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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2021.3023 Another race in XENMAPSPACE_grant_table handling 9 September 2021 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: Xen Publisher: Xen Operating System: Xen Virtualisation Impact/Access: Increased Privileges -- Existing Account Denial of Service -- Existing Account Access Confidential Data -- Existing Account Resolution: Patch/Upgrade CVE Names: CVE-2021-28701 Original Bulletin: http://xenbits.xen.org/xsa/advisory-384.html - --------------------------BEGIN INCLUDED TEXT-------------------- - -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory CVE-2021-28701 / XSA-384 version 3 Another race in XENMAPSPACE_grant_table handling UPDATES IN VERSION 3 ==================== Public release. ISSUE DESCRIPTION ================= Guests are permitted access to certain Xen-owned pages of memory. The majority of such pages remain allocated / associated with a guest for its entire lifetime. Grant table v2 status pages, however, are de-allocated when a guest switches (back) from v2 to v1. Freeing such pages requires that the hypervisor enforce that no parallel request can result in the addition of a mapping of such a page to a guest. That enforcement was missing, allowing guests to retain access to pages that were freed and perhaps re-used for other purposes. Unfortunately, when XSA-379 was being prepared, this similar issue was not noticed. IMPACT ====== A malicious guest may be able to elevate its privileges to that of the host, cause host or guest Denial of Service (DoS), or cause information leaks. VULNERABLE SYSTEMS ================== All Xen versions from 4.0 onwards are affected. Xen versions 3.4 and older are not affected. Only x86 HVM and PVH guests permitted to use grant table version 2 interfaces can leverage this vulnerability. x86 PV guests cannot leverage this vulnerability. On Arm, grant table v2 use is explicitly unsupported. MITIGATION ========== Running only PV guests will avoid this vulnerability. Suppressing use of grant table v2 interfaces for HVM or PVH guests will also avoid this vulnerability. NOTE REGARDING EMBARGO ====================== Please note that the public embargo time for this advisory is 2021-09-08, two weeks later than XSA-378,379,380,382,383. CREDITS ======= This issue was discovered by Julien Grall of Amazon. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. 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. xsa384.patch xen-unstable - Xen 4.15.x xsa384-4.14.patch Xen 4.14.x - 4.12.x xsa384-4.11.patch Xen 4.11.x $ sha256sum xsa384* 3bf555e8b2a37dec361b86c0b6a3f59af2e1a24e3457ed92e0cfeaa662f1663a xsa384.patch 435b431dc77d255031832dc265a8d5aa2f13f3b1a7de497b62ac2df5ad61da90 xsa384-4.11.patch f98ec4c25fb122de6353eb7d9f5678dd09982f887bf201d6f178e9b647618c9a xsa384-4.14.patch $ DEPLOYMENT DURING EMBARGO ========================= Deployment of the patches and/or PV-guest-only mitigations 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, distribution of updated software is prohibited (except to other members of the predisclosure list). ADDITIONALLY, deployment of the grant table v2 disabling mitigation described above *is* now (following the public release of XSA-379) permitted during the embargo on public-facing systems with untrusted guest users and administrators. This is because (although such a configuration change is recognizable by the affected guests) it is a mitigation recommended in XSA-379, so such a change would not reveal the existence of a further problem. 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----- iQE/BAEBCAAqFiEEI+MiLBRfRHX6gGCng/4UyVfoK9kFAmE4rD4MHHBncEB4ZW4u b3JnAAoJEIP+FMlX6CvZ8S8H+ITq1u5AaK+N1wgsgztLJRh1cjFTDaLZdI0mypwV +wPhNdw1FFH19wYDZhOJIzv3h5352YVUYs8P6HvhFWrsUaq5n4cz17wxUHch74r3 MUUU9WUdTffQrAAOSSK65yWTUewv/FglEWP55YFBDPqBJHpVWt2MMidmP6My6azK GZAHSWU7+qNXbs4/OM+dQJyUJm6yZtAltVtVmiJdJ5bSZyqe+82zRMnS39jlkZEh VwFnw6rdlPcYO/fNYi25bQSlXbFeruSJYK+omrrFsyd65Z4D5LyZc5CQkfRJgEt6 vMDsQR+5hrE/KXKr2mfyTx6nh0RdR8kcI2Wh017BYuLqhA== =AEo5 - -----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 iQIVAwUBYTlEvuNLKJtyKPYoAQjnJQ/+M9f6nDEFgSpFnscMWyAmL5MCIN46+dA1 c+CSJi3oNMA5Ffs1kbDXCfQTrLfjolIZ7neBVncoRWN3gPi/dPZLtnPJhQa1eofy mQXtWgbu2f2eC9rYrksuFa5fnRcNF/ZLNIPS4u55rh6ey9lgfkMGRFyPoq4Mqf0Q 82U1CMHavLgAUu3jhEp+Yb5Qs2Q2hIZc3PgbtdYd20j5e8mxblPw0oxKz+Xaxnqq dgQAyL6gxj/DqZ82CH1ovqchokPjtcqHFDuuNhbJv7TMd34QG/CVijUuOEM0Nk21 xheVgiWAos/Ccahpr40hDTbPnqfL8mZXSOF4Gs1ESh/AV8m9TpCtqLovlbDrjETa JscNWfVhmmbg1+9X0NoJM50HOL/rtuqIoYmDOQs+xxYfu4fxFI//Bly09C6tnG2j PyiTZPfqxmsI7wQlrT7QOIUIN615VRxwwyUwrR8cmPoyltlx3Qt514rEsUxwZLx3 /Cacdtu/IzijTNl7+wOTqWjwjE1+YNqVB4jTal6prayvezcXUyD9mxTw+0X5MDiI HNAbBolqyt1SsUxcm8zYtlh2q6zMAbB35aVMk83+qO1dQfoy3bIoa2AHP7meyfc8 H3o/dIrQ5IXhwS6kU/RLtMyUUrgJotsYKOkdF+Oqtg+AQNAvZMURY8Klgl2TRg6s 55z6QwqJK0E= =Wp0f -----END PGP SIGNATURE-----