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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2021.2044 Guest triggered use-after-free in Linux xen-netback 9 June 2021 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: Linux kernel Publisher: Xen Operating System: Xen Linux variants Impact/Access: Increased Privileges -- Existing Account Denial of Service -- Existing Account Access Confidential Data -- Existing Account Resolution: Patch/Upgrade CVE Names: CVE-2021-28691 Original Bulletin: http://xenbits.xen.org/xsa/advisory-374.html Comment: This advisory references vulnerabilities in products which run on platforms other than Xen. It is recommended that administrators running Linux kernel check for an updated version of the software for their operating system. - --------------------------BEGIN INCLUDED TEXT-------------------- - -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory CVE-2021-28691 / XSA-374 version 2 Guest triggered use-after-free in Linux xen-netback UPDATES IN VERSION 2 ==================== Public release. ISSUE DESCRIPTION ================= A malicious or buggy network PV frontend can force Linux netback to disable the interface and terminate the receive kernel thread associated with queue 0 in response to the frontend sending a malformed packet. Such kernel thread termination will lead to a use-after-free in Linux netback when the backend is destroyed, as the kernel thread associated with queue 0 will have already exited and thus the call to kthread_stop will be performed against a stale pointer. IMPACT ====== A malicious or buggy frontend driver can trigger a dom0 crash. Privilege escalation and information leaks cannot be ruled out. VULNERABLE SYSTEMS ================== Systems using Linux version 5.5 or newer are vulnerable. MITIGATION ========== On x86 running only HVM guests with emulated network cards will avoid the issue. There's however no option in the upstream toolstack to offer only emulated network cards to guests. CREDITS ======= This issue was discovered by Michael Brown of iPXE and diagnosed by Olivier Benjamin, Michael Kurth and Martin Mazein of AWS. RESOLUTION ========== Applying the attached patch resolves this issue. xsa374-linux.patch Linux 5.5.0 - 5.12.2 $ sha256sum xsa374* 156cee65022359a5901cce97714d2abb16fef786246b1c4bf509083d21e085d6 xsa374-linux.patch $ DEPLOYMENT DURING EMBARGO ========================= Deployment of the patches and/or 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. But: Distribution of updated software is prohibited (except to other members of the predisclosure list). Deployment of the mitigation to disable PV network interfaces is NOT permitted (except where all the affected systems and VMs are administered and used only by organisations which are members of the Xen Project Security Issues Predisclosure List). Specifically, deployment on public cloud systems is NOT permitted. 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/4UyVfoK9kFAmC/oxIMHHBncEB4ZW4u b3JnAAoJEIP+FMlX6CvZigoIAKNYimzTYl6VQYaqgwMdNzqXCF/PdlQF/tf8PSwm 5VP0ZPbLq6Zn4HOgMBtBzs/GCFtrIWsQGnZji611dkaAh21N1YErXW5jFYMnf1DI rruCXE1GuL5B4sFvWw7CnMXax6vYe0q5KPoGmyZRV77aT5T+gNMONlGl6raw7/Ne UAtAv4JDSR5Nc53X0HNK7tNU9tdr4VaLqEKWs+C0W+azOFNGvrTeNDVjBiLqDZbA st62i3PIFTXu+XzbjZNdM/RMpVVxFSkfdWn53RDVJ2JaFBMxrcVs75aVo3Nfr34Z Iho+eTPDywP9+4zl/FoModMYHg4rTMHf+jmbi3M/aCOal2U= =1Dhy - -----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 iQIVAwUBYMBdD+NLKJtyKPYoAQjVxxAAsUxlto3i1sWkysCWGgR2sqF8L5kSZ8S+ eYHW9ZLnaIzW7VLUp3XpBh0FQloUDgihS/2FFjgFiX8ZDugRzRvJRcmMqGATimXk Pv6i1uwtShLGiKRIvyaxOy2ONlMvuD7yM4r1qfYdEgPBCuqK0Z9qA78BJR4qBooQ Tipy6MC/DtV5BYZxo3qYsbTA+mYvgHpOkmnI/q0l3MjhC02Rp+CMjpjf4dgYPLqJ 0MH5XUo12pF1wxhbJRsPgiJNLsANhkyKCZHdXQpEddsVvQmHaztuGdbL1FanAyPE BfgzS/trJ22l2d0HzBCsmCNUbxlbqlaNgMeq0J5+RnbDFRMBzDFIIlB2k9p9txGc oApc8LzWGoiFt3vT7AxY74tp/W1qLUzk/R1oticUxK53Xhrl1mUyEQPS2ARHtA7X 0G768GPX/QxIoY59m0mghzoSYThfg3mMzRVPYx8R2G+Hr+Vu79Y2x6U/z+fxRq5M FVIvppJX5mvoTjOacHSmu3IsRN8pJHuPSqJpQN6K+/M93vH/WTQDLIXbhTd2CQxa vBwsRv9pUlnU0laKnfdJ+9qNXaxteTCX8ts58ZxuexS8ws8W5mHujk3h6Fl4BAbc WOOIrd+P/rUq4njRki31tCGhEZYs5Mo0DhR/pKQcc27IEssZNFhwaZHCruAl9I+g WbagREpqmU0= =Lnv1 -----END PGP SIGNATURE-----