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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 ht packages fix arbitrary code execution | ||
8th, July, 2005
Several problems have been discovered in ht, a viewer, editor and analyser for various executables, that may lead to the execution of arbitrary code. advisories/debian/debian-new-ht-packages-fix-arbitrary-code-execution |
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| Debian: New fuse packages fix information disclosure | ||
8th, July, 2005
Sven Tantau discovered a security problem in fuse, a filesystem in userspace, that can be exploited by malicious local users to disclose potentially sensitive information. advisories/debian/debian-new-fuse-packages-fix-information-disclosure |
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| Debian: New drupal package fixes multiple vulnerabilities | ||
9th, July, 2005
Two input validation errors were discovered in drupal and its bundled xmlrpc module. These errors can lead to the execution of arbitrary commands on the web server running drupal. advisories/debian/debian-new-drupal-package-fixes-multiple-vulnerabilities |
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| Debian: New egroupware packages fix remote command execution | ||
10th, July, 2005
A vulnerability has been identified in the xmlrpc library included in the egroupware package. This vulnerability could lead to the execution of arbitrary commands on the server running egroupware. advisories/debian/debian-new-egroupware-packages-fix-remote-command-execution |
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| Debian: New ettercap packages fix arbitrary code execution | ||
10th, July, 2005
A vulnerability was discovered in the ettercap package which could allow a remote attacker to execute arbitrary code on the system running ettercap. advisories/debian/debian-new-ettercap-packages-fix-arbitrary-code-execution |
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| Debian: New dhcpcd packages fix denial of service | ||
11th, July, 2005
dhcpcd, a DHCP client for automatically configuring IPv4 networking, can be tricked into reading past the end of the supplied DHCP buffer which could lead to the daemon crashing. advisories/debian/debian-new-dhcpcd-packages-fix-denial-of-service |
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| Debian: New ruby1.8 packages fix arbitrary command execution | ||
11th, July, 2005
A vulnerability has been discovered in ruby1.8 that could allow arbitrary command execution on a server running the ruby xmlrpc server. advisories/debian/debian-new-ruby18-packages-fix-arbitrary-command-execution |
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| Debian: New squid packages fix IP spoofing vulnerability | ||
11th, July, 2005
The upstream developers have discovered a bug in the DNS lookup code of Squid, the popular WWW proxy cache. advisories/debian/debian-new-squid-packages-fix-ip-spoofing-vulnerability |
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| Debian: New gzip packages fix several vulnerabilities | ||
11th, July, 2005
Two problems have been discovered in gzip, the GNU compression utility. advisories/debian/debian-new-gzip-packages-fix-several-vulnerabilities |
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| Debian: New gedit packages fix denial of service | ||
12th, July, 2005
A format string vulnerability has been discovered in gedit, a light-weight text editor for GNOME, that may allow attackers to cause a denial of service (application crash) via a binary file with format string specifiers in the filename. advisories/debian/debian-new-gedit-packages-fix-denial-of-service |
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| Debian: centericq 4.20.0 | ||
13th, July, 2005
Eric Romang discovered that centericq, a text-mode multi-protocol instant messenger client, creates some temporary files with predictable filenames and is hence vulnerable to symlink attacks by local attackers. advisories/debian/debian-centericq-4200 |
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| Debian: New tiff packages fix arbitrary code execution | ||
13th, July, 2005
Frank Warmerdam discovered a stack-based buffer overflow in libtiff, the Tag Image File Format library for processing TIFF graphics files that can lead to the executionof arbitrary code via malformed TIFF files. advisories/debian/debian-new-tiff-packages-fix-arbitrary-code-execution-35015 |
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| Debian: New squirrelmail packages fix several vulnerabilities | ||
13th, July, 2005
Several vulnerabilities have been discovered in Squirrelmail, a commonly used webmail system. advisories/debian/debian-new-squirrelmail-packages-fix-several-vulnerabilities-63440 |
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| Debian: New packages fix remote command execution in phpgroupware | ||
13th, July, 2005
A vulnerability had been identified in the xmlrpc library included with phpgroupware, a web-based application including email, calendar and other groupware functionality. This vulnerability could lead to the execution of arbitrary commands on the server running phpgroupware. advisories/debian/debian-new-packages-fix-remote-command-execution-in-phpgroupware |
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| Fedora | ||
| Fedora Core 4 Update: kdegraphics-3.4.1-0.fc4.2 | ||
11th, July, 2005
The new package fixes the rendering problem in kdvi. advisories/fedora/fedora-core-4-update-kdegraphics-341-0fc42-13-06-00-119552 |
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| Fedora Core 4 Update: dlm-kernel-2.6.11.5-20050601.152643.FC4.9 | ||
11th, July, 2005
Update for latest FC4 kernel. advisories/fedora/fedora-core-4-update-dlm-kernel-26115-20050601152643fc49-15-35-00-119554 |
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| Fedora Core 4 Update: gnbd-kernel-2.6.11.2-20050420.133124.FC4.42 | ||
11th, July, 2005
Updated for latest kernel. advisories/fedora/fedora-core-4-update-gnbd-kernel-26112-20050420133124fc442-15-52-00-119555 |
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| Fedora Core 4 Update: cman-kernel-2.6.11.5-20050601.152643.FC4.8 | ||
11th, July, 2005
Update for latest kernel. advisories/fedora/fedora-core-4-update-cman-kernel-26115-20050601152643fc48-15-56-00-119556 |
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| Fedora Core 4 Update: GFS-kernel-2.6.11.8-20050601.152643.FC4.1 | ||
11th, July, 2005
Update for latest kernel. advisories/fedora/fedora-core-4-update-gfs-kernel-26118-20050601152643fc41-71065-16-13-00-119558 |
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| Fedora Core 4 Update: GFS-kernel-2.6.11.8-20050601.152643.FC4.1 | ||
11th, July, 2005
Update for latest kernel. advisories/fedora/fedora-core-4-update-gfs-kernel-26118-20050601152643fc41-71065-16-13-00-119558 |
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| Fedora Core 4 Update: procps-3.2.5-6.3 | ||
11th, July, 2005
Package updated. advisories/fedora/fedora-core-4-update-procps-325-63-16-30-00-119559 |
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| Fedora Core 3 Update: procps-3.2.3-5.3 | ||
11th, July, 2005
Package updated. advisories/fedora/fedora-core-3-update-procps-323-53-16-51-00-119560 |
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| Fedora Core 4 Update: libwnck-2.10.0-4.fc4 | ||
11th, July, 2005
Package updated. advisories/fedora/fedora-core-4-update-libwnck-2100-4fc4-23-31-00-119561 |
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| Fedora Core 4 Update: metacity-2.10.0-2.fc4 | ||
11th, July, 2005
Package updated. advisories/fedora/fedora-core-4-update-metacity-2100-2fc4-23-32-00-119562 |
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| Fedora Core 4 Update: gaim-1.4.0-4.fc4 | ||
11th, July, 2005
Package updated. advisories/fedora/fedora-core-4-update-gaim-140-4fc4-23-33-00-119563 |
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| Fedora Core 3 Update: gaim-1.4.0-4.fc3 | ||
11th, July, 2005
Package updated. advisories/fedora/fedora-core-3-update-gaim-140-4fc3-23-41-00-119564 |
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| Fedora Core 4 Update: audit-0.9.15-1.FC4 | ||
12th, July, 2005
This update adds interpretive mode for ausearch utility to make results easier to read, sighup support, big performance improvements, lots of bug fixes, more documentation in man pages, and more syslog information for failure conditions. advisories/fedora/fedora-core-4-update-audit-0915-1fc4-12-16-00-119570 |
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| Fedora Core 4 Update: libxml2-2.6.20-1.FC4 | ||
12th, July, 2005
This update fixes 162837 about XPath and XSLT problems with 2.6.19 as well as a number of bug fixes upstream, especially on W3C XML Schemas conformance. advisories/fedora/fedora-core-4-update-libxml2-2620-1fc4-12-28-00-119571 |
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| Fedora Core 3 Update: dhcp-3.0.1-44_FC3 | ||
12th, July, 2005
Updated package released. advisories/fedora/fedora-core-3-update-dhcp-301-44fc3-14-22-00-119572 |
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| Fedora Core 4 Update: dhcp-3.0.2-14.FC4 | ||
12th, July, 2005
Updated package released. advisories/fedora/fedora-core-4-update-dhcp-302-14fc4-14-34-00-119573 |
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| Fedora Core 3 Update: lam-7.1.1-6.FC3 | ||
12th, July, 2005
Updated package released. advisories/fedora/fedora-core-3-update-lam-711-6fc3-14-42-00-119576 |
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| Fedora Core 4 Update: lam-7.1.1-6.FC4 | ||
12th, July, 2005
Updated package released. advisories/fedora/fedora-core-4-update-lam-711-6fc4-14-55-00-119577 |
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| Fedora Core 3 Update: vixie-cron-4.1-36.FC3 | ||
12th, July, 2005
Updated package released. advisories/fedora/fedora-core-3-update-vixie-cron-41-36fc3-15-13-00-119579 |
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| Fedora Core 4 Update: vixie-cron-4.1-36.FC4 | ||
12th, July, 2005
Updated package released. advisories/fedora/fedora-core-4-update-vixie-cron-41-36fc4-15-26-00-119580 |
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| Fedora Core 3 Update: krb5-1.3.6-7 | ||
12th, July, 2005
A double-free flaw was found in the krb5_recvauth() routine which may be triggered by a remote unauthenticated attacker. Fedora Core 3 contains checks within glibc that detect double-free flaws. Therefore, on Fedora Core 3, successful exploitation of this issue can only lead to a denial of service (KDC crash). advisories/fedora/fedora-core-3-update-krb5-136-7-15-42-00-119581 |
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| Fedora Core 4 Update: krb5-1.4.1-5 | ||
12th, July, 2005
A double-free flaw was found in the krb5_recvauth() routine which may be triggered by a remote unauthenticated attacker. Fedora Core 4 contains checks within glibc that detect double-free flaws. Therefore, on Fedora Core 4, successful exploitation of this issue can only lead to a denial of service (KDC crash). advisories/fedora/fedora-core-4-update-krb5-141-5-15-47-00-119582 |
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| Fedora Core 4 Update: net-snmp-5.2.1.2-fc4.1 | ||
13th, July, 2005
A security vulnerability has been found in Net-SNMP releases that could allow a denial of service attack against Net-SNMP agent"s which have opened a stream based protocol (EG, TCP but not UDP; it should be noted that Net-SNMP does not by default open a TCP port). advisories/fedora/fedora-core-4-update-net-snmp-5212-fc41-12-03-00-119591 |
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| Fedora Core 3 Update: net-snmp-5.2.1.2-FC3.1 | ||
13th, July, 2005
Fixes DoS bug (#162908). advisories/fedora/fedora-core-3-update-net-snmp-5212-fc31-13-04-00-119592 |
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| Fedora Core 4 Update: selinux-policy-targeted-1.25.1-9 | ||
13th, July, 2005
Fix saslauthd. advisories/fedora/fedora-core-4-update-selinux-policy-targeted-1251-9-13-22-00-119593 |
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| Fedora Core 3 Update: bind-9.2.5-2 | ||
13th, July, 2005
New package released. advisories/fedora/fedora-core-3-update-bind-925-2-14-04-00-119595 |
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| Fedora Core 4 Update: bind-9.3.1-6.FC4 | ||
13th, July, 2005
New package released. advisories/fedora/fedora-core-4-update-bind-931-6fc4-14-25-00-119596 |
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| Fedora Core 4 Update: rpm-4.4.1-22 | ||
13th, July, 2005
This update corrects security problem CAN-2005-2096, a zlib fix. advisories/fedora/fedora-core-4-update-rpm-441-22-14-34-00-119597 |
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| Fedora Core 4 Update: openssh-4.1p1-3.1 | ||
13th, July, 2005
This update rebases openssh to 4.1p1 upstream. This upstream release is only a bug fix release so the changes should be minimal. Also /etc/nologin processing has been changed so it is not done twice. advisories/fedora/fedora-core-4-update-openssh-41p1-31-15-28-00-119599 |
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| Fedora Core 4 Update: pam-0.79-9.1 | ||
13th, July, 2005
This update fixes a regression in XAUTHORITY handling and updates auditing support. It requires audit-libs update due to changes in its API. advisories/fedora/fedora-core-4-update-pam-079-91-16-15-00-119600 |
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| Gentoo | ||
| Gentoo: phpWebSite Multiple vulnerabilities | ||
10th, July, 2005
phpWebSite is vulnerable to the remote execution of arbitrary PHP script code and to other, yet undisclosed, vulnerabilities. |
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| Gentoo: phpGroupWare, eGroupWare PHP script injection vulnerability | ||
10th, July, 2005
phpGroupWare and eGroupWare include an XML-RPC implementation which allows remote attackers to execute arbitrary PHP script commands. |
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| Gentoo: Adobe Acrobat Reader Buffer overflow vulnerability | ||
11th, July, 2005
Adobe Acrobat Reader is vulnerable to a buffer overflow that could lead to remote execution of arbitrary code. |
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| Gentoo: Ruby Arbitrary command execution through XML-RPC | ||
11th, July, 2005
A vulnerability in XMLRPC.iPIMethods allows remote attackers to execute arbitrary commands. |
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| Gentoo: MIT Kerberos 5 Multiple vulnerabilities | ||
12th, July, 2005
MIT Kerberos 5 is vulnerable to a Denial of Service attack and remote execution of arbitrary code, possibly leading to the compromise of the entire Kerberos realm. |
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| Gentoo: Bugzilla Unauthorized access and information | ||
13th, July, 2005
Multiple vulnerabilities in Bugzilla could allow remote users to modify bug flags or gain sensitive information. |
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| Gentoo: pam_ldap and nss_ldap Plain text authentication | ||
14th, July, 2005
The pam_ldap and nss_ldap modules fail to restart TLS when following a referral, possibly leading to credentials being sent in plain text. |
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| Gentoo: Mozilla Firefox Multiple Vulnerabilities | ||
15th, July, 2005
Several vulnerabilities in Mozilla Firefox allow attacks ranging from execution of script code with elevated privileges to information leak. |
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| Red Hat | ||
| RedHat: Critical: Adobe Acrobat Reader security update | ||
8th, July, 2005
Updated acroread packages that fix a security issue are now available. This update has been rated as having critical security impact by the Red Hat Security Response Team. advisories/red-hat/redhat-critical-adobe-acrobat-reader-security-update-90817 |
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| RedHat: Critical: krb5 security update | ||
12th, July, 2005
Updated krb5 packages which fix multiple security issues are now available for Red Hat Enterprise Linux 2.1 and 3. This update has been rated as having critical security impact by the Red Hat Security Response Team. advisories/red-hat/redhat-critical-krb5-security-update-50912 |
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| RedHat: Important: krb5 security update | ||
12th, July, 2005
Updated krb5 packages that fix multiple security issues 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-krb5-security-update-66067 |
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| RedHat: cups security update | ||
14th, July, 2005
Updated CUPS packages that fix a security issue are now available for Red Hat Enterprise Linux 3. This update has been rated as having moderate security impact by the Red Hat Security Response Team. advisories/red-hat/redhat-cups-security-update-RHSA-2005-571-01 |
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