Downgrade Attack
Adversaries may downgrade or use a version of system features that may be outdated, vulnerable, and/or does not support updated security controls. Downgrade attacks typically take advantage of a system’s backward compatibility to force it into less secure modes of operation. Adversaries may downgrade and use various less-secure versions of features of a system, such as Command and Scripting Interpreters or even network protocols that can be abused to enable Adversary-in-the-Middle or Network Sniffing. For example, PowerShell versions 5+ includes Script Block Logging (SBL) which can record executed script content. However, adversaries may attempt to execute a previous version of PowerShell that does not support SBL with the intent to Impair Defenses while running malicious scripts that may have otherwise been detected. Adversaries may similarly target network traffic to downgrade from an encrypted HTTPS connection to an unsecured HTTP connection that exposes network data in clear text.
Open detection, hunting, mitigation, and evidence workspace
Detection logic
Monitor for commands or other activity that may be indicative of attempts to abuse older or deprecated technologies (ex: powershell –v 2). Also monitor for other abnormal events, such as execution of and/or processes spawning from a version of a tool that is not expected in the environment. Monitor for Windows event ID (EID) 400, specifically the EngineVersion field which shows the version of PowerShell running and may highlight a malicious downgrade attack. Monitor network data to detect cases where HTTP is used instead of HTTPS.