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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2013.1552 Xen Security Advisory CVE-2013-4416 / XSA-72 version 3 31 October 2013 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: Xen Publisher: Xen Operating System: UNIX variants (UNIX, Linux, OSX) Impact/Access: Denial of Service -- Remote/Unauthenticated Resolution: Patch/Upgrade CVE Names: CVE-2013-4416 Original Bulletin: http://xenbits.xen.org/xsa/advisory-72.html - --------------------------BEGIN INCLUDED TEXT-------------------- - -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Xen Security Advisory CVE-2013-4416 / XSA-72 version 3 ocaml xenstored mishandles oversized message replies UPDATES IN VERSION 3 ==================== Public release. ISSUE DESCRIPTION ================= The Ocaml xenstored implementation ("oxenstored") cannot correctly handle a message reply larger than XENSTORE_PAYLOAD_SIZE when communicating with a client domain via the shared ring mechanism. When this situation occurs the connection to the client domain will be shutdown and cannot be restarted leading to a denial of service to that domain. Clients in the same domain as xenstored which are using the Unix domain socket mechanism are not vulnerable. IMPACT ====== A malicious domain can create a directory containing a large number of entries in the hopes that a victim domain will attempt to list the contents of that directory. If this happens then the victim domain's xenstore connection will be shutdown leading to a denial of service against that domain. If the victim domain is a toolstack or control domain then this can lead to a denial of service against the whole system. VULNERABLE SYSTEMS ================== All systems using oxenstored are potentially vulnerable. oxenstored was added in Xen 4.1.0. From Xen 4.2.0 onward it is used by default if an ocaml toolstack was present at build time. In its default configuration the C xenstored implementation is not vulnerable. By default this implementation imposes a quota on the maximum directory size which is less than XENSTORE_PAYLOAD_SIZE. If you have adjusted the quota using the --entry-size / -S option to a value larger than XENSTORE_PAYLOAD_SIZE (4096 bytes) then you may be vulnerable. Systems where the toolstack and oxenstored live in the same domain will default to using Unix domain socket based communications and therefore are not vulnerable to the host wide denial of service by default. In such a configuration guest domains which do not list xenstore paths belonging to untrusted foreign domains will not be vulnerable to the DoS. (In the common case guests will not have permission to do so in any case.) MITIGATION ========== Switching to the C xenstored (in its default configuration), will eliminate this vulnerability. CREDITS ======= This issue was discovered by Thomas Sanders at Citrix. RESOLUTION ========== Applying the appropriate attached patch resolves both the ocaml xenstore and C xenstore issues. xsa72.patch xen-unstable, Xen 4.3.x, Xen 4.2.x $ sha256sum xsa72*.patch 66e11513fc512173140f3ca12568f8ef79415e9a7884254a700991b3f1afd125 xsa72.patch $ - -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iQEcBAEBAgAGBQJSb9aMAAoJEIP+FMlX6CvZU6MH/2Racg6r+JLka2jqPO3X+BCh +Dvkp2s85lQ/i7lUDq7V/1Badc+GpqCAoysgjh0bMSyXpPwaz3N+JhcgSEzWbXoU IlQQUWGA86jO7x0g1HBIfvmf6o+ALWKkoyLiOZ3ZgpibO/vkl+8qU6yiD+r0XDaM TTcsuRrosw6wbVsPkL7wGpTsQD1JA/FSKd7BpsQRMjxUeMtTeBtPN1o+zsvGf7he A8MYe55XXYZbHv/S9yuBCHXtCU+QRtuGJGODIPACOqsaqWETIf013sxCORAmqg3x bNEm3R0EJl3pO8Hdd2kTzIjRHgLn9LEKTIQU4+IYj0jOqXsMYjalFIL2RFC2lzI= =vgDt - -----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: http://www.auscert.org.au/render.html?cid=1980 =========================================================================== 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 iQIVAwUBUnHIsRLndAQH1ShLAQIq7g//YCzJuHO/NntgAfDnkbKvEC+S45i0qaTH 15AjIU2VWJQajVIj7vPJZdtmXqL+0Sy8l+fwvNsySlQLqTjkpHuIcyIj3LU/mvj/ mpahYgZ31lgcLTLjXML/raB/CP4es9KO4GtJuhOpdEgjYNgKLKT35ohc5WThy/i2 E+sNh4Lnv6fWPF3tzKdWcjz/a9DWtZeYBAeDXFki5pWksRlDzLl7srCWx/eZC+RI 3wULlw4JCDTbiXD90s8Csr54dCgtKSYR9bfdU2ZAZE8i8RrIgPrsznBBPpf3vBFb 5JtOuy0MWl6nTdW9Xzs6+glByZBRYD8RzSJG8ogIyNHTN208YrEV+8/f2WDwAqnY 9APdelWPvxU8bGrCgu3fCFx8YQtYI40sv2m4k3G2AvjFDv02G0Vmgq4czQHu1UIz vz4pzlgSdvyxBbG/+yLXIyn4/8OJdwWq9VXPQch/wBNRoHU7mvEaKTL1xnB24be0 GiZzb7DyN9g/a9dowa2gNNq8n+2UkJI/03Su2feB0A8byxft5J8YJg2Q1xAxug56 sRwq1OlAoe0h60UrUtqWi5aXs+NxTuaL1KSMDTnLy2r251U5JO9ZTSoaD9aG3jwT lmbx09SdCZUraCHQuvreJU0dThsdWJm+Nr7f8gimJYjqMgSoEX8+cqCZMhvw2Ddh wkzvZFI8WBc= =+3ww -----END PGP SIGNATURE-----