I am faced with a daunting task: write something useful about server security in 1,800 words or less. Entire books are devoted to the subject, though few could be considered anywhere near comprehensive. It is an issue which I elected to write about, and one that I view as the most important, yet least understood if not an outright neglected aspect of doing business on the Internet.
The purpose of this article is to expand a few horizons, to challenge folks with minimal security related experience to come up with ways to better protect themselves. The standard practice of downloading and installing 3rd party scripts for protection is woefully inefficient, and has proven to oftentimes be more harmful than helpful.
Without wasting further precious space, let’s begin.
If /etc/passwd flew out of your webserver 5 minutes ago, would you know? What if outbound traffic on your OpenVZ host node suddenly increased by 5000%? Would you know if your shared hosting server started listening on TCP port 4444? If a new uid 0 user was added? A new ssh key was authorized?
If you answered "No" to most of those questions, it may be time to rethink your perspective on information security.
What is information security?
Information security is traditionally said to be comprised of 3 attributes: confidentiality, integrity, and availability - or CIA.
Has an unauthorized individual viewed /etc/shadow? Confidentiality has been breached.
Has a malicious user added a uid 0 account to /etc/passwd? The integrity of the file has been degraded. Has someone found a way to kill -9 all sshd processes? Service availability has been impacted.
There are many ways in which those 3 attributes can be compromised. You can decide which attribute(s) to apply to each:
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Physical access (someone steals your servers) Insider access (a rogue employee installs a backdoor on a server)
Social engineering (helpdesk staff at a datacenter provide access to a customer's server without sufficiently verifying the identity of the requester) Trojaned software (realistic looking but backdoored installation media, software repository compromises) Trojaned hardware (network devices with default & unchangeable accounts, BIOS chips with embedded rootkits) Misconfigurations (anonymous FTP access, open mail relay, NFS mount exporting sensitive data to the world) Software bugs (remote command execution, SQL injection) External data leak (posting sensitive information publicly) Unsafe practices (password reuse, running chmod on user controlled data as a privileged user, running sshd on a port above 1024)
Denial of service attacks (protocol weaknesses, the classic WinNuke, bandwidth consumption)
There are seemingly limitless ways in which information security can be compromised. A malicious individual only needs to find one way in order to cause harm to your Internet presence.
There are at least two distinct types of approaches to information security: proactive, and reactive. They are most effective when combined.
A proactive approach involves taking action to prevent or minimize the effects of attacks. For example, if you run a grsecurity based kernel, you are being proactive. Disabling unnecessary services is another proactive approach, as is preventing unnecessary kernel modules from being loaded. Auditing code for bugs is yet another example.
By comparison, a reactive approach is waiting for something undesirable to occur, and addressing the issue once it has been detected (assuming the problem is detected at all). For example, you know that popular php based blogging software has been backdoored recently, and instead of working to find
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