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Using umask
The umask can be used to control the default file permission on newly-created files. The umask command controls the default file and directory creation mode for newly-created files and directories. It is recommended that you make root's umask 077, which will disable read, write, and execute permission for other users, unless explictly changed using chmod.
The umask command can be used to determine the default file creation mode on your system. It is the octal complement of the desired file mode. If files are created without any regard to their permissions settings, a user could inadvertently give read or write permission to someone that should not have this permission.
The umask for the creation of new executable files is calculated as follows:
777 Default Permissions -022 Subtract umask value, for example ----- 755 Allowed Permissions
So in this example we chose 022 as our umask. This shows us that new executables that are created are given mode 755, which means that the owner can read, write, and execute the binary, while members of the group to which the binary belongs, and all others, can only read and execute it.
The umask for the creation of new text files is calculated as follows:
666 Default Permissions -022 Subtract umask mask, for example ----- 644 Allowed Permissions
This example shows us that given the default umask of 666, and subtracting our sample umask value of 022, new text files are created with mode 644, which states that the owner can read and write the file, while members of the group to which the file belongs, and everyone else can only read the new file. Typically umask settings include 022, 027, and 077, which is the most restrictive. Normally the umask is set in /etc/profile, so it applies to all users on the system. The file creation mask must be set while keeping in mind the purpose of the account. Permissions that are too restrictive may cause users to start sharing accounts or passwords, or otherwise compromise security. For example, you may have a line that looks like this:
# Set the user's default umask umask 033
Be sure to make root's umask to at least 022, which will disable write and execute permission for other users, unless explicitly changed using chmod(1).
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LinuxSecurity.com Feature Extras:
Linux File & Directory Permissions Mistakes - 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.
Introduction: Buffer Overflow Vulnerabilities - Buffer overflows are a leading type of security vulnerability. This paper explains what a buffer overflow is, how it can be exploited, and what countermeasures can be taken to prevent the use of buffer overflow vulnerabilities.
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.
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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: New Apache packages fix HTTP request smuggling | ||
8th, September, 2005
Updated package. advisories/debian/debian-new-apache-packages-fix-http-request-smuggling |
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| Debian: New kdelibs packages fix backup file information leak | ||
8th, September, 2005
Updated package. advisories/debian/debian-new-kdelibs-packages-fix-backup-file-information-leak-15398 |
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| Debian: New Apache2 packages fix several vulnerabilities | ||
8th, September, 2005
Updated package. advisories/debian/debian-new-apache2-packages-fix-several-vulnerabilities |
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| Debian: New cvs packages fix insecure temporary files | ||
9th, September, 2005
Updated package. advisories/debian/debian-new-cvs-packages-fix-insecure-temporary-files-45438 |
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| Debian: New mod_ssl packages fix acl restriction bypass | ||
12th, September, 2005
Updated package. advisories/debian/debian-new-modssl-packages-fix-acl-restriction-bypass |
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| Debian: New tdiary packages fix Cross Site Request Forgery | ||
12th, September, 2005
Updated package. advisories/debian/debian-new-tdiary-packages-fix-cross-site-request-forgery |
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| Debian: New squid packages fix several vulnerabilities | ||
13th, September, 2005
Update package. advisories/debian/debian-new-squid-packages-fix-several-vulnerabilities-15114 |
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| Debian: New Mozilla packages fix several vulnerabilities | ||
13th, September, 2005
Updated package. advisories/debian/debian-new-mozilla-packages-fix-several-vulnerabilities-49307 |
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| Debian: New common-lisp-controller packages fix arbitrary code injection | ||
14th, September, 2005
Updated package. advisories/debian/debian-new-common-lisp-controller-packages-fix-arbitrary-code-injection-32460 |
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| Debian: New turqstat packages fix buffer overflow | ||
15th, September, 2005
Updated package. advisories/debian/debian-new-turqstat-packages-fix-buffer-overflow |
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| Debian: New centericq packages fix several vulnerabilities | ||
15th, September, 2005
Updated package. advisories/debian/debian-new-centericq-packages-fix-several-vulnerabilities |
||
| Fedora Core 4 Update: slib-3a1-3.fc4 | ||
8th, September, 2005
*.scm and *.init scripts shipped with slib expect that slib is located directly in /usr/local/lib what's not true. This update fixes this problem. advisories/fedora/fedora-core-4-update-slib-3a1-3fc4-11-41-00-120334 |
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| Fedora Core 4 Update: umb-scheme-3.2-39.fc4 | ||
8th, September, 2005
UMB-scheme package conflicts with the SLIB package by instalation of /usr/share/info/slib.info.gz. This update fixes the issue. advisories/fedora/fedora-core-4-update-umb-scheme-32-39fc4-11-41-00-120335 |
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| Fedora Core 4 Update: psmisc-21.5-5 | ||
8th, September, 2005
Updated package. advisories/fedora/fedora-core-4-update-psmisc-215-5-11-42-00-120336 |
||
| Fedora Core 4 Update: glib2-2.6.6-1 | ||
8th, September, 2005
GLib 2.6.6 fixes several bugs in the GOption cmdline option parser, in the GKeyFile keyfile parser, a possible deadlock with threadpools and several other bugs. advisories/fedora/fedora-core-4-update-glib2-266-1-15-24-00-120340 |
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| Fedora Core 4 Update: gtk2-2.6.10-1 | ||
8th, September, 2005
GTK+ 2.6.10 fixes numerous bugs in the file chooser, the icon view, and some other widgets. See the release announcements at https://www.gtk.org/ for more details. advisories/fedora/fedora-core-4-update-gtk2-2610-1-15-25-00-120341 |
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| Fedora Core 4 Update: file-4.15-fc4.1 | ||
9th, September, 2005
Several bug fixes and new magics. advisories/fedora/fedora-core-4-update-file-415-fc41-02-46-00-120344 |
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| Fedora Core 4 Update: subversion-1.2.3-2.1 | ||
9th, September, 2005
This update includes the latest stable release of Subversion, including a number of bug fixes. advisories/fedora/fedora-core-4-update-subversion-123-21-11-45-00-120346 |
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| Fedora Core 3 Update: unzip-5.51-4.fc3 | ||
9th, September, 2005
This update fixes TOCTOU issue in unzip. advisories/fedora/fedora-core-3-update-unzip-551-4fc3-11-46-00-120347 |
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| Fedora Core 4 Update: util-linux-2.12p-9.10 | ||
9th, September, 2005
Updated package. advisories/fedora/fedora-core-4-update-util-linux-212p-910-15-13-00-120348 |
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| Fedora Core 4 Update: e2fsprogs-1.38-0.FC4.1 | ||
9th, September, 2005
Updated package. advisories/fedora/fedora-core-4-update-e2fsprogs-138-0fc41-15-13-00-120349 |
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| Fedora Core 4 Update: selinux-policy-targeted-1.25.4-10.1 | ||
9th, September, 2005
Updated package. advisories/fedora/fedora-core-4-update-selinux-policy-targeted-1254-101-15-14-00-120350 |
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| Fedora Core 3 Update: e2fsprogs-1.38-0.FC3.1 | ||
9th, September, 2005
Updated package. advisories/fedora/fedora-core-3-update-e2fsprogs-138-0fc31-15-14-00-120351 |
||
| Fedora Core 4 Update: firefox-1.0.6-1.2.fc4 | ||
10th, September, 2005
Updated package. advisories/fedora/fedora-core-4-update-firefox-106-12fc4-00-41-00-120354 |
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| Fedora Core 3 Update: firefox-1.0.6-1.2.fc3 | ||
10th, September, 2005
Updated package. advisories/fedora/fedora-core-3-update-firefox-106-12fc3-00-42-00-120355 |
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| Fedora Core 4 Update: mozilla-1.7.10-1.5.2 | ||
10th, September, 2005
Updated package. advisories/fedora/fedora-core-4-update-mozilla-1710-152-00-42-00-120356 |
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| Fedora Core 3 Update: mozilla-1.7.10-1.3.2 | ||
10th, September, 2005
Updated package. advisories/fedora/fedora-core-3-update-mozilla-1710-132-00-43-00-120357 |
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| Fedora Core 3 Update: vte-0.11.14-3.fc3 | ||
12th, September, 2005
Please report regressions to GNOME Bugzilla. advisories/fedora/fedora-core-3-update-vte-01114-3fc3-11-17-00-120361 |
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| Fedora Core 4 Update: vte-0.11.14-3.fc4 | ||
12th, September, 2005
Please report regressions to GNOME Bugzilla. advisories/fedora/fedora-core-4-update-vte-01114-3fc4-11-18-00-120362 |
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| Fedora Core 4 Update: slib-3a1-4.fc4 | ||
12th, September, 2005
Updated package. advisories/fedora/fedora-core-4-update-slib-3a1-4fc4-12-38-00-120364 |
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| Fedora Core 4 Update: xdelta-1.1.3-17.fc4 | ||
12th, September, 2005
xdelta shipped with FC4 isn't compiled with large file support and uses obsolete glib-1.2 library. The libedsio symbols are missing from the installed libxdelta library. This release introduces xdelta ported to glib-2 and fixes the noted issues. advisories/fedora/fedora-core-4-update-xdelta-113-17fc4-12-39-00-120365 |
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| Fedora Core 3 Update: xdelta-1.1.3-16.fc3 | ||
12th, September, 2005
xdelta shipped with FC3 isn't compiled with large file support and uses obsolete glib-1.2 library. The libedsio symbols are missing from the installed libxdelta library. This release introduces xdelta ported to glib-2 and fixes the noted issues. advisories/fedora/fedora-core-3-update-xdelta-113-16fc3-12-39-00-120366 |
||
| Fedora Core 4 Update: tvtime-1.0.1-0.fc4.1 | ||
12th, September, 2005
Updated package. advisories/fedora/fedora-core-4-update-tvtime-101-0fc41-12-40-00-120367 |
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| Fedora Core 4 Update: evolution-data-server-1.2.3-3.fc4 | ||
12th, September, 2005
Updated package. advisories/fedora/fedora-core-4-update-evolution-data-server-123-3fc4-13-03-00-120368 |
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| Fedora Core 4 Update: openssh-4.2p1-fc4.1 | ||
12th, September, 2005
Updated package. advisories/fedora/fedora-core-4-update-openssh-42p1-fc41-13-32-00-120369 |
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| Fedora Core 4 Update: dhcp-3.0.2-22.FC4 | ||
13th, September, 2005
Updated package. advisories/fedora/fedora-core-4-update-dhcp-302-22fc4-00-01-00-120373 |
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| Fedora Core 3 Update: gnupg-1.2.7-1 | ||
14th, September, 2005
This update upgrades GnuPG from version 1.2.6 to version 1.2.7, fixing bug #139209 (~/.gnupg not created when gpg is first run), among others. advisories/fedora/fedora-core-3-update-gnupg-127-1-17-13-00-120383 |
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| Fedora Core 4 Update: util-linux-2.12p-9.11 | ||
14th, September, 2005
Updated package. advisories/fedora/fedora-core-4-update-util-linux-212p-911-17-17-00-120384 |
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| Fedora Core 3 Update: mc-4.6.1-2.FC3 | ||
14th, September, 2005
Updated package. advisories/fedora/fedora-core-3-update-mc-461-2fc3-17-17-00-120385 |
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| Fedora Core 3 Update: util-linux-2.12a-24.5 | ||
14th, September, 2005
Updated package. advisories/fedora/fedora-core-3-update-util-linux-212a-245-17-22-00-120386 |
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| Fedora Core 4 Update: mc-4.6.1a-0.12.FC4 | ||
14th, September, 2005
Updated package. advisories/fedora/fedora-core-4-update-mc-461a-012fc4-17-23-00-120387 |
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| Fedora Core 4 Update: libwnck-2.10.3-1 | ||
14th, September, 2005
This update upgrades libwnck to version 2.10.3 in order to work well with metacity 2.10.3. This updated package corrects the behavior of workspace switching when minized windows from a different workspace than the current workspace are activated. advisories/fedora/fedora-core-4-update-libwnck-2103-1-18-04-00-120388 |
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| Gentoo: X.Org Heap overflow in pixmap allocation | ||
12th, September, 2005
An integer overflow in pixmap memory allocation potentially allows any X.Org user to execute arbitrary code with elevated privileges. |
||
| Gentoo: Python Heap overflow in the included PCRE library | ||
12th, September, 2005
The "re" Python module is vulnerable to a heap overflow, possibly leading to the execution of arbitrary code. |
||
| RedHat: Moderate: pcre security update | ||
8th, September, 2005
Updated pcre packages are now available to correct a security issue. This update has been rated as having moderate security impact by the Red Hat Security Response Team advisories/red-hat/redhat-moderate-pcre-security-update-RHSA-2007-1065-01 |
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| RedHat: Moderate: exim security update | ||
8th, September, 2005
Updated exim packages that fix a security issue in PCRE and a free space computation on large file system bug are now available for Red Hat Enterprise Linux 4. This update has been rated as having moderate security impact by the Red Hat Security Response Team. advisories/red-hat/redhat-moderate-exim-security-update-40430 |
||
| RedHat: Critical: firefox security update | ||
9th, September, 2005
An updated firefox package that fixes as security bug is now available for Red Hat Enterprise Linux 4. This update has been rated as having critical security impact by the Red Hat Security Response Team. advisories/red-hat/redhat-critical-firefox-security-update-38591 |
||
| RedHat: Critical: mozilla security update | ||
9th, September, 2005
An updated mozilla package that fixes a security bug is now available. This update has been rated as having critical security impact by the Red Hat Security Response Team. advisories/red-hat/redhat-critical-mozilla-security-update-54092 |
||
| RedHat: Important: XFree86 security update | ||
12th, September, 2005
Updated XFree86 packages that fix several integer overflows are now available for Red Hat Enterprise Linux 2.1. This update has been rated as having important security impact by the Red Hat Security Response Team. advisories/red-hat/redhat-important-xfree86-security-update-11213 |
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| RedHat: Important: xorg-x11 security update | ||
13th, September, 2005
Updated X.org packages that fix several integer overflows are now available for Red Hat Enterprise Linux 4. This update has been rated as having important security impact by the Red Hat Security Response Team. advisories/red-hat/redhat-important-xorg-x11-security-update-6165 |
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| RedHat: Important: XFree86 security update | ||
15th, September, 2005
This update has been rated as having important security impact by the Red Hat Security Response Team. advisories/red-hat/redhat-important-xfree86-security-update-11213 |
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| RedHat: Important: squid security update | ||
15th, September, 2005
An updated Squid package that fixes security issues is now available. This update has been rated as having important security impact by the Red Hat Security Response Team. advisories/red-hat/redhat-important-squid-security-update-83322 |
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