Username-Token Padding Oracle in Eclipse Milo

Executive Summary

This vulnerability affects Eclipse Milo versions 0.6.0 through 1.1.4. It involves username-token processing returning different error messages for invalid RSA PKCS#1 v1.5 padding versus other authentication failures. An attacker can exploit this by capturing a victim's encrypted username token and using repeated unauthenticated ActivateSession requests as a padding oracle to recover the victim's password and authenticate with those credentials.

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Detection Guidance

Detecting this vulnerability requires monitoring for distinguishable error responses during username-token authentication. Check logs for inconsistent status codes like Bad_IdentityTokenInvalid versus other errors during ActivateSession requests. Use network traffic analysis tools to inspect OPC UA protocol exchanges for repeated failed authentication attempts with varying padding errors.

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Impact Analysis

If you use affected Eclipse Milo versions, an attacker could intercept encrypted credentials, decrypt your password, and gain unauthorized access to systems using those credentials. This could lead to data breaches, unauthorized operations, or full system compromise depending on the privileges of the compromised account.

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Compliance Impact

This vulnerability could lead to unauthorized access to sensitive data, violating confidentiality requirements in GDPR and HIPAA. Organizations using affected versions may face compliance violations, potential data breaches, and associated legal penalties if exploited.

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Mitigation Strategies

Upgrade Eclipse Milo to versions beyond 1.1.4 where the fix has been applied. If upgrading is not immediately possible, implement strict rate limiting on ActivateSession requests and ensure all authentication failures return uniform error messages. Disable Basic128Rsa15 encryption if not required.

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