AADSTS is Microsoft Entra ID’s family of error codes for authentication and token-processing failures. The code prefix appears when a sign-in, token exchange, or OAuth flow cannot be completed, and the remaining number identifies the specific failure condition.
These errors matter in cyber security because they expose how an identity system is reacting to a request. In real attacks, adversaries may submit crafted sign-in attempts and compare AADSTS responses to infer whether a username exists, whether a password is valid, or whether a request reached a particular stage of processing. Defenders use the same signals for troubleshooting and detection: repeated AADSTS failures, unusual client IDs, and bursts of similar errors can indicate password probing, automation, or misconfigured apps. Treating error patterns as security telemetry helps catch abuse that never produces a successful login.