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1 Mar 2016
Background InformationA group of security researchers discovered that SSLv2 (Secure Sockets Layer protocol version 2.0) is vulnerable to the Bleichenbacher RSA padding oracle attack, which can be used to decrypt RSA cipher text without the knowledge of the matching private RSA key. This can be done by observing responses from a server that has the private key and performs the decryption of attacker-provided cipher texts using that key. The researchers also demonstrated a new cross-protocol attack which allows decryption of SSL/TLS sessions using newer protocol versions - SSLv3 or any current TLS (Transport Layer Security) version (1.0 - 1.2) - using this SSLv2 weakness. This flaw is a SSLv2 protocol issue and affects all implementations of the protocol. Researchers refer to this attack as general DROWN. Additionally, flaws were found in the SSLv2 protocol implementation in the OpenSSL cryptography and SSL/TLS library, which make it possible to perform a more efficient variant of the DROWN attack, referred to as special DROWN. These issues were assigned CVE-2016-0703 and CVE-2016-0704 , and were already recently corrected as part of the fix for CVE-2015-0293 . Further details of this attack can be found in the researchers' paper titled DROWN: Breaking TLS using SSLv2 at https://drownattack.com/ , Impact to systemsA server is vulnerable to the DROWN attack if it enables SSLv2 protocol in addition to SSLv3 or TLSv1.x, and if it uses RSA key exchange cipher suites. Server that does not enable SSLv2 can also be vulnerable if it does not enable SSLv2, but shares its private RSA key with another server. For example, DROWN attack can still be used to decrypt HTTPS sessions to a web server that does not enable SSLv2 if it shares its RSA key with e.g. IMAP server, possibly running on the same host, that does enable SSLv2. Use of weak or export SSLv2 ciphers is required to efficiently perform the attack. SSL/TLS connections using non-RSA key exchange, such as Diffie-Hellman or Elliptic Curve Diffie-Hellman, can not be decrypted using the DROWN attack. What configurations are vulnerable to this attack?
2 Sep 2015
QUOTE Call of Duty Modern Warfare 3 smashes entertainment launch recordsCall of Duty: Modern Warfare 3 sells more than 6.5m copies within 24 hours of its launch, earning an estimated $400m in sales
As a Linux system admin we generally face low disk space issues. By implementing the user and group disk quota on the file system we can resolve the space issue. Quota restricts the users to use only allowed disk and inodes on the particular file system. In this post we will discuss how to enable user & group disk quota on /home File system on CentOS 7 & RHEL 7 Step:1 Add usrquota & grpquota option on /home in /etc/fstab file.[root@linuxtechi ~]# vi /etc/fstab Save & exit the file. In this example I have add user and group quota options on /home Step:2 Remount /home file system via mount command[root@linuxtechi ~]# mount -o remount /home Now recheck the /home file system whether Quota is enable or not. [root@linuxtechi ~]# mount | grep /home Step:3 Create Quota Database Files using quotacheck[root@linuxtechi home]# quotacheck -cugv /home Whereas : -c : create quota file and dont use the existing file -v : verbose ouput -u : user disk quota -g : group disk quota Above Command will create aquota.user & aquota.group files under /home Turn on quota on /home using below command : [root@linuxtechi ~]# quotaon /home/ Step:4 Assign user & group disk quota via edquota commands# edquota -g [root@linuxtechi ~]# edquota -u jack [root@linuxtechi ~]# edquota -g sys_admin As shown above we have two kind of Disk quota limits : soft : It will warn the users if the soft limit of disk quota reached ( size is in KB), in above example for jack user soft limit is 5500 KB ( approx 5.5MB ) hard : It will not allow the users to create new files once the hard limit is reached. ( Size in KB ), in above example hard limit for jack user is 6000 KB ( approx 6 MB ) Note : We can also set the Quota on the basis of the inodes ( i.e numbers of files that the user can create on particular file system). Lets take an example , login as jack user and try to create a file of 8MB. [root@linuxtechi ~]# su - jack As we see above soft & hard limit is exceeded for jack user. Now onwards user jack cant create new files. Step:5 Display Quota report for Users in human readable[root@linuxtechi ~]# repquota -as Step:6 Configure Grace Period for Soft LimitGrace period is the amount of time during which soft limit can can be exceeded, once the grace period reached then soft limit will become the hard limit. Use the edquota command to set Grace period . [root@linuxtechi ~]# edquota -t Source: http://www.linuxtechi.com/enable-user-group-disk-quota-on-centos-7-rhel-7/
1 Sep 2015
NIC(Network Interface Card) bonding is also known as Network bonding. It can be defined as the aggregation or combination of multiple NIC into a single bond interface. Its main purpose is to provide high availability and redundancy. In this article we will learn how to configure nic or netwok bonding in CentOS 7 & RHEL 7. In my case I have two interface cards (enp0s3 & enp0s8) and will form a bond interface (bond0). PrerequisiteIf bonding module is not loaded on your linux box then use the below command to load. If bonding module is not loaded on your linux box then use the below command to load. [root@openstack ~]# modprobe bonding To list the bonding module info, use following command. [root@openstack ~]# modinfo bonding Output will be something like below Step:1 Create Bond Interface FileCreate a bond interface file (ifcfg-bond0) under the folder “/etc/sysconfig/network-scripts/”[root@openstack network-scripts]# vi ifcfg-bond0 Save & exit the file. Specify the IP address, Netmask & bonding modes as per your requirement. In my example i am using mode=5′ which is used to provide fault tolerance and load balancing. Step:2 Edit the NIC interface filesFor ifcfg-enp0s3 [root@openstack ~]# vi /etc/sysconfig/network-scripts/ifcfg-enp0s3 For ifcfg-enp0s8 [root@openstack ~]# cat /etc/sysconfig/network-scripts/ifcfg-enp0s8 Step:3 Restart the Network ServiceBelow command will restart the network service and will bring above changes into the effect.[root@openstack ~]# systemctl restart network.service Step:4 Test & Verify bond interface.Use ifconfig & ip add command to check bond interface along with its slave interfaces.Use following command to view bond interface settings like bonding mode & slave interface. [root@openstack ~]# cat /proc/net/bonding/bond0 Step:5 Fault tolerance testingTo test the fault tolerance we can down one interface and check whether you are still able access the server. [root@openstack ~]# ifdown enp0s8 Source: http://www.linuxtechi.com/configure-nic-bonding-in-centos-7-rhel-7/
5 Feb 2015
QUOTE Call of Duty Modern Warfare 3 smashes entertainment launch recordsCall of Duty: Modern Warfare 3 sells more than 6.5m copies within 24 hours of its launch, earning an estimated $400m in sales
I have had many people come to my blog looking how to install oVirt 3.5 software on the new CentOS 7. Much of this content is the same as my 3.4 post, but I thought I would keep it separate. Below are simple step by step instructions for installing the node and getting it configured for the hosted engine. Installation RequirementsPlease Note: Installing Hosted Engine on CentOS 7 requires oVirt 3.5.1 Please Note: Both the node and engine will be running CentOS 7 (Minimal Installation) Please Note: Ensure the host is fully updated via “yum update” and rebooted before proceeding PrerequisitesDNSEnsure you have set up hostnames for the host and engine. If you do not have a DNS server configured and you are only testing oVirt on a single server, you can use /etc/hosts instead. I have the following: Engine: Hostname: engine.xrsa.net, IP Address: 192.168.122.101/24 Host: Hostname: ovirt01.xrsa.net, IP Address: 192.168.122.100/24 Ensure you have set up NFS mount points for the engine and virtual machines. If you do not have a shared NFS server and you are only testing oVirt, you can configure NFS locally on the host instead.
Verify you can see the correct mount points.
InstallationNTPThis not a requirement, but it is recommended that you keep your servers time in sync:
You may put your own NTP servers in /etc/ntp.conf if required. Once you have verified DNS and NFS, install the required repositories and packages.
We will need an ISO for the hosted engine installation.
Now all the prerequisites are in place, verify DNS and then go through the hosted-engine wizard.
The hosted-engine wizard will give you VNC details so you can connect to the hosted engine virtual machine and install CentOS 7.
Once installed choose option (1) on the hosted-engine wizard, it will wait until you have rebooted the hosted engine virtual machine. The wizard will give you another set of VNC details to connect to if you need it. However, if you configured networking during the install you should be able to SSH instead. Once you have connected to the hosted engine, download the repositories, configure NTP and run through the ovirt-engine wizard. Please make sure the admin password matches up with the password set in the hosted-engine wizard. Please note: Ensure DNS is configured properly so the engine can resolve itself and the host, else the installation will fail! Please note: While in the engine setup wizard below ensure you put a proper ACL for the “NFS export ACL” option. If you do not you will not be able to activate the ISO_DOMAIN later.
Once finished go back to the hosted-engine wizard and finish off the installation by choosing option (1). It will ask you one final time for the hosted engine to be shutdown, wait a few minutes and it will come back up automatically. After around a minute you can verify the state of the hosted engine virtual machine by using the following command:
Data Domain and ISO_Domain SetupBefore you can create virtual machines in oVirt you need to create a Data Domain and ensure the ISO_DOMAIN is attached to the Default cluster. Navigate to https://engine.xrsa.net and login with admin. Create a new Data / NFS Domain by going to “System -> Storage -> New Domain”: You must wait until the NFS01 Data Domain is in an active state. Once activated attach the ISO_DOMAIN to the Default Data Center: Please note: If you are having issues attaching ISO_DOMAIN to the cluster you might have forgot to add a proper ACL on the “NFS export ACL” option during the engine wizard. You can check this as follows:
If everything went as expected you should see both the NFS01 and ISO_DOMAIN in an up and active state: Uploading ISO ImagesThere is no GUI based ISO upload tool during this time, so to upload ISO images you must login to the engine first and run the following commands:
Using oVirtAt this point everything should be up and running for you to start creating virtual machines. For more information please read the oVirt Documentation: http://www.ovirt.org/DocumentationSource: https://xrsa.net/2015/02/04/installing-ovirt-3-5-on-centos-7-hosted-engine/ View the full article
31 Jan 2015
QUOTE Call of Duty Modern Warfare 3 smashes entertainment launch recordsCall of Duty: Modern Warfare 3 sells more than 6.5m copies within 24 hours of its launch, earning an estimated $400m in sales
The funkily-named bug of the week is GHOST. Its official moniker is the less catchy CVE-2015-0235, and it's a vulnerability caused by a buffer overflow in a system library that is used in many, if not most, Linux distributions. A buffer overflow is where you assume, for example, that when you handle a four-byte network number written out as decimal digits, you will never get anything longer than 255.255.255.255. That takes up 15 characters, so you may decide that you'll never need more than 15 bytes of memory. So, if you add a spare byte for luck and allocate 16 bytes, you're bound to have enough space. And then, one day, a malicious user decides to see what happens if he ignores the rules, and uses a network number like, say, 1024.10224.102224.1022224. That network number is nonsense, of course, but your program might not hold out long enough to reject it. Your code will probably crash right away, because the attacker's 25 bytes will overflow your 16 bytes of available memory. GHOST explainedAs it happens, the GHOST vulnerability is connected with network names and numbers. The spooky name comes from the system functions where the vulnerable code was found. They find the computer-friendly network number of a host (e.g. 93.184.216.34) from its human-friendly name (e.g. example.com). In other words, these functions do a DNS (domain name system) lookup for you, so your program doesn't need to deal with the intricacies of the DNS protocol. For example, if you ignore any error checking in your code, you might do this: And you'd see something like this: By the way, even if your program doesn't directly call gethostbyname(), you may end up calling it indirectly as a side-effect of doing something, anything, involving a computer name. For example, if your software looks up email addresses, calls home for updates, retrieves postings from online forums, plays podcasts, or any of a number of perfectly unexceptionable network-related activities, it almost certainly triggers name-to-number lookups at some point. And if those lookups are based on data received from outside, such as a sender's email address in received email headers, then attackers may very well get to choose what data gets passed to your Linux computer's gethostbyname() function. The bugIt turns out that gethostbyname() has a clever feature, where it works out whether you called it with name that is already a network number (digits-dot-digits-dot-digits-dot-digits). In that case, it would be a waste of time to do a DNS lookup, so it doesn't bother. Unfortunately, the code that runs through the name to see if it's really a network number has a buffer overflow, and if you deliberately send a super-long number laid out just right... ...poof – the GHOST strikes! So an attacker may be able to rig up messages or network requests that crash your program; and with a bit (or, more likely, a lot) of trial and error, they might be able to trigger that crash in a way that gives them control over your computer. That's known as a Remote Code Execution (RCE) exploit, similar to the bug recently found in the super-secure Blackphone, though in that case it was a text message that caused the phone's software to trip over itself. What to do?The good news is that this bug doesn't exist on every computer. It actually exists only in some versions of a software module called glibc, short for GNU C library. In fact, most computers in the world don't have glibc installed, because it's not used by default on Windows, OS X, iOS or Android. The bad news is that many, if not most, computers running Linux do use glibc, and may be at risk. In short, therefore, if you have any Linux-based systems, including home firewalls and routers:
Oh, and if you are a programmer, you shouldn't really be using the gethostbyname functions anyway. They were superseded many years ago by the much more flexible and useful function getaddrinfo(), which you should use instead. View the full article |
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