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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2014.0672 Xen Security Advisory CVE-2014-3124 / XSA-92 version 3 7 May 2014 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: Xen Publisher: Xen Operating System: Xen UNIX variants (UNIX, Linux, OSX) Impact/Access: Execute Arbitrary Code/Commands -- Existing Account Denial of Service -- Existing Account Resolution: Patch/Upgrade CVE Names: CVE-2014-3124 Original Bulletin: http://xenbits.xenproject.org/xsa/advisory-92.html - --------------------------BEGIN INCLUDED TEXT-------------------- - -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Xen Security Advisory CVE-2014-3124 / XSA-92 version 3 HVMOP_set_mem_type allows invalid P2M entries to be created UPDATES IN VERSION 3 ==================== This issue has been assigned CVE-2014-3124. ISSUE DESCRIPTION ================= The implementation in Xen of the HVMOP_set_mem_type HVM control operations attempts to exclude transitioning a page from an inappropriate memory type. However, only an inadequate subset of memory types is excluded. There are certain other types that don't correspond to a particular valid page, whose page table translation can be inappropriately changed (by HVMOP_set_mem_type) from not-present (due to the lack of valid memory page) to present. If this occurs, an invalid translation will be established. IMPACT ====== In a configuration where device models run with limited privilege (for example, stubdom device models), a guest attacker who successfully finds and exploits an unfixed security flaw in qemu-dm could leverage the other flaw into a Denial of Service affecting the whole host. In the more general case, in more abstract terms: a malicious administrator of a domain privileged with regard to an HVM guest can cause Xen to crash leading to a Denial of Service. Arbitrary code execution, and therefore privilege escalation, cannot be entirely excluded: On a system with a RAM page present immediately below the 52-bit address boundary, this would be possible. However, we are not aware of any systems with such a memory layout. VULNERABLE SYSTEMS ================== All Xen versions from 4.1 onwards are vulnerable. The vulnerability is only exposed to service domains for HVM guests which have privilege over the guest. In a usual configuration that means only device model emulators (qemu-dm). In the case of HVM guests whose device model is running in an unrestricted dom0 process, qemu-dm already has the ability to cause problems for the whole system. So in that case the vulnerability is not applicable. The situation is more subtle for an HVM guest with a stub qemu-dm. That is, where the device model runs in a separate domain (in the case of xl, as requested by "device_model_stubdomain_override=1" in the xl domain configuration file). The same applies with a qemu-dm in a dom0 process subjected to some kind kernel-based process privilege limitation (eg the chroot technique as found in some versions of XCP/XenServer). In those latter situations this issue means that the extra isolation does not provide as good a defence (against denial of service) as intended. That is the essence of this vulnerability. However, the security is still better than with a qemu-dm running as an unrestricted dom0 process. Therefore users with these configurations should not switch to an unrestricted dom0 qemu-dm. Finally, in a radically disaggregated system: where the HVM service domain software (probably, the device model domain image) is not always supplied by the host administrator, a malicious service domain administrator can exercise this vulnerability. MITIGATION ========== Running only PV guests will avoid this vulnerability. In a radically disaggregated system, restricting HVM service domains to software images approved by the host administrator will avoid the vulnerability. CREDITS ======= This issue was discovered by Jan Beulich. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. xsa92.patch xen-unstable, Xen 4.4.x, Xen 4.3.x xsa92-4.2.patch Xen 4.2.x xsa92-4.1.patch Xen 4.1.x $ sha256sum xsa92*.patch 184dcb88dfb4540fca33016ffcfe0f4f557449ab5b4ec6a4bf486c75926d23f3 xsa92.patch 76905398958dfcec98fb5bde2a68c0e86a3ccc9f442a8a658e972937fd75534a xsa92-4.1.patch bca98827834f807c787fceb6c719d9d4fe3c40786cb087156829e5e6fb5700d6 xsa92-4.2.patch $ - -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iQEcBAEBAgAGBQJTYidfAAoJEIP+FMlX6CvZ6m0H/0khx5ZZ0MiEf52szuhdBoCe zmNRuD8FrjS16CQx6KIUvvlLujWHg3hE+PFAoV3tM5U9++WrvXVO8o1ckKysle26 udRignUc1Y+Am5nB1p1KRwpVb4v8votb+/GJfFlYd01V4wyaMttQLJkI9jcLRMN7 f0bcttCZTTToQGpl6DuYh1NCOc1mLEtlC66SAHvvA8jC6K395M/MsSs+lkB63AHW SS2kdatHpt3BH4zSPRZQiwStMTCYMPN3+oc9BX1N1DphbqKo5yC1WaamF//24Ew9 ZDjtBgjQhJfZ9IKPbRctsxKOrObEfkcLLO3ETaZ74MHl94I000L+lfki7D8Gk+k= =xTcW - -----END PGP SIGNATURE----- - --------------------------END INCLUDED TEXT-------------------- You have received this e-mail bulletin as a result of your organisation's registration with AusCERT. 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On call after hours for member emergencies only. =========================================================================== -----BEGIN PGP SIGNATURE----- Comment: http://www.auscert.org.au/render.html?it=1967 iQIVAwUBU2mYkhLndAQH1ShLAQIf5A//UIwnuM5Bw6PwMEMIVs6nuSft0yh/L7qm jWHMRJW7Zc5xGBzueDNCaXYE6zbHnHa6uYHVeBNHNqC/L4OmkRI3vLfD0VfbB5EI v3TyLdfvFncVrS05VoGDgTjvs1rNeZVdLUNEKYsVu/n8ubLtGXmP8AcDpLNUultG eUe5oi8h2bqzjqzfnzhhbRp9BXWtJhj+tOMLEs0z87sPhpWJkEVIACmcMkqt+8XQ fDjpbGC2wNbMhkn7+51I1YdnolDdZq/K3aVRIKOeDedVdKO5sy5WYdwk8qncr2wY 11nQCBv6KBCmaiCpHiQzwXM/Pc86Val83nwVRDcP3cPGCQtUOB9/me3WS9SaQM8U nf6OXiMAjufrb9XjnetNWoKuCB+5zojcfJCmDpH4dzRGbDW/IrojOl3TghFqiUYX ZRs0GFmBGiw330cd5HTsF7i1yJxnb0I6ZEFTGjz4rlaz7et40+lhlf4vMPZgxuBj 8UvYR3weFSk6n0RREj6PiJMhTbeZtNjG7Iz7QD/paUFMlLY+mVXzlBGoqvnNWsu5 k6XNF3ObqbZAKinTpwcvRjEFT9Q/DNmFIjH6JGQoFCGBmo6tXWAaXAxlhHmS79Eo PVVavP1cNu7gAuqcwxoLHRsBSDT2eruBIIKWYYxY8reTpysTBUcwnEXijh2Byic8 MF+78YBhN4Y= =hR7F -----END PGP SIGNATURE-----