Azure AD B2C cryptographic flaw allowing account compromise

Azure Active Directory B2C service (AD B2C) mistakenly implemented RSA encryption using the public part of the key pair instead of the private one.
This cryptographic flaw could have allowed an unauthenticated attacker to craft an OAuth refresh token for any AD B2C user account if they knew their public key.
Moreover, every AD B2C user's public key was recoverable through an unrelated vulnerability (though RSA encryption should not rely on public key secrecy regardless).
An attacker could redeem this …

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