A computer-implemented method for detecting illegitimate out-of-band authentication attempts may include 1) identifying a text message that includes a confirmation code for an out-of-band authentication procedure, 2) detecting an attempt to access the text message, 3) determining that the attempt to access the text message was configured to avoid user participation, and 4) performing, in response to determining that the attempt to access the text message was configured to avoid user participation, a remediation action that addresses an illegitimate out-of-band authentication attempt that includes the attempt to access the text message. Various other methods, systems, and computer-readable media are also disclosed.