they can also be used on a linux machine to read/write to disk images or floppies without having to mount
       them or have root access.

       Supported functionality:

       e2cp   copy files

       e2mv   move files

       e2rm   remove files

       e2mkdir
	      create directory

       e2ln   create hard links

       e2ls   list files/directories

       e2tail output the last part of a file

       In general, to specify a directory or file on an ext2 filesystem for the e2tools utilities, use the following form:

	      filesystem:directory_path

       The filesystem can be an unmounted partition or a regular file that's been formatted to contain an ext2 filesystem.  In general, if a  com-
       mand takes multiple file names on the command line, if the first one contains an ext2 file specification, the rest of the files are assumed
       to be on the same filesystem until another one is explicitly stated:

	      /tmp/boot.img:/tmp/file1

	      /tmp/file2

	      /tmp/file3

	      /tmp/boot2.img:/tmp/file4

       Files 1-3 are on /tmp/boot.img and the last file is on /tmp/boot2.img

SEE ALSO

       e2cp(1), e2ln(1), e2ls(1), e2mkdir(1), e2mv(1), e2rm(1), e2tail(1).

AUTHOR

       The e2tools were written by Keith Sheffield <sheff@pobox.com>.

       This manual page was written by Lucas Wall <lwall@debian.org>, for the Debian project (but may be used by others).

								   March 2, 2005							E2TOOLS(7)