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Category:   Device (Encryption/VPN)  >   Citrix NetScaler Vendors:   Citrix
Citrix NetScaler TLS Side Channel Leakage Flaw Lets Remote Users Decrypt TLS Session Data
SecurityTracker Alert ID:  1039985
SecurityTracker URL:
CVE Reference:   CVE-2017-17382   (Links to External Site)
Date:  Dec 12 2017
Impact:   Disclosure of system information, Disclosure of user information
Fix Available:  Yes  Vendor Confirmed:  Yes  Exploit Included:  Yes  
Version(s): 10.5, 10.5, 11.0, 11.0, 11.1, 11.1, 12.0, 12.0
Description:   A vulnerability was reported in Citrix NetScaler. A remote user can decrypt data in certain cases.

A remote user that can monitor TLS session data between the target client and target server and with the ability to establish a large number of TLS connections with the target server can conduct a modified version of the Bleichenbacher chosen-ciphertext attack against RSA PKCS#1 v1.5 encryption block formatting to decrypt the data.

Systems that are configured to only use Perfect Forward Secrecy (PFS) cipher suites are not affected.

This attack method is known as the "ROBOT" attack.

The origin advisory ("Return Of Bleichenbacher's Oracle Threat") is available at:

Hanno Bock, Juraj Somorovsky of Ruhr-Universitat Bochum/Hackmanit GmbH, and Craig Young of Tripwire VERT reported this vulnerability.

Impact:   A remote user can decrypt TLS session data in certain cases.
Solution:   Citrix has issued a fix (10.5 build 67.13, 11.0 build 71.22, 11.1 build 56.19, 12.0 build 53.22).

[Editor's note: The vendor notes that if TLS private keys are shared between multiple devices, all devices must be patched, as a single device can be used to decrypt TLS traffic handled by the other device(s) when TLS private keys are shared.]

The vendor advisory is available at:

Vendor URL: (Links to External Site)
Cause:   Access control error, State error

Message History:   None.

 Source Message Contents

[Original Message Not Available for Viewing]

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