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Definition: A backdoor is a method, often surreptitiously installed, that bypasses normal authentication or security controls to gain remote access to a computer system or encrypted data. It allows an unauthorised user, such as a cybercriminal or state actor, to access a system with ease, often without being detected.

A Backdoor can be inserted into a system through various means, including malicious software, vulnerabilities during design or implementation, or intentionally by insiders. They pose a significant security risk as they provide a hidden point of entry that can be exploited by attackers to gain control, steal sensitive data, conduct surveillance, or cause damage.

To mitigate the threat of backdoors, routine security audits and inspections of the system’s code are necessary, along with maintaining updated software, implementing robust security protocols, and adhering to best-practice software development lifecycles.

Key Characteristics:

  • Bypasses Normal Authentication: Offers a way to access a system without going through standard security procedures.
  • Stealthy: Designed to be concealed and difficult to detect.
  • Remote Exploitation: Backdoors can provide access to systems from anywhere, making them a potent tool for attackers.
  • Potential Insider Origin: Can be established deliberately by developers or other insiders with system access.


  • Real-World Example: The infamous Dual_EC_DRBG cryptographic backdoor allegedly introduced by the NSA which allowed for weakened encryption and easier access to data for those who knew about it.
  • Hypothetical Scenario: A disgruntled employee at a software company deliberately inserts a backdoor into a product’s source code, allowing them to remotely access user data post-deployment.

Related Terms:

  • Exploit: A technique used to take advantage of vulnerabilities in software to gain unauthorised access to systems, which could involve the use of backdoors.
  • Vulnerability: A weakness in a system that can be exploited by a cyber attack, which may include backdoors.
  • Trojan Horse: A type of malware that disguises itself as legitimate software but may carry a backdoor to provide access to the system.

What is the OWASP Top 10: Download our flash cards to find out.

Inside you will find a description of the most common web vulnerabilities.

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