Date: Tue, 15 Dec 2020 12:20:16 +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 322 v4 (CVE-2020-29481) - Xenstore: new domains inheriting existing node permissions -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory CVE-2020-29481 / XSA-322 version 4 Xenstore: new domains inheriting existing node permissions UPDATES IN VERSION 4 ==================== Public release. ISSUE DESCRIPTION ================= Access rights of Xenstore nodes are per domid. Unfortunately, existing granted access rights are not removed when a domain is destroyed. This means that a new domain created with the same domid will inherit the access rights to Xenstore nodes from the previous domain(s) with the same domid. All Xenstore entries of a guest below /local/domain/<domid> are deleted by Xen tools when a guest is destroyed. Therefore only entries belonging to other guests, referring to the deleted guests, are potentially affected. IMPACT ====== In some circumstances, it might be possible for a new guest domain to access resources belonging to a previous domain. The impact would depend on the software in use and the configuration, but might include any of denial of service, information leak, or privilege escalation. VULNERABLE SYSTEMS ================== All versions of Xen are in principle vulnerable. Both Xenstore implementations (C and Ocaml) are vulnerable. Vulnerable systems are only those running software where one domain is granted access to another's xenstore nodes, without complete cleanup of those nodes on domain destruction. No such software is enabled in default configurations of upstream Xen. Therefore upstream Xen, without additional management software (in host or guest(s)), is not vulnerable in the default (host and guest) configuration. MITIGATION ========== There is no mitigation available. CREDITS ======= This issue was discovered by Jürgen Groß of SUSE. 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. xsa322-c.patch xen-unstable [C xenstored] xsa322-4.14-c.patch Xen 4.14 - 4.13 [C xenstored] xsa322-4.13-c.patch Xen 4.12 - 4.10 [C xenstored] xsa322-o.patch xen-unstable - 4.12 [Ocaml xenstored] xsa322-4.11-o.patch Xen 4.11 - 4.10 [Ocaml xenstored] $ sha256sum xsa322* 89e40422e41b8b2f8926ee5081da0e494e8e7312091151d31bfaa29eefa9b669 xsa322.meta 0cfeb0f8dd1c95e628e06f3402cbb5fb58c0972d6616958f5a0fbed59813dd6c xsa322-4.11-o.patch d4f9362b6f7ebfb7349849d4449f70b6004779c35238dc628736c541fe9e4279 xsa322-4.12-c.patch 8efe8fc39bf91a1c0cbdbf572deb2592930b757725951f4fdf0c387904ce4293 xsa322-4.14-c.patch 9275c7c36127f0e9719d4cb3162e39ce9233b2b55e9f9307b4c4d370a7b636a3 xsa322-c.patch 42c0818ceff11792517530237c4972967099c9828b4e2b5ec4bf6bfc1825cd7c xsa322-o.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). 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/4UyVfoK9kFAl/Yqd4MHHBncEB4ZW4u b3JnAAoJEIP+FMlX6CvZm4QH/A4suMmviY3ihK5d97oiKhJWg/5bgt6ePoJtZwAe 28nqNX3pI3+hi09RTAUpINVXt+3ealblDs9XY4u+2trTX7yqtbdtRrMF+mhkHueK Pnqvp3qSREDNaAJUN5gmsJ9vfgNwYTWscHqYga69cq4bHaLZJnEZC1He2qvvac67 MmKJk69go6VxCLG6ZAU59aHXzfs0EoQGKPhV6+Fw41HK9CNG8YErfdK1h2RIJ6Jg GIf0bhgNSPxMs/0wcKJDmj4u3kmFStfDJbzsYxjmu5K0MZVMD87cQv89EHC+gCCc e4ipgRwM6ba7pD338JT42gDHptqj2Rhg1YszmG2bQO0TQoA= =MQnE -----END PGP SIGNATURE----- Download attachment "xsa322.meta" of type "application/octet-stream" (2033 bytes) Download attachment "xsa322-4.11-o.patch" of type "application/octet-stream" (4524 bytes) Download attachment "xsa322-4.12-c.patch" of type "application/octet-stream" (16469 bytes) Download attachment "xsa322-4.14-c.patch" of type "application/octet-stream" (16424 bytes) Download attachment "xsa322-c.patch" of type "application/octet-stream" (16388 bytes) Download attachment "xsa322-o.patch" of type "application/octet-stream" (4523 bytes)
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