What is memcached?

But at first let us consider a small introduction. So memcached is a free and open high-performance distributed system for caching objects in memory. It is a storage of “key-value” type located in the operating memory and designed for small “portions” of arbitrary data (string values, numerical values, not infrequently serialized objects in the form of string values) such as results of queries to DB, results of API calls or generation of pages. In addition, memcached is a fully open development, is assembled and operated under UNIX, Windows, OS X and distributed under an open license. It is used by many popular web projects, for example, LiveJournal, Twitter, Flickr, YouTube, Wikipedia, etc. It is a normal network service with host-base authentication, which is operated in loopback interface on port 11211. memcached daemon supports UDP- and TCP-sockets and provides two different protocols for interaction with itself: text and binary. I suppose that this is all what we are to know about the patient so far.

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Bug Bounty—vulnerability reward programs for vendors—become more and more widespread. And sometimes, vulnerabilities search detects some evidently insecure areas (e.g., self-XSS) the threat of which is hard to prove. But the larger (or even the smarter) is the vendor (e.g., Google), the more willing it is to discuss, to detect the indicated vulnerability and to reward if successful. This article is a collating of complex situations and the ways to prove a threat and to make the Internet more secure.

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As you can remember ( and as a must to remember for each good administrator) it is not a good idea to work as a root user on Linux. In a perfect world you should use it only to configure a server, to install or to update software, by and large, only for purely administrative purposes. The problem is that we live in the real world that is, actually, quite far away from a perfect one. So, the situation is quite common and, generally, because of negligence, wherefore, the Linux users had no choice but to figure out how does their software works. However, if you know how does the system work and understand its safety mechanisms then you will never work as a root user. Anyway, today we are going to review the ways of raising authorities up from the unprivileged user to a root one, unlike the situation with Windows where we were considering the ways of running with administrative privileges. So, let’s start.

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Apache

Let’s start with the configuration of the Indian who gained recognition on many servers on the web. The first setting we select is the one that prevents an attacker from recognizing the version of Apache. To do this, you can use two directives that have to be set to the following values:

ServerSignature Off
ServerTokens Prod

Separate user and group

The second step is to make sure that Apache runs under its own separate user and group. If the same user also manages something else, e.g. DBMS, an attacker who manages to compromise the web server can have access to the database as well.

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One of the few interesting exploits that I could find includes the ability to download the source code of ASPX pages whose address is known in advance and accessible from outside. This vulnerability exists only in SharePoint 2007, and the exploit is quite simple:

http://www.example.com/_layouts/download.aspx?SourceUrl=/Pages/Default.aspx&Source=http://www.example.com/Pages/Default.aspx&FldUrl=

This could be useful, if the website has proprietary code. But you still need to know the address of specific page.

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Now, when everyone is obsessed with encryption, cryptocontainers and other methods of fighting with “software attacks” such seemingly obsolete things like intrusion bugs are regarded as artifacts from James Bond movies rather than a real threat. As a consequence, a network that is physically isolated from the Internet is considered to be almost invulnerable to hackers. Even if the length of the network is many kilometers, and there are no security people to protect many of its components, which are literally accessible to anyone, sometimes just open to anyone, the network is still considered to be absolutely secure. Actually, it is not, as experience has shown.

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Let us try to consider an implementation of any cryptographic algorithm from top downwards. At the first stage a cryptographic algorithm is written in the form of mathematic operators. Here the algorithm is in the environment where only mathematical laws are valid; therefore, researchers verify only the mathematical resistance of the algorithm, or its cryptoresistance. We have a low interest in this step because mathematical operations should be converted into a code. At the code operation stage the critical information about the cipher operation can ooze through holes in the implementation. Buffer overflow, incorrect memory operations, non-documented capabilities and other features of the program environment enable an intruder to find a secret encryption key without using complicated mathematical manipulations. Many researchers stop at this step forgetting that there is at least one more step. Data reflect the real physical state of logical elements rather than an abstract notion whereas computations are physical processes which convert logical elements from one state to another. Consequently, the program execution is a conversion of physical signals, and from this point of view the result of operation of an algorithm is determined by physical laws. Hence the implementation of a cryptographic algorithm can be considered in the mathematical, program and physical environments.

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