Vulnerabilities (CVE)

Filtered by vendor Xen Subscribe
CVE Vendors Products Updated CVSS v2 CVSS v3
CVE-2015-7504 3 Debian, Qemu, Xen 3 Debian Linux, Qemu, Xen 2020-11-16 4.6 MEDIUM 8.8 HIGH
Heap-based buffer overflow in the pcnet_receive function in hw/net/pcnet.c in QEMU allows guest OS administrators to cause a denial of service (instance crash) or possibly execute arbitrary code via a series of packets in loopback mode.
CVE-2020-25595 4 Debian, Fedoraproject, Opensuse and 1 more 4 Debian Linux, Fedora, Leap and 1 more 2020-11-11 6.1 MEDIUM 7.8 HIGH
An issue was discovered in Xen through 4.14.x. The PCI passthrough code improperly uses register data. Code paths in Xen's MSI handling have been identified that act on unsanitized values read back from device hardware registers. While devices strictly compliant with PCI specifications shouldn't be able to affect these registers, experience shows that it's very common for devices to have out-of-spec "backdoor" operations that can affect the result of these reads. A not fully trusted guest may be able to crash Xen, leading to a Denial of Service (DoS) for the entire system. Privilege escalation and information leaks cannot be excluded. All versions of Xen supporting PCI passthrough are affected. Only x86 systems are vulnerable. Arm systems are not vulnerable. Only guests with passed through PCI devices may be able to leverage the vulnerability. Only systems passing through devices with out-of-spec ("backdoor") functionality can cause issues. Experience shows that such out-of-spec functionality is common; unless you have reason to believe that your device does not have such functionality, it's better to assume that it does.
CVE-2018-15471 3 Canonical, Linux, Xen 3 Ubuntu Linux, Linux Kernel, Xen 2020-08-24 6.8 MEDIUM 7.8 HIGH
An issue was discovered in xenvif_set_hash_mapping in drivers/net/xen-netback/hash.c in the Linux kernel through 4.18.1, as used in Xen through 4.11.x and other products. The Linux netback driver allows frontends to control mapping of requests to request queues. When processing a request to set or change this mapping, some input validation (e.g., for an integer overflow) was missing or flawed, leading to OOB access in hash handling. A malicious or buggy frontend may cause the (usually privileged) backend to make out of bounds memory accesses, potentially resulting in one or more of privilege escalation, Denial of Service (DoS), or information leaks.
CVE-2019-19577 2 Fedoraproject, Xen 2 Fedora, Xen 2020-08-24 7.2 HIGH 7.2 HIGH
An issue was discovered in Xen through 4.12.x allowing x86 AMD HVM guest OS users to cause a denial of service or possibly gain privileges by triggering data-structure access during pagetable-height updates. When running on AMD systems with an IOMMU, Xen attempted to dynamically adapt the number of levels of pagetables (the pagetable height) in the IOMMU according to the guest's address space size. The code to select and update the height had several bugs. Notably, the update was done without taking a lock which is necessary for safe operation. A malicious guest administrator can cause Xen to access data structures while they are being modified, causing Xen to crash. Privilege escalation is thought to be very difficult but cannot be ruled out. Additionally, there is a potential memory leak of 4kb per guest boot, under memory pressure. Only Xen on AMD CPUs is vulnerable. Xen running on Intel CPUs is not vulnerable. ARM systems are not vulnerable. Only systems where guests are given direct access to physical devices are vulnerable. Systems which do not use PCI pass-through are not vulnerable. Only HVM guests can exploit the vulnerability. PV and PVH guests cannot. All versions of Xen with IOMMU support are vulnerable.
CVE-2019-19578 2 Fedoraproject, Xen 2 Fedora, Xen 2020-08-24 7.2 HIGH 8.8 HIGH
An issue was discovered in Xen through 4.12.x allowing x86 PV guest OS users to cause a denial of service via degenerate chains of linear pagetables, because of an incorrect fix for CVE-2017-15595. "Linear pagetables" is a technique which involves either pointing a pagetable at itself, or to another pagetable of the same or higher level. Xen has limited support for linear pagetables: A page may either point to itself, or point to another pagetable of the same level (i.e., L2 to L2, L3 to L3, and so on). XSA-240 introduced an additional restriction that limited the "depth" of such chains by allowing pages to either *point to* other pages of the same level, or *be pointed to* by other pages of the same level, but not both. To implement this, we keep track of the number of outstanding times a page points to or is pointed to another page table, to prevent both from happening at the same time. Unfortunately, the original commit introducing this reset this count when resuming validation of a partially-validated pagetable, incorrectly dropping some "linear_pt_entry" counts. If an attacker could engineer such a situation to occur, they might be able to make loops or other arbitrary chains of linear pagetables, as described in XSA-240. A malicious or buggy PV guest may cause the hypervisor to crash, resulting in Denial of Service (DoS) affecting the entire host. Privilege escalation and information leaks cannot be excluded. All versions of Xen are vulnerable. Only x86 systems are affected. Arm systems are not affected. Only x86 PV guests can leverage the vulnerability. x86 HVM and PVH guests cannot leverage the vulnerability. Only systems which have enabled linear pagetables are vulnerable. Systems which have disabled linear pagetables, either by selecting CONFIG_PV_LINEAR_PT=n when building the hypervisor, or adding pv-linear-pt=false on the command-line, are not vulnerable.
CVE-2019-18423 1 Xen 1 Xen 2020-08-24 8.5 HIGH 8.8 HIGH
An issue was discovered in Xen through 4.12.x allowing ARM guest OS users to cause a denial of service via a XENMEM_add_to_physmap hypercall. p2m->max_mapped_gfn is used by the functions p2m_resolve_translation_fault() and p2m_get_entry() to sanity check guest physical frame. The rest of the code in the two functions will assume that there is a valid root table and check that with BUG_ON(). The function p2m_get_root_pointer() will ignore the unused top bits of a guest physical frame. This means that the function p2m_set_entry() will alias the frame. However, p2m->max_mapped_gfn will be updated using the original frame. It would be possible to set p2m->max_mapped_gfn high enough to cover a frame that would lead p2m_get_root_pointer() to return NULL in p2m_get_entry() and p2m_resolve_translation_fault(). Additionally, the sanity check on p2m->max_mapped_gfn is off-by-one allowing "highest mapped + 1" to be considered valid. However, p2m_get_root_pointer() will return NULL. The problem could be triggered with a specially crafted hypercall XENMEM_add_to_physmap{, _batch} followed by an access to an address (via hypercall or direct access) that passes the sanity check but cause p2m_get_root_pointer() to return NULL. A malicious guest administrator may cause a hypervisor crash, resulting in a Denial of Service (DoS). Xen version 4.8 and newer are vulnerable. Only Arm systems are vulnerable. x86 systems are not affected.
CVE-2020-15852 2 Linux, Xen 2 Linux Kernel, Xen 2020-08-10 4.6 MEDIUM 7.8 HIGH
An issue was discovered in the Linux kernel 5.5 through 5.7.9, as used in Xen through 4.13.x for x86 PV guests. An attacker may be granted the I/O port permissions of an unrelated task. This occurs because tss_invalidate_io_bitmap mishandling causes a loss of synchronization between the I/O bitmaps of TSS and Xen, aka CID-cadfad870154.
CVE-2020-15565 2 Debian, Xen 2 Debian Linux, Xen 2020-07-27 6.1 MEDIUM 8.8 HIGH
An issue was discovered in Xen through 4.13.x, allowing x86 Intel HVM guest OS users to cause a host OS denial of service or possibly gain privileges because of insufficient cache write-back under VT-d. When page tables are shared between IOMMU and CPU, changes to them require flushing of both TLBs. Furthermore, IOMMUs may be non-coherent, and hence prior to flushing IOMMU TLBs, a CPU cache also needs writing back to memory after changes were made. Such writing back of cached data was missing in particular when splitting large page mappings into smaller granularity ones. A malicious guest may be able to retain read/write DMA access to frames returned to Xen's free pool, and later reused for another purpose. Host crashes (leading to a Denial of Service) and privilege escalation cannot be ruled out. Xen versions from at least 3.2 onwards are affected. Only x86 Intel systems are affected. x86 AMD as well as Arm systems are not affected. Only x86 HVM guests using hardware assisted paging (HAP), having a passed through PCI device assigned, and having page table sharing enabled can leverage the vulnerability. Note that page table sharing will be enabled (by default) only if Xen considers IOMMU and CPU large page size support compatible.
CVE-2017-12135 3 Citrix, Debian, Xen 3 Xenserver, Debian Linux, Xen 2020-04-14 4.6 MEDIUM 8.8 HIGH
Xen allows local OS guest users to cause a denial of service (crash) or possibly obtain sensitive information or gain privileges via vectors involving transitive grants.
CVE-2019-18422 1 Xen 1 Xen 2019-11-17 8.5 HIGH 8.8 HIGH
An issue was discovered in Xen through 4.12.x allowing ARM guest OS users to cause a denial of service or gain privileges by leveraging the erroneous enabling of interrupts. Interrupts are unconditionally unmasked in exception handlers. When an exception occurs on an ARM system which is handled without changing processor level, some interrupts are unconditionally enabled during exception entry. So exceptions which occur when interrupts are masked will effectively unmask the interrupts. A malicious guest might contrive to arrange for critical Xen code to run with interrupts erroneously enabled. This could lead to data corruption, denial of service, or possibly even privilege escalation. However a precise attack technique has not been identified.
CVE-2019-18421 1 Xen 1 Xen 2019-11-14 7.1 HIGH 7.5 HIGH
An issue was discovered in Xen through 4.12.x allowing x86 PV guest OS users to gain host OS privileges by leveraging race conditions in pagetable promotion and demotion operations. There are issues with restartable PV type change operations. To avoid using shadow pagetables for PV guests, Xen exposes the actual hardware pagetables to the guest. In order to prevent the guest from modifying these page tables directly, Xen keeps track of how pages are used using a type system; pages must be "promoted" before being used as a pagetable, and "demoted" before being used for any other type. Xen also allows for "recursive" promotions: i.e., an operating system promoting a page to an L4 pagetable may end up causing pages to be promoted to L3s, which may in turn cause pages to be promoted to L2s, and so on. These operations may take an arbitrarily large amount of time, and so must be re-startable. Unfortunately, making recursive pagetable promotion and demotion operations restartable is incredibly complicated, and the code contains several races which, if triggered, can cause Xen to drop or retain extra type counts, potentially allowing guests to get write access to in-use pagetables. A malicious PV guest administrator may be able to escalate their privilege to that of the host. All x86 systems with untrusted PV guests are vulnerable. HVM and PVH guests cannot exercise this vulnerability.
CVE-2019-17346 1 Xen 1 Xen 2019-10-25 7.2 HIGH 8.8 HIGH
An issue was discovered in Xen through 4.11.x allowing x86 PV guest OS users to cause a denial of service or gain privileges because of an incompatibility between Process Context Identifiers (PCID) and TLB flushes.
CVE-2019-17342 1 Xen 1 Xen 2019-10-25 4.4 MEDIUM 7.0 HIGH
An issue was discovered in Xen through 4.11.x allowing x86 PV guest OS users to cause a denial of service or gain privileges by leveraging a race condition that arose when XENMEM_exchange was introduced.
CVE-2019-17341 1 Xen 1 Xen 2019-10-25 6.9 MEDIUM 7.8 HIGH
An issue was discovered in Xen through 4.11.x allowing x86 PV guest OS users to cause a denial of service or gain privileges by leveraging a page-writability race condition during addition of a passed-through PCI device.
CVE-2019-17347 1 Xen 1 Xen 2019-10-25 4.6 MEDIUM 7.8 HIGH
An issue was discovered in Xen through 4.11.x allowing x86 PV guest OS users to cause a denial of service or gain privileges because a guest can manipulate its virtualised %cr4 in a way that is incompatible with Linux (and possibly other guest kernels).
CVE-2018-19962 3 Citrix, Debian, Xen 3 Xenserver, Debian Linux, Xen 2019-10-03 6.9 MEDIUM 7.8 HIGH
An issue was discovered in Xen through 4.11.x on AMD x86 platforms, possibly allowing guest OS users to gain host OS privileges because small IOMMU mappings are unsafely combined into larger ones.
CVE-2018-19961 3 Citrix, Debian, Xen 3 Xenserver, Debian Linux, Xen 2019-10-03 6.9 MEDIUM 7.8 HIGH
An issue was discovered in Xen through 4.11.x on AMD x86 platforms, possibly allowing guest OS users to gain host OS privileges because TLB flushes do not always occur after IOMMU mapping changes.
CVE-2018-14678 3 Debian, Linux, Xen 3 Debian Linux, Linux Kernel, Xen 2019-10-03 7.2 HIGH 7.8 HIGH
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.
CVE-2018-10982 2 Debian, Xen 2 Debian Linux, Xen 2019-10-03 7.2 HIGH 8.8 HIGH
An issue was discovered in Xen through 4.10.x allowing x86 HVM guest OS users to cause a denial of service (unexpectedly high interrupt number, array overrun, and hypervisor crash) or possibly gain hypervisor privileges by setting up an HPET timer to deliver interrupts in IO-APIC mode, aka vHPET interrupt injection.
CVE-2017-8905 1 Xen 1 Xen 2019-10-03 6.8 MEDIUM 8.8 HIGH
Xen through 4.6.x on 64-bit platforms mishandles a failsafe callback, which might allow PV guest OS users to execute arbitrary code on the host OS, aka XSA-215.
CVE-2017-8904 1 Xen 1 Xen 2019-10-03 6.8 MEDIUM 8.8 HIGH
Xen through 4.8.x mishandles the "contains segment descriptors" property during GNTTABOP_transfer (aka guest transfer) operations, which might allow PV guest OS users to execute arbitrary code on the host OS, aka XSA-214.
CVE-2017-8903 1 Xen 1 Xen 2019-10-03 7.2 HIGH 8.8 HIGH
Xen through 4.8.x on 64-bit platforms mishandles page tables after an IRET hypercall, which might allow PV guest OS users to execute arbitrary code on the host OS, aka XSA-213.
CVE-2017-7228 1 Xen 1 Xen 2019-10-03 7.2 HIGH 8.2 HIGH
An issue (known as XSA-212) was discovered in Xen, with fixes available for 4.8.x, 4.7.x, 4.6.x, 4.5.x, and 4.4.x. The earlier XSA-29 fix introduced an insufficient check on XENMEM_exchange input, allowing the caller to drive hypervisor memory accesses outside of the guest provided input/output arrays.
CVE-2017-12137 3 Citrix, Debian, Xen 3 Xenserver, Debian Linux, Xen 2019-10-03 7.2 HIGH 8.8 HIGH
arch/x86/mm.c in Xen allows local PV guest OS users to gain host OS privileges via vectors related to map_grant_ref.
CVE-2018-8897 8 Apple, Canonical, Citrix and 5 more 11 Mac Os X, Ubuntu Linux, Xenserver and 8 more 2019-10-03 7.2 HIGH 7.8 HIGH
A statement in the System Programming Guide of the Intel 64 and IA-32 Architectures Software Developer's Manual (SDM) was mishandled in the development of some or all operating-system kernels, resulting in unexpected behavior for #DB exceptions that are deferred by MOV SS or POP SS, as demonstrated by (for example) privilege escalation in Windows, macOS, some Xen configurations, or FreeBSD, or a Linux kernel crash. The MOV to SS and POP SS instructions inhibit interrupts (including NMIs), data breakpoints, and single step trap exceptions until the instruction boundary following the next instruction (SDM Vol. 3A; section 6.8.3). (The inhibited data breakpoints are those on memory accessed by the MOV to SS or POP to SS instruction itself.) Note that debug exceptions are not inhibited by the interrupt enable (EFLAGS.IF) system flag (SDM Vol. 3A; section 2.3). If the instruction following the MOV to SS or POP to SS instruction is an instruction like SYSCALL, SYSENTER, INT 3, etc. that transfers control to the operating system at CPL < 3, the debug exception is delivered after the transfer to CPL < 3 is complete. OS kernels may not expect this order of events and may therefore experience unexpected behavior when it occurs.
CVE-2018-7541 2 Debian, Xen 2 Debian Linux, Xen 2019-10-03 6.1 MEDIUM 8.8 HIGH
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.
CVE-2018-19966 2 Debian, Xen 2 Debian Linux, Xen 2019-10-03 7.2 HIGH 8.8 HIGH
An issue was discovered in Xen through 4.11.x allowing x86 PV guest OS users to cause a denial of service (host OS crash) or possibly gain host OS privileges because of an interpretation conflict for a union data structure associated with shadow paging. NOTE: this issue exists because of an incorrect fix for CVE-2017-15595.
CVE-2018-19963 1 Xen 1 Xen 2019-10-03 6.9 MEDIUM 7.8 HIGH
An issue was discovered in Xen 4.11 allowing HVM guest OS users to cause a denial of service (host OS crash) or possibly gain host OS privileges because x86 IOREQ server resource accounting (for external emulators) was mishandled.
CVE-2017-15590 1 Xen 1 Xen 2019-10-03 4.6 MEDIUM 8.8 HIGH
An issue was discovered in Xen through 4.9.x allowing x86 guest OS users to cause a denial of service (hypervisor crash) or possibly gain privileges because MSI mapping was mishandled.
CVE-2017-15594 1 Xen 1 Xen 2019-10-03 4.6 MEDIUM 8.8 HIGH
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.
CVE-2017-14319 1 Xen 1 Xen 2019-10-03 7.2 HIGH 8.8 HIGH
A grant unmapping issue was discovered in Xen through 4.9.x. When removing or replacing a grant mapping, the x86 PV specific path needs to make sure page table entries remain in sync with other accounting done. Although the identity of the page frame was validated correctly, neither the presence of the mapping nor page writability were taken into account.
CVE-2017-12134 2 Citrix, Xen 2 Xenserver, Xen 2019-10-03 7.2 HIGH 8.8 HIGH
The xen_biovec_phys_mergeable function in drivers/xen/biomerge.c in Xen might allow local OS guest users to corrupt block device data streams and consequently obtain sensitive memory information, cause a denial of service, or gain host OS privileges by leveraging incorrect block IO merge-ability calculation.
CVE-2017-17566 1 Xen 1 Xen 2019-10-03 6.9 MEDIUM 7.8 HIGH
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.
CVE-2017-17045 1 Xen 1 Xen 2019-10-03 7.2 HIGH 8.8 HIGH
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.
CVE-2017-15592 1 Xen 1 Xen 2019-10-03 7.2 HIGH 8.8 HIGH
An issue was discovered in Xen through 4.9.x allowing x86 HVM guest OS users to cause a denial of service (hypervisor crash) or possibly gain privileges because self-linear shadow mappings are mishandled for translated guests.
CVE-2017-12136 3 Citrix, Debian, Xen 3 Xenserver, Debian Linux, Xen 2019-05-06 6.9 MEDIUM 7.8 HIGH
Race condition in the grant table code in Xen 4.6.x through 4.9.x allows local guest OS administrators to cause a denial of service (free list corruption and host crash) or gain privileges on the host via vectors involving maptrack free list handling.
CVE-2018-18883 1 Xen 1 Xen 2019-01-24 7.2 HIGH 8.8 HIGH
An issue was discovered in Xen 4.9.x through 4.11.x, on Intel x86 platforms, allowing x86 HVM and PVH guests to cause a host OS denial of service (NULL pointer dereference) or possibly have unspecified other impact because nested VT-x is not properly restricted.
CVE-2016-1570 1 Xen 1 Xen 2018-10-30 6.9 MEDIUM 8.5 HIGH
The PV superpage functionality in arch/x86/mm.c in Xen 3.4.0, 3.4.1, and 4.1.x through 4.6.x allows local PV guests to obtain sensitive information, cause a denial of service, gain privileges, or have unspecified other impact via a crafted page identifier (MFN) to the (1) MMUEXT_MARK_SUPER or (2) MMUEXT_UNMARK_SUPER sub-op in the HYPERVISOR_mmuext_op hypercall or (3) unknown vectors related to page table updates.
CVE-2017-15595 1 Xen 1 Xen 2018-10-30 7.2 HIGH 8.8 HIGH
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.
CVE-2017-17563 1 Xen 1 Xen 2018-10-19 6.9 MEDIUM 7.8 HIGH
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.
CVE-2017-15588 1 Xen 1 Xen 2018-10-19 6.9 MEDIUM 7.8 HIGH
An issue was discovered in Xen through 4.9.x allowing x86 PV guest OS users to execute arbitrary code on the host OS because of a race condition that can cause a stale TLB entry.
CVE-2017-14316 1 Xen 1 Xen 2018-10-19 7.2 HIGH 8.8 HIGH
A parameter verification issue was discovered in Xen through 4.9.x. The function `alloc_heap_pages` allows callers to specify the first NUMA node that should be used for allocations through the `memflags` parameter; the node is extracted using the `MEMF_get_node` macro. While the function checks to see if the special constant `NUMA_NO_NODE` is specified, it otherwise does not handle the case where `node >= MAX_NUMNODES`. This allows an out-of-bounds access to an internal array.
CVE-2017-17564 1 Xen 1 Xen 2018-10-19 6.9 MEDIUM 7.8 HIGH
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.
CVE-2015-8550 2 Novell, Xen 2 Suse Linux Enterprise Real Time Extension, Xen 2017-11-04 5.7 MEDIUM 8.2 HIGH
Xen, when used on a system providing PV backends, allows local guest OS administrators to cause a denial of service (host OS crash) or gain privileges by writing to memory shared between the frontend and backend, aka a double fetch vulnerability.
CVE-2017-10922 1 Xen 1 Xen 2017-11-04 5.0 MEDIUM 7.5 HIGH
The grant-table feature in Xen through 4.8.x mishandles MMIO region grant references, which allows guest OS users to cause a denial of service (loss of grant trackability), aka XSA-224 bug 3.
CVE-2017-10916 1 Xen 1 Xen 2017-11-04 5.0 MEDIUM 7.5 HIGH
The vCPU context-switch implementation in Xen through 4.8.x improperly interacts with the Memory Protection Extensions (MPX) and Protection Key (PKU) features, which makes it easier for guest OS users to defeat ASLR and other protection mechanisms, aka XSA-220.
CVE-2017-10914 1 Xen 1 Xen 2017-11-04 6.8 MEDIUM 8.1 HIGH
The grant-table feature in Xen through 4.8.x has a race condition leading to a double free, which allows guest OS users to cause a denial of service (memory consumption), or possibly obtain sensitive information or gain privileges, aka XSA-218 bug 2.
CVE-2016-10013 1 Xen 1 Xen 2017-11-04 4.6 MEDIUM 7.8 HIGH
Xen through 4.8.x allows local 64-bit x86 HVM guest OS users to gain privileges by leveraging mishandling of SYSCALL singlestep during emulation.
CVE-2016-9380 2 Citrix, Xen 2 Xenserver, Xen 2017-07-01 4.6 MEDIUM 7.5 HIGH
The pygrub boot loader emulator in Xen, when nul-delimited output format is requested, allows local pygrub-using guest OS administrators to read or delete arbitrary files on the host via NUL bytes in the bootloader configuration file.
CVE-2016-9379 2 Citrix, Xen 2 Xenserver, Xen 2017-07-01 4.6 MEDIUM 7.9 HIGH
The pygrub boot loader emulator in Xen, when S-expression output format is requested, allows local pygrub-using guest OS administrators to read or delete arbitrary files on the host via string quotes and S-expressions in the bootloader configuration file.