Date: Tue, 15 Dec 2020 12:20:17 +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 323 v3 (CVE-2020-29482) - Xenstore: wrong path length check -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 Xen Security Advisory CVE-2020-29482 / XSA-323 version 3 Xenstore: wrong path length check UPDATES IN VERSION 3 ==================== Public release. ISSUE DESCRIPTION ================= A guest may access xenstore paths via absolute paths containing a full pathname, or via a relative path, which implicitly includes /local/domain/$DOMID for their own domain id. Management tools must access paths in guests' namespaces, necessarily using absolute paths. oxenstored imposes a path name limit which is applied solely to the relative or absolute path specified by the client. Therefore, a guest can create paths in its own namespace which are too long for management tools to access. IMPACT ====== Depending on the toolstack in use, a malicious guest administrator might cause some management tools and debugging operations to fail. For example, a guest administrator can cause `xenstore-ls -r` to fail. However a guest administrator cannot prevent the host administrator from tearing down the domain. VULNERABLE SYSTEMS ================== All systems using oxenstored are vulnerable. Building and using oxenstored is the default in the upstream Xen distribution, if the Ocaml compiler is available. Systems using C xenstored are not vulnerable. MITIGATION ========== There are no mitigations. Changing to use of C xenstored would avoid this vulnerability. However, given the other vulnerabilities in both versions of xenstored being reported at this time, changing xenstored implementation is not a recommended approach to mitigation of individual issues. CREDITS ======= This issue was discovered by Edwin Török and analysed by Andrew Cooper, both of Citrix. 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. xsa323.patch xen-unstable - Xen 4.11.x xsa323-4.10.patch Xen 4.10.x $ sha256sum xsa323* b693f259d92033ffc568412f1ea591b63d7e8dcaa7f88b62158b3c09e65ad122 xsa323.meta fdfefa3c064c6c5f49d666d7c3444f919777d557c8cb9c2e9ae6ac94711d37de xsa323.patch 90ab525fad3f43b6de2858f8a58128ce0d4ca97f5960bcd2af5be55d49059c92 xsa323-4.10.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+FMlX6CvZNeEH/iXf3oBcCJAICRa2WuXXR8zs/R/GUaiQCJYvU2So OBil7cnb6bIomVmDd7TxjYUaHL3ilMEFHPTbUq0gLLKPlaJqVJTLyxDzss6VEmqp eyQ8GBRODHLHCGcQaS3eKtCN9e6Oyd+rEm5CIPXvcu+g+HVnxG1BCdzHOei7NEPS P5rmOn3Gkv6LlYQpVPYzVX3baIpLe09Ha+1iCS2bflArPgAc23ajxHHffuI90TIF cBjN93AOpgBc89wGM0G11NSPAjnVUWe69qLJp6HDW6mQRaUxHQVbpBesd0V43/9P XCvo6TxWdfDgJFOubZRKg6jHP5CKqobL4PZZT+X1MC8ZNbI= =ilKH -----END PGP SIGNATURE----- Download attachment "xsa323.meta" of type "application/octet-stream" (1913 bytes) Download attachment "xsa323.patch" of type "application/octet-stream" (5747 bytes) Download attachment "xsa323-4.10.patch" of type "application/octet-stream" (5216 bytes)
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