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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2018.0065 Citrix XenServer Multiple Security Updates 5 January 2018 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: Citrix XenServer Publisher: Citrix Operating System: Xen Impact/Access: Access Privileged Data -- Existing Account Denial of Service -- Existing Account Resolution: Patch/Upgrade CVE Names: CVE-2017-5754 CVE-2017-5753 CVE-2017-5715 Reference: ASB-2018.0002.3 ESB-2018.0060 ESB-2018.0059 ESB-2018.0057 ESB-2018.0044 ESB-2018.0042 Original Bulletin: https://support.citrix.com/article/CTX231390 - --------------------------BEGIN INCLUDED TEXT-------------------- CTX231390 Citrix XenServer Multiple Security Updates Security Bulletin | High | Created: 04 Jan 2018 | Modified: 04 Jan 2018 Applicable Products XenServer 7.3 XenServer 7.2 XenServer 7.1 LTSR Cumulative Update 1 XenServer 7.0 XenServer 6.5 XenServer 6.2.0 XenServer 6.0.2 Description of Problem This hotfix provides mitigations for certain recently disclosed vulnerabilities in the speculative execution functionality of multiple vendors' CPUs: CVE-2017-5753, also known as ‘Variant 1: bounds check bypass’ CVE-2017-5715, also known as ‘Variant 2: branch target injection’ CVE-2017-5754, also known as ‘Variant 3: rogue data cache load’ For Variant 1, Citrix is not currently aware of any exploit vectors in Citrix XenServer. For Variant 2, an attacker running code in a guest VM may be able to read in-memory data from other VMs on the same host. This is independent of the CPU vendor. For Variant 3, an attacker running code in a 64 bit PV guest VM running on an Intel CPU may be able to read in-memory data from other VMs on the same host. As these are issues in the underlying hardware, all versions of Citrix XenServer are affected. In addition to the mitigations for these CPU speculative execution issues, this hotfix also addresses a number of vulnerabilities that have been identified in Citrix XenServer: CVE-2017-TBD - x86 PV guests may gain access to internally used pages CVE-2017-TBD - broken x86 shadow mode refcount overflow check CVE-2017-TBD - improper x86 shadow mode refcount error handling CVE-2017-TBD - improper bug check in x86 log-dirty handling Collectively, these four issues could allow a malicious guest administrator to crash the host. What Customers Should Do The CPU speculative execution mitigations require system firmware/BIOS upgrades to be applied before becoming fully effective. Citrix strongly recommends that customers contact their hardware vendors for further information on these firmware upgrades. As these issues are in optimisation features of the underlying physical CPU, mitigating them will necessarily cause a reduction of CPU performance. This performance impact will depend on a number of factors, including workload and CPU model. Customers are recommended to monitor their system loads after installing these hotfixes. After applying the relevant firmware/BIOS upgrades and XenServer hotfixes, guest VMs will need to be fully shut down and started at least once after the application of relevant guest operating system updates. This will allow any corresponding security updates for the guest operating system to become fully effective. Citrix has released hotfixes that contain mitigations for Variant 2. These hotfixes can be found on the Citrix website at the following locations: Citrix XenServer 7.3: Citrix is actively working on a hotfix for this version. This document will be updated when a hotfix is available. Citrix XenServer 7.2: Citrix is actively working on a hotfix for this version. This document will be updated when a hotfix is available. Citrix XenServer 7.1 LTSR CU1: CTX230788 – https://support.citrix.com/article/ctx230788 Citrix XenServer 7.0: Citrix is actively working on a hotfix for this version. This document will be updated when a hotfix is available. Note that these updates are not Livepatchable. Customers using End of Maintenance versions of Citrix XenServer, i.e. Citrix XenServer version 6.0.2 Common Criteria, 6.2 SP1 and 6.5 SP1 are strongly recommended to upgrade to a more recent version. Citrix is actively working on additional mitigations for Variant 3, but strongly recommends that customers that have deployed untrusted PV guests on Intel CPUs consider transitioning to HVM-based guests. What Citrix Is Doing Citrix is notifying customers and channel partners about this potential security issue. This article is also available from the Citrix Knowledge Center at http://support.citrix.com/. Obtaining Support on This Issue If you require technical assistance with this issue, please contact Citrix Technical Support. Contact details for Citrix Technical Support are available at https://www.citrix.com/support/open-a-support-case.html. Reporting Security Vulnerabilities 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 – Reporting Security Issues to Citrix Changelog Date Change 4th January 2018 Initial publishing - --------------------------END INCLUDED TEXT-------------------- You have received this e-mail bulletin as a result of your organisation's registration with AusCERT. The mailing list you are subscribed to is maintained within your organisation, so if you do not wish to continue receiving these bulletins you should contact your local IT manager. If you do not know who that is, please send an email to auscert@auscert.org.au and we will forward your request to the appropriate person. NOTE: Third Party Rights This security bulletin is provided as a service to AusCERT's members. As AusCERT did not write the document quoted above, AusCERT has had no control over its content. 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Previous advisories and external security bulletins can be retrieved from: https://www.auscert.org.au/bulletins/ =========================================================================== Australian Computer Emergency Response Team The University of Queensland Brisbane Qld 4072 Internet Email: auscert@auscert.org.au Facsimile: (07) 3365 7031 Telephone: (07) 3365 4417 (International: +61 7 3365 4417) AusCERT personnel answer during Queensland business hours which are GMT+10:00 (AEST). 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