Protect yourself against future threats.
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2021.3980 Denial of Service vulnerability found in Xen 24 November 2021 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: Xen Publisher: Xen Operating System: Virtualisation Impact/Access: Denial of Service -- Existing Account Resolution: Patch/Upgrade CVE Names: CVE-2021-28706 Original Bulletin: http://xenbits.xen.org/xsa/advisory-385.html - --------------------------BEGIN INCLUDED TEXT-------------------- - -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory CVE-2021-28706 / XSA-385 version 2 guests may exceed their designated memory limit UPDATES IN VERSION 2 ==================== Add CVE numbers to patches. Public release. ISSUE DESCRIPTION ================= When a guest is permitted to have close to 16TiB of memory, it may be able to issue hypercalls to increase its memory allocation beyond the administrator established limit. This is a result of a calculation done with 32-bit precision, which may overflow. It would then only be the overflowed (and hence small) number which gets compared against the established upper bound. IMPACT ====== A guest may be able too allocate unbounded amounts of memory to itself. This may result in a Denial of Service (DoS) affecting the entire host. VULNERABLE SYSTEMS ================== All Xen versions from at least 3.2 onwards are affected. On x86, only Xen builds with the BIGMEM configuration option enabled are affected. (This option is off by default.) Only hosts with more than 16 TiB of memory are affected. MITIGATION ========== Setting the maximum amount of memory a guest may allocate to strictly less than 1023 GiB will avoid the vulnerability. CREDITS ======= This issue was discovered by Julien Grall of Amazon. RESOLUTION ========== Applying the appropriate first attached patch resolves this specific issue. The second patch in addition documents altered support status of Xen on huge memory systems. Note that patches for released versions are generally prepared to apply to the stable branches, and may not apply cleanly to the most recent release tarball. Downstreams are encouraged to update to the tip of the stable branch before applying these patches. xsa385-.patch xen-unstable xsa385-4.15.patch Xen 4.15.x - 4.14.x xsa385-4.13.patch Xen 4.13.x xsa385-4.12.patch Xen 4.12.x $ sha256sum xsa385* b278902e293730a117605200910180bb842cf95db4bdedfd54b42b7314041d8c xsa385-1.patch 46a5ccfbb763b857f6cd0df46a9b7eed155b9de399ca4c68c9925faf4d1d9adb xsa385-2.patch 69ebe63dc7dca71f74260af19205a6387be56c7dc67b97fa7695ab1acd3c4da4 xsa385-4.12.patch 858eaad715e7cc62c4ab9784360f4ec77df70b2636b0755afe780d5c618cf9b4 xsa385-4.13.patch 831e86c3adfec532b1a48a0b967b7c58c37db3733aee8d78216eb9d535b34f12 xsa385-4.15.patch $ DEPLOYMENT DURING EMBARGO ========================= Deployment of the patches described above (or others which are substantially similar) is permitted during the embargo, even on public- facing systems with untrusted guest users and administrators. HOWEVER, deployment of the mitigation described above is NOT permitted during the embargo on public-facing systems with untrusted guest users and administrators. This is because such a configuration change is recognizable by the affected guests. AND: Distribution of updated software is prohibited (except to other members of the predisclosure list). Predisclosure list members who wish to deploy significantly different patches and/or mitigations, please contact the Xen Project Security Team. (Note: this during-embargo deployment notice is retained in post-embargo publicly released Xen Project advisories, even though it is then no longer applicable. This is to enable the community to have oversight of the Xen Project Security Team's decisionmaking.) For more information about permissible uses of embargoed information, consult the Xen Project community's agreed Security Policy: http://www.xenproject.org/security-policy.html - -----BEGIN PGP SIGNATURE----- iQFABAEBCAAqFiEEI+MiLBRfRHX6gGCng/4UyVfoK9kFAmGc2jYMHHBncEB4ZW4u b3JnAAoJEIP+FMlX6CvZEd4IAMwrHHAqFvSHgZ8Uw+DzMeT54db9nowudP9i/kYy +KobbVlGkxwLAU3mvh5lRkOLYzoIonrcA99cajZQNIcOKt3Mfi/8qzGGUN+hWZvh 6EZo3m7+7vx9mhtAeDBUbjkcZBLiVyxRAWALMS67ScBEX9lZTvbyj9nGkdQJmmfR pKt98z2Da2uR9YF521KWobuPYC0AFXujYBoavaTQpU/M8SiM+Wp1A2Fc6ZG+9ZKo frMeqFbHvwj94Hbqpn6CoLu2d/XnykMvttuLlqCKTccQc3puHXdQRz14W8IxxGYx gqYaIShZCFw/bUCu8mYHroDUlELJI3PIWQ1nJxy02bd5+N0= =7E6A - -----END PGP SIGNATURE----- - --------------------------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. The decision to follow or act on information or advice contained in this security bulletin is the responsibility of each user or organisation, and should be considered in accordance with your organisation's site policies and procedures. AusCERT takes no responsibility for consequences which may arise from following or acting on information or advice contained in this security bulletin. NOTE: This is only the original release of the security bulletin. It may not be updated when updates to the original are made. If downloading at a later date, it is recommended that the bulletin is retrieved directly from the author's website to ensure that the information is still current. Contact information for the authors of the original document is included in the Security Bulletin above. If you have any questions or need further information, please contact them directly. 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). On call after hours for member emergencies only. =========================================================================== -----BEGIN PGP SIGNATURE----- Comment: http://www.auscert.org.au/render.html?it=1967 iQIVAwUBYZ2ZH+NLKJtyKPYoAQiRxBAAsiZnafCmJgwuG0xgaE5CCeh6tg6hggmd aPmdFXEzBb4yhVtKMhh8Hr1jVeSqYgT1UTQ3qzQfpWIaEdgejymU9tKubL1zFIp6 snf3XwxG9SHpeiBhNTp2UMMmMx0p4UhuGDQ/PeBJKy031DGME/H9vlqU6DXoOT8k 561RRig3mqKQKRze7hScKoa2p9TimliMbt9Eewh2tqGdYpdnOAWgwtmSNXaqjO7K k4nv5hncmpKo0fBZadhYN0fFt92r9z+c4VyAgqwE1pj1aAW++PTM8VAooliND/se 3KKG/NPqqsk8pEcrYGKEd/istbGDVWM3hrOhEIkD31w1DhhaJ3Z9W/vUphiGrOXO uts5gIoab2eI/cN0ED8AMDvr9YeWMoiMVBbjbhSMGPEKHoBSyuDHVl4BBd45NceL Vfmt8fVKOMU8PURHhQbEmPFBC8aRDAxBNP19WTWmuLtqjXJ1XIqggpPsMcI0VpzM HPjvUf1++w/0HpjDyYBqf+UvhTxM11HYHuWrPVUHOTLsPjJB9QqG8dGs+zIlphbj Met8oYJebAxh2hCOUJvVzKDVrxmBVHa/cYQ59uPV2RewKLJSbIgxAP1UAbHLoUyt mjvOQWOt5WpRkbZTTu3HkeIMOSyABG58hMXMmYM+Sri6/sFGhUppSFNGwNN+BPcF lQ9YpgNwIzU= =XdHS -----END PGP SIGNATURE-----