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CVE-2016-4028: An issue was discovered in Open-Xchange OX Guard before 2.4.0-rev8.

An issue was discovered in Open-Xchange OX Guard before 2.4.0-rev8. OX Guard uses an authentication token to identify and transfer guest users' credentials. The OX Guard API acts as a padding oracle by responding with different error codes depending on whether the provided token matches the encryption padding. In combination with AES-CBC, this allows attackers to guess the correct padding. Attackers may run brute-forcing attacks on the content of the guest authentication token and discover user credentials. For a practical attack vector, the guest users needs to have logged in, the content of the guest user's "OxReaderID" cookie and the value of the "auth" parameter needs to be known to the attacker.

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Glexia's TakeAutomated analysis

Security readout for executives and security teams

CVE-2016-4028 affects Open-Xchange OX Guard before 2.4.0-rev8. A flaw in how guest authentication tokens are checked can leak enough information for an attacker to brute-force token contents and potentially recover guest user credentials. Exposure is limited to organizations running Open-Xchange OX Guard versions before 2.4.0-rev8 and using guest-user access flows. The practical attack requires attacker knowledge of the guest user’s OxReaderID cookie and auth parameter. Prioritize remediation where OX Guard guest access is internet-facing or used for sensitive communications. The issue can expose credentials, but exploitation requires specific token material, reducing broad urgency. Mitigation focus: Upgrade OX Guard to 2.4.0-rev8 or later if running an affected version.; Review the Open-Xchange advisory for the supported remediation path.; Identify and retire unsupported OX Guard deployments..

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