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Linux File & Directory Permissions Mistakes
By: Pax Dickinson
Greetings, gentle reader, and welcome to linuxsecurity.com and our new recurring series of articles on security related mistakes and how to avoid them. I'm your host, Pax Dickinson, and today we'll be reviewing basic Linux file and directory permissions and how to avoid some common pitfalls in their use, in this episode of Hacks From Pax.
One common mistake Linux administrators make is having file and directory permissions that are far too liberal and allow access beyond that which is needed for proper system operations. A full explanation of unix file permissions is beyond the scope of this article, so I'll assume you are familiar with the usage of such tools as chmod, chown, and chgrp. If you'd like a refresher, one is available right here on linuxsecurity.com.
I've witnessed systems administrators whose response to a user complaining about being denied access to a given file is to chmod 777 the file (or entire directory tree) in question. This is an absolutely disastrous security practice, the administrator has just granted write access to the file to any user on the system. Any compromised service will allow an attacker to modify the file, which could result in further access depending on the file in question. For example, an attacker gaining write access to a script that is occasionally run by root can parlay this seemingly minor security hole into full root access for himself.
- Never make files world-writable. Most files do not need to be world readable
either.
- You can search for world-writable files under your current directory by issuing the following command: find . -perm -2 -print
A related mistake is in the misuse of suid root binaries. These are programs which can be launched by a user but run with all the privileges of root. These programs are needed to perform tasks such as changing a user's password, since that requires a write to the system's password file which normally cannot be modified by anyone but root. A flaw that allows an attacker to gain a shell prompt in such a program can give an attacker root access to the system. These binaries should be carefully limited and must be kept up to date with appropriate security patches to minimize their risk. A common backdoor installed by successful attackers is a copy of /bin/sh set suid root. This can be run by any user on the system, without a password, and will result in full root access.
Read Complete Article:
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LinuxSecurity.com Feature Extras:
Getting to Know Linux Security: File Permissions - Welcome to the first tutorial in the 'Getting to Know Linux Security' series. The topic explored is Linux file permissions. It offers an easy to follow explanation of how to read permissions, and how to set them using chmod. This guide is intended for users new to Linux security, therefore very simple. If the feedback is good, I'll consider creating more complex guides for advanced users. Please let us know what you think and how these can be improved.
The Tao of Network Security Monitoring: Beyond Intrusion Detection - To be honest, this was one of the best books that I've read on network security. Others books often dive so deeply into technical discussions, they fail to provide any relevance to network engineers/administrators working in a corporate environment. Budgets, deadlines, and flexibility are issues that we must all address. The Tao of Network Security Monitoring is presented in such a way that all of these are still relevant.
Encrypting Shell Scripts - Do you have scripts that contain sensitive information like passwords and you pretty much depend on file permissions to keep it secure? If so, then that type of security is good provided you keep your system secure and some user doesn't have a "ps -ef" loop running in an attempt to capture that sensitive info (though some applications mask passwords in "ps" output).
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Thank you for reading the LinuxSecurity.com weekly security newsletter. The purpose of this document is to provide our readers with a quick summary of each week's most relevant Linux security headline.
| Debian | ||
| Debian: New crip packages fix insecure temporary files | ||
| 30th, June, 2005
Updated package. advisories/debian/debian-new-crip-packages-fix-insecure-temporary-files |
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| Fedora | ||
| Fedora Core 4 Update: NetworkManager-0.4-18.FC4 | ||
| 24th, June, 2005
This update to NetworkManager includes a number of enhancements. advisories/fedora/fedora-core-4-update-networkmanager-04-18fc4-12-00-00-119413 |
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| Fedora Core 3 Update: kernel-2.6.11-1.35_FC3 | ||
| 24th, June, 2005
Updated package. advisories/fedora/fedora-core-3-update-kernel-2611-135fc3-13-25-00-119414 |
||
| Fedora Core 4 Update: HelixPlayer-1.0.5-1.fc4.2 | ||
| 27th, June, 2005
Updated package. advisories/fedora/fedora-core-4-update-helixplayer-105-1fc42-00-01-00-119417 |
||
| Fedora Core 3 Update: HelixPlayer-1.0.5-0.fc3.2 | ||
| 27th, June, 2005
Updated package. advisories/fedora/fedora-core-3-update-helixplayer-105-0fc32-00-01-00-119418 |
||
| Fedora Core 3 Update: gedit-2.8.1-2.fc3.1 | ||
| 27th, June, 2005
An updated gedit package that fixes a file name format string vulnerability is now available. advisories/fedora/fedora-core-3-update-gedit-281-2fc31-00-02-00-119419 |
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| Fedora Core 4 Update: gedit-2.10.2-4 | ||
| 27th, June, 2005
An updated gedit package that fixes a file name format string vulnerability is now available. advisories/fedora/fedora-core-4-update-gedit-2102-4-00-03-00-119420 |
||
| Fedora Core 3 Update: gzip-1.3.3-15.fc3 | ||
| 27th, June, 2005
In this gzip update there are fixed three small security problems. advisories/fedora/fedora-core-3-update-gzip-133-15fc3-10-53-00-119423 |
||
| Fedora Core 3 Update: selinux-policy-targeted-1.17.30-3.13 | ||
| 27th, June, 2005
Updated package. advisories/fedora/fedora-core-3-update-selinux-policy-targeted-11730-313-10-53-00-119424 |
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| Fedora Core 4 Update: gnome-panel-2.10.1-10.1 | ||
| 28th, June, 2005
Updated package. advisories/fedora/fedora-core-4-update-gnome-panel-2101-101-10-14-00-119429 |
||
| Fedora Core 3 Update: openssh-3.9p1-8.0.2 | ||
| 28th, June, 2005
This is a bug fix update fixing two bugs in ssh client and server code.. advisories/fedora/fedora-core-3-update-openssh-39p1-802-13-31-00-119431 |
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| Fedora Core 4 Update: libwpd-0.8.2-1.fc4 | ||
| 29th, June, 2005
Better handle broken wordperfect documents advisories/fedora/fedora-core-4-update-libwpd-082-1fc4-12-23-00-119437 |
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| Fedora Core 4 Update: openoffice.org-1.9.112-1.1.0.fc4 | ||
| 29th, June, 2005
fix a raft of i18n issues advisories/fedora/fedora-core-4-update-openofficeorg-19112-110fc4-12-24-00-119438 |
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| Fedora Core 3 Update: openssh-3.9p1-8.0.2 (corrected) | ||
| 29th, June, 2005
This is a bug fix update fixing two bugs in ssh client and server code. advisories/fedora/fedora-core-3-update-openssh-39p1-802-corrected-12-25-00-119439 |
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| Fedora Core 3 Update: selinux-policy-targeted-1.17.30-3.15 | ||
| 29th, June, 2005
Updated package. advisories/fedora/fedora-core-3-update-selinux-policy-targeted-11730-315-13-08-00-119440 |
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| Fedora Core 4 Update: selinux-policy-targeted-1.23.18-17 | ||
| 29th, June, 2005
Updated package. advisories/fedora/fedora-core-4-update-selinux-policy-targeted-12318-17-13-53-00-119441 |
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| Fedora Core 3 Update: binutils-2.15.92.0.2-5.1 | ||
| 29th, June, 2005
Updated package. advisories/fedora/fedora-core-3-update-binutils-2159202-51-15-52-00-119442 |
||
| Fedora Core 4 Update: binutils-2.15.94.0.2.2-2.1 | ||
| 29th, June, 2005
Updated package. advisories/fedora/fedora-core-4-update-binutils-21594022-21-15-52-00-119443 |
||
| Fedora Core 4 Update: totem-1.0.4-1 | ||
| 29th, June, 2005
Updated package. advisories/fedora/fedora-core-4-update-totem-104-1-21-39-00-119444 |
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| Fedora Core 4 Update: rgmanager-1.9.34-5 | ||
| 29th, June, 2005
Updated upstream sources. advisories/fedora/fedora-core-4-update-rgmanager-1934-5-21-40-00-119445 |
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| Fedora Core 4 Update: magma-plugins-1.0.0-2 | ||
| 29th, June, 2005
Updated upstream sources. advisories/fedora/fedora-core-4-update-magma-plugins-100-2-21-41-00-119446 |
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| Fedora Core 4 Update: iddev-2.0.0-1 | ||
| 29th, June, 2005
Updated upstream sources. advisories/fedora/fedora-core-4-update-iddev-200-1-21-41-00-119447 |
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| Fedora Core 4 Update: magma-1.0.0-1 | ||
| 29th, June, 2005
Updated upstream sources. advisories/fedora/fedora-core-4-update-magma-100-1-21-42-00-119448 |
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| Fedora Core 4 Update: gulm-1.0.0-2 | ||
| 29th, June, 2005
Updated upstream sources. advisories/fedora/fedora-core-4-update-gulm-100-2-21-43-00-119449 |
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| Fedora Core 4 Update: fence-1.32.1-1 | ||
| 29th, June, 2005
Updated upstream sources. advisories/fedora/fedora-core-4-update-fence-1321-1-21-43-00-119450 |
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| Fedora Core 4 Update: dlm-1.0.0-3 | ||
| 29th, June, 2005
Updated upstream sources. advisories/fedora/fedora-core-4-update-dlm-100-3-21-44-00-119451 |
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| Fedora Core 4 Update: cman-1.0.0-1 | ||
| 29th, June, 2005
Updated upstream sources. advisories/fedora/fedora-core-4-update-cman-100-1-21-45-00-119452 |
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| Fedora Core 4 Update: ccs-1.0.0-1 | ||
| 29th, June, 2005
Updated upstream sources. advisories/fedora/fedora-core-4-update-ccs-100-1-21-45-00-119453 |
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| Fedora Core 4 Update: GFS-6.1.0-3 | ||
| 29th, June, 2005
Updated upstream sources. advisories/fedora/fedora-core-4-update-gfs-610-3-21-46-00-119454 |
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| Fedora Core 4 Update: mod_perl-2.0.1-1.fc4 | ||
| 29th, June, 2005
So FC4 will no longer depend on a pre-release... advisories/fedora/fedora-core-4-update-modperl-201-1fc4-21-47-00-119455 |
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| Gentoo | ||
| Gentoo: Clam AntiVirus Denial of Service vulnerability | ||
| 27th, June, 2005
Clam AntiVirus is vulnerable to a Denial of Service attack when processing certain Quantum archives. |
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| Gentoo: Heimdal Buffer overflow vulnerabilities | ||
| 29th, June, 2005
Multiple buffer overflow vulnerabilities in Heimdal's telnetd server could allow the execution of arbitrary code. |
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| Red Hat | ||
| RedHat: Moderate: sudo security update | ||
| 29th, June, 2005
An updated sudo package is available that fixes a race condition in sudo's pathname validation. This update has been rated as having moderate security impact by the Red Hat Security Response Team. advisories/red-hat/redhat-moderate-sudo-security-update-RHSA-2009-0267-01 |
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