CERT RENATER
Nous contacter
- Mail : cert@support.renater.fr
- Web : Pages du CERT
- Tél : 01.53.94.20.44
- Fax : 01.53.94.20.31
=================================================================== CERT-Renater Note d'Information No. 2015/VULN240 _____________________________________________________________________ DATE : 30/10/2015 HARDWARE PLATFORM(S): / OPERATING SYSTEM(S): Systems running Xen versions 3.4 and onward. ====================================================================== http://xenbits.xen.org/xsa/advisory-148.html _____________________________________________________________________ Xen Security Advisory CVE-2015-7835 / XSA-148 version 4 x86: Uncontrolled creation of large page mappings by PV guests UPDATES IN VERSION 4 ==================== Public release. ISSUE DESCRIPTION ================= The code to validate level 2 page table entries is bypassed when certain conditions are satisfied. This means that a PV guest can create writeable mappings using super page mappings. Such writeable mappings can violate Xen intended invariants for pages which Xen is supposed to keep read-only. This is possible even if the "allowsuperpage" command line option is not used. IMPACT ====== Malicious PV guest administrators can escalate privilege so as to control the whole system. VULNERABLE SYSTEMS ================== Xen 3.4 and onward are vulnerable. Only x86 systems are vulnerable. ARM systems are not vulnerable. Only PV guests can exploit the vulnerability. Both 32-bit and 64-bit PV guests can do so. MITIGATION ========== Running only HVM guests will avoid this vulnerability. On systems where the guest kernel is controlled by the host rather than guest administrator, running only kernels which do not call these hypercalls will also prevent untrusted guest users from exploiting this issue. However untrusted guest administrators can still trigger it unless further steps are taken to prevent them from loading code into the kernel (e.g. by disabling loadable modules etc) or from using other mechanisms which allow them to run code at kernel privilege. CREDITS ======= This issue was discovered by ??? (??) of Alibaba. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. xsa148.patch xen-unstable, Xen 4.6.x xsa148-4.5.patch Xen 4.5.x xsa148-4.4.patch Xen 4.4.x, Xen 4.3.x $ sha256sum xsa148*.patch f320d105a4832124910f46c50acd4803fe289bd7c4702ec15f97fb611b70944d xsa148.patch 7f78efd001f041a0e5502546664d28011cb881d72c94ea564585efb3ca01ddfe xsa148-4.4.patch 272a729048471cea851d4a881f3f2c32c7be101e2a452d2b2ceb9d66908ee4a3 xsa148-4.5.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 ========================================================= Serveur de référence du CERT-Renater https://services.renater.fr/ssi/ ========================================================== + CERT-RENATER | tel : 01-53-94-20-44 + + 23 - 25 Rue Daviel | fax : 01-53-94-20-41 + + 75013 Paris | email: cert@support.renater.fr + ========================================================== [An attachment of type application/pkcs7-signature was included here]