In Eclipse Milo versions 0.6.0 through 1.1.4, username-token processing returns distinguishable errors for invalid RSA PKCS#1 v1.5 padding and other authentication failures, allowing an on-path attacker who captures a victim's `Basic128Rsa15`-encrypted username token to use repeated unauthenticated `ActivateSession` requests as a padding oracle, recover the victim's password, and authenticate with the recovered credentials.

In Eclipse Milo versions 0.6.0 through 1.1.4, username-token processing returns distinguishable errors for invalid RSA PKCS#1 v1.5 padding and other authentication failures, allowing an on-path attacker who captures a victim's `Basic128Rsa15`-encrypted username token to use repeated unauthenticated `ActivateSession` requests as a padding oracle, recover the victim's password, and authenticate with the recovered credentials.