Backdoor

A backdoor is a method of covertly bypassing authentication, often in a digital system. A backdoor can be placed intentionally by a party to secretly access the system, or can be the result of a bug or exploit.

There are many types of backdoor.

Backdoor malware

A backdoor malware is a software that, when executed installs a backdoor into the system that executed it.^[1] This is often referred to as a Trojan. These often use an unpatched exploit to gain access to the system.

Proprietary backdoors

A propriatary backdoor is a built-in backdoor; A backdoor that was intentionally placed there.^[1] These backdoors can be used for good or bad purposes. Some may exist for testing purposes. However, if left in the final product, may be susceptible to exploitation. Other built-in backdoors are used by the company for nefarious purposes.

Backdoors can be used to inject spyware in order to collect information on users. ^[1] Backdoors are dangerous as they can be both officially implanted by project maintainers for various reasons or implanted by unofficial code contributors or distributors.

Main article: SecuRam installs backdoor on ProLogic series safe locks

Signal, an encrypted messenger, has threatened to leave Australia to due the Australian Government’s mandate to have access over the contents of Signal’s messages.^[2][3] While this is not an example of a backdoor, this is an example of how governments can demand that platforms implement malicious backdoors.

The XZ Utils backdoor was a code contribution to the XZ Utilities Linux system package that allowed remote code execution through a specific SSH key.^[4] This backdoor was significant as it went against the previously commonly held belief of open source software security through independent code auditing. The code contributor first had built trust with the maintainers by submitting legitimate code initially before implementing the backdoor in a subtle way through multiple layers to avoid suspicion. However this backdoor was discovered by Andres Freund.^[5]