Date: Tue, 08 Jun 2021 17:04:30 +0000 From: Xen.org security team <security@....org> To: xen-announce@...ts.xen.org, xen-devel@...ts.xen.org, xen-users@...ts.xen.org, oss-security@...ts.openwall.com CC: Xen.org security team <security-team-members@....org> Subject: Xen Security Advisory 374 v2 (CVE-2021-28691) - Guest triggered use-after-free in Linux xen-netback -----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----- Download attachment "xsa374-linux.patch" of type "application/octet-stream" (1678 bytes)
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