An issue was discovered in Xen through 4.11.x. ARM never properly implemented grant table v2, either in the hypervisor or in Linux. Unfortunately, an ARM guest can still request v2 grant tables; they will simply not be properly set up, resulting in subsequent grant-related hypercalls hitting BUG() checks. An unprivileged guest can cause a BUG() check in the hypervisor, resulting in a denial-of-service (crash).

An issue was discovered in Xen through 4.11.x. The DEBUGCTL MSR contains several debugging features, some of which virtualise cleanly, but some do not. In particular, Branch Trace Store is not virtualised by the processor, and software has to be careful to configure it suitably not to lock up the core. As a result, it must only be available to fully trusted guests. Unfortunately, in the case that vPMU is disabled, all value checking was skipped, allowing the guest to choose any MSR_DEBUGCTL setting it likes. A malicious or buggy guest administrator (on Intel x86 HVM or PVH) can lock up the entire host, causing a Denial of Service.

An issue was discovered in the Linux kernel through 4.17.11, as used in Xen through 4.11.x. The xen_failsafe_callback entry point in arch/x86/entry/entry_64.S does not properly maintain RBX, which allows local users to cause a denial of service (uninitialized memory usage and system crash). Within Xen, 64-bit x86 PV Linux guest OS users can trigger a guest OS crash or possibly gain privileges.

Quick emulator (QEMU) before 2.8 built with the Cirrus CLGD 54xx VGA Emulator support is vulnerable to an out-of-bounds access issue. The issue could occur while copying VGA data in cirrus_bitblt_cputovideo. A privileged user inside guest could use this flaw to crash the QEMU process OR potentially execute arbitrary code on host with privileges of the QEMU process.

Quick emulator (QEMU) built with the Cirrus CLGD 54xx VGA emulator support is vulnerable to an out-of-bounds access issue. It could occur while copying VGA data via bitblt copy in backward mode. A privileged user inside a guest could use this flaw to crash the QEMU process resulting in DoS or potentially execute arbitrary code on the host with privileges of QEMU process on the host.

An issue was discovered in Xen through 4.10.x. One of the fixes in XSA-260 added some safety checks to help prevent Xen livelocking with debug exceptions. Unfortunately, due to an oversight, at least one of these safety checks can be triggered by a guest. A malicious PV guest can crash Xen, leading to a Denial of Service. All Xen systems which have applied the XSA-260 fix are vulnerable. Only x86 systems are vulnerable. ARM systems are not vulnerable. Only x86 PV guests can exploit the vulnerability. x86 HVM and PVH guests cannot exploit the vulnerability. An attacker needs to be able to control hardware debugging facilities to exploit the vulnerability, but such permissions are typically available to unprivileged users.

An issue was discovered in Xen through 4.10.x. Certain PV MMU operations may take a long time to process. For that reason Xen explicitly checks for the need to preempt the current vCPU at certain points. A few rarely taken code paths did bypass such checks. By suitably enforcing the conditions through its own page table contents, a malicious guest may cause such bypasses to be used for an unbounded number of iterations. A malicious or buggy PV guest may cause a Denial of Service (DoS) affecting the entire host. Specifically, it may prevent use of a physical CPU for an indeterminate period of time. All Xen versions from 3.4 onwards are vulnerable. Xen versions 3.3 and earlier are vulnerable to an even wider class of attacks, due to them lacking preemption checks altogether in the affected code paths. Only x86 systems are affected. ARM systems are not affected. Only multi-vCPU x86 PV guests can leverage the vulnerability. x86 HVM or PVH guests as well as x86 single-vCPU PV ones cannot leverage the vulnerability.

An issue was discovered in Xen through 4.10.x allowing x86 HVM guest OS users to cause a denial of service (host OS infinite loop) in situations where a QEMU device model attempts to make invalid transitions between states of a request.

An issue was discovered in Xen through 4.10.x allowing x86 PV guest OS users to cause a denial of service (out-of-bounds zero write and hypervisor crash) via unexpected INT 80 processing, because of an incorrect fix for CVE-2017-5754.

An issue was discovered in Xen through 4.10.x allowing guest OS users to cause a denial of service (hypervisor crash) or gain privileges by triggering a grant-table transition from v2 to v1.

An issue was discovered in Xen through 4.10.x allowing x86 PV guest OS users to cause a denial of service (host OS CPU hang) via non-preemptable L3/L4 pagetable freeing.

An issue was discovered in Xen through 4.9.x allowing PV guest OS users to cause a denial of service (host OS crash) or gain host OS privileges in shadow mode by mapping a certain auxiliary page.

An issue was discovered in Xen through 4.9.x allowing PV guest OS users to cause a denial of service (host OS crash) if shadow mode and log-dirty mode are in place, because of an incorrect assertion related to M2P.

An issue was discovered in Xen through 4.9.x allowing guest OS users to cause a denial of service (host OS crash) or gain host OS privileges by leveraging incorrect error handling for reference counting in shadow mode.

An issue was discovered in Xen through 4.9.x allowing guest OS users to cause a denial of service (host OS crash) or gain host OS privileges by leveraging an incorrect mask for reference-count overflow checking in shadow mode.

An issue was discovered in Xen through 4.9.x on the ARM platform allowing guest OS users to obtain sensitive information from DRAM after a reboot, because disjoint blocks, and physical addresses that do not start at zero, are mishandled.

An issue was discovered in Xen through 4.9.x allowing HVM guest OS users to gain privileges on the host OS, obtain sensitive information, or cause a denial of service (BUG and host OS crash) by leveraging the mishandling of Populate on Demand (PoD) Physical-to-Machine (P2M) errors.

An issue was discovered in Xen through 4.9.x allowing HVM guest OS users to cause a denial of service (infinite loop and host OS hang) by leveraging the mishandling of Populate on Demand (PoD) errors.

An issue was discovered in Xen through 4.9.x allowing x86 PV guest OS users to cause a denial of service (unbounded recursion, stack consumption, and hypervisor crash) or possibly gain privileges via crafted page-table stacking.

An issue was discovered in Xen through 4.9.x allowing x86 SVM PV guest OS users to cause a denial of service (hypervisor crash) or gain privileges because IDT settings are mishandled during CPU hotplugging.