A recent research Alexander “alech” Klink and Julian “zeri” Wälde shows that more than half of Internet is vulnerable to Hashing Denial of service vulnerability. The HDOS vulnerability exploits the hash tables consuming more than 99% of the CPU usage hence causing a Denial of service attack.
The security researchers demonstrated the HDOS vulnerability at 28th Chaos Communication Congress security conference in Berlin, Germany, Earth, Milky Way. The talk was titled as "Efficient Denial of Service Attacks on Web Application Platforms". The reaserch shows that most of the web programming languages including PHP, ASP.NET, Java, Python, Ruby, Apache Tomcat (The list goes on and on) are vulnerable to the HDOS vulnerability
PHP 5, Java, ASP.NET as well as V8 are fully vulnerable to this issue and PHP 4, Python and Ruby are partially vulnerable, depending on version or whether the server running the code is a 32-bit or 64-bit machine.
Hash tables are a commonly used data structure in most programming languages," they explained. "Web application servers or platforms commonly parse attacker-controlled POST form data into hash tables automatically, so that they can be accessed by application developers. If the language does not provide a randomized hash function or the application server does not recognize attacks using multi-collisions, an attacker can degenerate the hash table by sending lots of colliding keys.
The algorithmic complexity of inserting n elements into the table then goes to O(n**2), making it possible to exhaust hours of CPU time using a single HTTP request."
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An ethical hacker is a computer and network expert who attacks a security system on behalf of its owners with a written consent on paper of being authorized, seeking vulnerabilities that a malicious hacker could exploit. To test a security system, ethical hackers use the same methods as their less principled counterparts, but report problems instead of taking advantage of them. Ethical hacking is also known as penetration testing, intrusion testing and red teaming. An ethical hacker is sometimes called a white hat, a term that comes from old Western movies, where the "good guy" wore a white hat and the "bad guy" wore a black hat.
One of the first examples of ethical hackers at work was in the 1970s, when the United States government used groups of experts called red teams to hack its own computer systems. According to Ed Skoudis, Vice President of Security Strategy for Predictive Systems' Global Integrity consulting practice, ethical hacking has continued to grow in an otherwise lackluster IT industry, and is becoming increasingly common outside the government and technology sectors where it began. Many large companies, such as IBM, maintain employee teams of ethical hackers.
In a similar but distinct category, a hacktivist is more of a vigilante: detecting, sometimes reporting (and sometimes exploiting) security vulnerabilities as a form of social activism.