CVE-2018-18883 - Citrix XenServer Security Update

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<h2> Description of Problem</h2>

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<p>A security issue has been identified in Citrix XenServer that may allow a malicious administrator of an HVM guest VM to crash the host.</p>
<p>This issue affects the following versions of Citrix XenServer: </p>
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<li>Citrix XenServer 7.6</li>
<li>Citrix XenServer 7.5</li>
<li>Citrix XenServer 7.1 LTSR CU1 </li>
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<p>The following vulnerabilities have been addressed: </p>
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<li>CVE-2018-18883: Nested VT-x usable even when disabled</li>
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<h2> Mitigating Factors</h2>

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<p>Customers with only PV guests are not affected by this issue.</p>
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<h2> What Customers Should Do</h2>

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<p>Hotfixes have been released to address this issue. Citrix recommends that affected customers install these hotfixes as their patching schedule permits. The hotfixes can be downloaded from the following locations:</p>
<p> <br /> Citrix XenServer 7.6: CTX239128 – <a href=“https://support.citrix.com/article/CTX239128”>https://support.citrix.com/article/CTX239128</a><br /> Citrix XenServer 7.5: CTX239127 – <a href=“https://support.citrix.com/article/CTX239127”>https://support.citrix.com/article/CTX239127</a><br /> Citrix XenServer 7.1 LTSR CU1: CTX239126 – <a href=“https://support.citrix.com/article/CTX239126”>https://support.citrix.com/article/CTX239126 </a></p>
<p>Customers who are using the LivePatching feature of Citrix XenServer will not need to reboot servers to apply this hotfix if those servers were previously fully patched.<br /> </p>
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<h2> What Citrix Is Doing</h2>

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<p>Citrix is notifying customers and channel partners about this potential security issue. This article is also available from the Citrix Knowledge Center at <u> <a href=“http://support.citrix.com/”>http://support.citrix.com/</a></u>.</p>
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<h2> Obtaining Support on This Issue</h2>

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<p>If you require technical assistance with this issue, please contact Citrix Technical Support. Contact details for Citrix Technical Support are available at <u> <a href=“https://www.citrix.com/support/open-a-support-case.html”>https://www.citrix.com/support/open-a-support-case.html</a></u>. </p>
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<h2> Reporting Security Vulnerabilities</h2>

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<p>Citrix welcomes input regarding the security of its products and considers any and all potential vulnerabilities seriously. For guidance on how to report security-related issues to Citrix, please see the following document: CTX081743 – <a href=“http://support.citrix.com/article/CTX081743”>Reporting Security Issues to Citrix</a></p>
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<h2> Changelog</h2>

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<table border=“1” width=“100%”>
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<td>Date </td>
<td>Change</td>
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<td width=“50%”>26th October 2018 </td>
<td>Initial Issue </td>
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<td valign=“top”>1st November 2018</td>
<td>Update with assigned CVE number </td>
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