Summary CMPXCHG8B emulation in Xen 3.3.x through 4.7.x on x86 systems allows local HVM guest OS users to obtain sensitive information from host stack memory via a "supposedly-ignored" operand size prefix.
description Multiple vulnerabilities have been discovered in the Xen hypervisor. The Common Vulnerabilities and Exposures project identifies the following problems : CVE-2016-9932 (XSA-200) CMPXCHG8B emulation allows local HVM guest OS users to obtain sensitive information from host stack memory. CVE-2017-7995 Description Xen checks access permissions to MMIO ranges only after accessing them, allowing host PCI device space memory reads. CVE-2017-8903 (XSA-213) Xen mishandles page tables after an IRET hypercall which can lead to arbitrary code execution on the host OS. The vulnerability is only exposed to 64-bit PV guests. CVE-2017-8904 (XSA-214) Xen mishandles the 'contains segment descriptors' property during GNTTABOP_transfer. This might allow PV guest OS users to execute arbitrary code on the host OS. CVE-2017-8905 (XSA-215) Xen mishandles a failsafe callback which might allow PV guest OS users to execute arbitrary code on the host OS. For Debian 7 'Wheezy', these problems have been fixed in version 4.1.6.lts1-8. We recommend that you upgrade your xen packages. NOTE: Tenable Network Security has extracted the preceding description block directly from the DLA security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.
description The Xen Project reports : The x86 instruction CMPXCHG8B is supposed to ignore legacy operand size overrides; it only honors the REX.W override (making it CMPXCHG16B). So, the operand size is always 8 or 16. When support for CMPXCHG16B emulation was added to the instruction emulator, this restriction on the set of possible operand sizes was relied on in some parts of the emulation; but a wrong, fully general, operand size value was used for other parts of the emulation. As a result, if a guest uses a supposedly-ignored operand size prefix, a small amount of hypervisor stack data is leaked to the guests: a 96 bit leak to guests running in 64-bit mode; or, a 32 bit leak to other guests. A malicious unprivileged guest may be able to obtain sensitive information from the host.
description x86 CMPXCHG8B emulation fails to ignore operand size override [XSA-200, CVE-2016-9932] (#1404262) ---- ARM guests may induce host asynchronous abort [XSA-201, CVE-2016-9815, Note that Tenable Network Security has extracted the preceding description block directly from the Fedora update system website. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.
description x86 CMPXCHG8B emulation fails to ignore operand size override [XSA-200, CVE-2016-9932] (#1404262) ---- ARM guests may induce host asynchronous abort [XSA-201, CVE-2016-9815, CVE-2016-9816, CVE-2016-9817, CVE-2016-9818] (#1399747) qemu: Divide by zero vulnerability in cirrus_do_copy (#1399055) [CVE-2016-9921, CVE-2016-9922] Qemu: 9pfs: memory leakage via proxy/handle callbacks (#1402278) qemu ioport array overflow [XSA-199, CVE-2016-9637] Note that Tenable Network Security has extracted the preceding description block directly from the Fedora update system website. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.
description According to its self-reported version number, the Xen hypervisor installed on the remote host is missing a security update. It is, therefore, affected by an information disclosure vulnerability due to a flaw in the x86 instruction CMPXCHG8B when handling prefixes. This is triggered because legacy operand size overrides are not properly ignored. A guest attacker can exploit this issue to disclose potentially sensitive information from the hypervisor stack of the host system. Please note the following items : - Only x86 systems are affected. ARM systems are not affected. - On Xen version 4.6 and earlier, the vulnerability is exposed to all HVM guest user processes, including unprivileged processes. - On Xen version 4.7, the vulnerability is exposed only to HVM guest user processes granted a degree of privilege (e.g., direct hardware access) by the guest administrator, or else to all user processes when the VM has been explicitly configured with a non-default CPU vendor string (in xm/xl, this would be done with a 'cpuid=' domain config option). Note that Nessus has not tested for this vulnerability but has instead relied only on the changeset versions based on the xen.git change log. Nessus did not check guest hardware configurations or if patches were applied manually to the source code before a recompile and reinstall.
description The remote host is affected by the vulnerability described in GLSA-201612-56 (Xen: Multiple vulnerabilities) Multiple vulnerabilities have been discovered in Xen. Please review the CVE identifiers referenced below for details. Impact : A local attacker could possibly execute arbitrary code with the privileges of the process, could gain privileges on the host system, cause a Denial of Service condition, or obtain sensitive information. Workaround : There is no known workaround at this time.