The SolarWinds compromise involved attackers gaining access to the company's software development environment and inserting malicious code into builds for versions 2019.4 HF 5, 2020.2 unpatched, and 2020.2 HF 1 of the company's Orion network management platform. (The list of all affected products is here). The tainted builds were digitally signed and automatically pushed out to about 18,000 customers over a period of several months last year. Only a relatively small number of those organizations are believed to have been actually targeted for subsequent attacks.

The manner in which threat actors gained initial access to SolarWinds' build system environment remains unclear. A SolarWinds update on Feb. 3 described the company as still "exploring several potential theories" about how the threat actors broke in. According to SolarWinds, current evidence suggests that the most likely attack vector was through a credential compromise and/or access through a then zero-day vulnerability in a third-party app.

SolarWinds has also confirmed that an email account belonging to one of its employees was compromised and used to "programmatically access" accounts belonging to other targeted individuals. The attackers used the credentials to eventually gain access to SolarWinds' Orion development environment. The company says its data shows the attackers were in its network conducting reconnaissance for an unknown period of time before they began conducting trial runs of injecting malware into SolarWinds' build system in October 2019.

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