tapdisk: Out-of-bounds access in tap_ctl_connect_xenblkif()

ISSUE DESCRIPTION Tapdisk is a userspace xen-blkback implementation used by the XAPI toolstack. During connection, multi-page rings may be negotiated between the frontend and backend. Tapdisk had no boundary check on the size requested by the frontend, and assumed it did not exceed 8. IMPACT A...

x86/AMD: ineffectual Zenbleed workaround

ISSUE DESCRIPTION The workaround for XSA-433 Zenbleed, CVE-2023-20593 was later re-worked to better integrate with other manipulations of the same MSR. In this rework an inverted conditional was introduced, resulting in the workaround to not be applied when needed and vice versa. For more details...

gnttab: cache-flush handling may cause page reference leak

ISSUE DESCRIPTION With its original introduction, GNTTABcacheflush was made available uniformly. XSA-232 CVE-2017-14318 then covered an omitted NULL pointer check, yet the addition of that check failed to adjust the subsequent error path. That error path fails to drop a page reference in case the...

VMX: VMentry failure with branch tracing and blocked states

ISSUE DESCRIPTION For XSA-308 logic was introduced, as VMX VMEntry checks do not like the exact combination of state which occurs when DB in intercepted, Single Stepping is active, and blocked by STI/MovSS is active, despite this being a legitimate state to be in. The resulting VMEntry failure is...

grant-table: double version change race

ISSUE DESCRIPTION XSA-501 was about issues with v1 - v2 and v2 - v1 changes racing certain other grant table operations. Sadly a v2 - v1 - v2 change has yet another effect which wasn't accounted for: During the first change, status pages would be freed. During the second change they would be...

Arm: multiple issues with GNTTABOP_cache_flush

ISSUE DESCRIPTION 1 XSA-437 CVE-2023-34321 addressed issues with overflows in calculations involved in guests flushing caches through GNTTABOPcacheflush. Unfortunately the fix there introduced a calculation which may underflow, resulting in a loop which would - at least on 64-bit Arm - take...

Xenstore: Guests can crash xenstored during Live Update

ISSUE DESCRIPTION During Xenstore live update the state record for a Xenstore watch with specified watch depth is written with two bytes missing. This results in an inconsistent state when reading the state back in the new Xenstore, causing a crash of Xenstore or wrong Xenstore data. IMPACT An...

x86: XPTI may break on huge-memory systems

ISSUE DESCRIPTION XPTI Xen Page Table Isolation was introduced to mitigate Meltdown CVE-2017-5754, one aspect of XSA-254. This involves copying 64-bit PV guest page table entries from guest-chosen root page tables to the Xen- chosen one which is in actual use by hardware. To read the guest root...

Linux xen-netfront: backend can crash guest via malformed RX packets

ISSUE DESCRIPTION If a RX packet sent from the networking backend to the Linux xen-netfront driver is split into multiple slots and the first slot is shorter than an Ethernet header, a BUG will crash the guest. This is a backend induced Denial of Service DoS. IMPACT A malicious network backend ca...

Unconditionally do TLB flushing ahead of page scrubbing

ISSUE DESCRIPTION x86 PV guests can free memory pages while still keeping a stale TLB entry pointing to them. A TLB flush is only issued by Xen if needed when the page is re-used. Since it's possible for the page to be scrubbed ahead of the TLB flush, there's a window where a PV guest can modify ...

oxenstored: Unbounded accumulation of watches

ISSUE DESCRIPTION Oxenstored maintains two datastructures about watches; one global trie, and one hashtable tracked per domain. When a xenbus reconnect is requested, watches are not cleared out of the global trie. IMPACT A guest can cause unbounded memory usage in oxenstored. This can lead to a...

x86: DMs may cause mem leak by IRQ binding

ISSUE DESCRIPTION When guests are terminated, various pieces of cleanup need carrying out. The cleaning up of PCI devices which were assigned to guests, and the associated removal of tracking structures for IRQs used by the devices occurs relatively early in the process. Unfortunately after that...

Out-of-bounds accesses in Tapdisk

ISSUE DESCRIPTION Tapdisk is a userspace xen-blkback implementation used by the XAPI toolstack. Several bounds checks have been found to be incorrect. There is no upper bounds check for blkif-lastsect. Passing a value larger than 7 will result in a read or write beyond the mapped grant. This is...

x86: improper handling of HVM emulation return codes

ISSUE DESCRIPTION A guest with a PCI device assigned that has at least a BAR on the IO port space can trigger a BUG in Xen. IMPACT Passing through a PCI device with at least one BAR in IO address space to unprivileged HVM guests can result in a Denial of Service DoS affecting the entire host...

correct buffer checks for DM_OP hypercalls

ISSUE DESCRIPTION Parts of the DMOP handling code assumes the caller has provided the required number of buffers for the given operation without any checking being done. As a result, certain operations might access stack rubble as structures are possibly uninitialized. IMPACT A device model of a...

pygrub is only supported in de-privileged mode

ISSUE DESCRIPTION XSA-443 and XSA-497 addressed specific issues in specific file system drivers libfsimage used by pygrub. Further issues were reported, and yet more are to be expected. XSA-443 introduced a means to run pygrub de-privileged. Only this mode of operation is security supported from...

evtchn: Race between FIFO expand and reset

ISSUE DESCRIPTION The EVTCHNOPexpandarray hypercall checks for whether FIFO event channels are enabled, but without holding the correct lock. It can race with EVTCHNOPreset, resulting in dereferencing a NULL pointer. IMPACT A malicious HVM guest x86 HVM or PVH, and ARM can crash Xen leading to a...

PoD: Don't try to reclaim special pages

ISSUE DESCRIPTION A guest started with Populated on Demand enabled PoD can attempt to reclaim pages which aren't regular guest RAM. This can cause corruption of memory management state in Xen. IMPACT A buggy or malicious guest can cause corruption of Xen's state, leading to crashes or other...

grant-table: type confusion in grant-copy

ISSUE DESCRIPTION When grant-copy operations are processed, the respective grant may or may not already be in use by another operation a mapping or another copy. For all copy operations the referenced guest frame is looked up. When another operation is already active for the grant the grant is...

vNUMA domain cleanup may race other operations

ISSUE DESCRIPTION Accessing the vNUMA configuration data of a guest is still possible when domain destruction has already started. The cleaning up of that configuration information is not synchronized with its retrieval by a device model controlling the guest. IMPACT While Denial of Service DoS...

Viridian STIMER division by zero

ISSUE DESCRIPTION The logic to handle periodic Viridian STIMERs performs a division with an unchecked user-controlled divisor value, that can be set to zero to cause a DE fault. IMPACT Enabling Viridian STIMERs to unprivileged HVM guests can result in a Denial of Service DoS affecting the entire...

grant-table: version change racing with other operations

ISSUE DESCRIPTION With the introduction of Grant Table v2 came the requirement to be able to switch between versions. Switching from v1 to v2 reduces the number of valid grant references, as a bigger shared entry structure is then needed while the shared table doesn't change size. Switching from ...

sysctl and platform-op locks open to abuse

ISSUE DESCRIPTION To manage the system, sysctl and platform operations are used by the control domain or a possible Xenstore domain. Some of these operations may not be executed in parallel, so a system-wide lock each is used. The way those locks are acquired is, however, not providing any...

x86: Out-of-bounds read in vRTC emulation

ISSUE DESCRIPTION Accesses to the CMOS memory contents are done using an indirect IO port pair. Therefore Xen needs to cache the guest chosen index, and one of the usages of the index didn't take the necessary locking to avoid concurrent changes. As a result, a guest could change the index after ...

buffer overruns in libfsimage iso9660 handling

ISSUE DESCRIPTION The directory and Rock Ridge / SUSP walk in libfsimage's iso9660 driver derives several lengths directly from attacker-controlled on-disk fields without validating them: The directory loop itself assumes a good record length. This is CVE-2026-42494. The calculation of the System...

vIRQ event channel binding may break Xenstore

ISSUE DESCRIPTION Xenstore, to have an up-to-date picture of the entire system, wants to know of domains appearing and disappearing. To make this more robust, a new XENDOMCTLgetdomainstate was introduced. The management of the bitmap underlying that operation is tied into the binding of the...

x86 shadow paging is deprecated

ISSUE DESCRIPTION Addressing certain issues, in particular related to operations which may take excessively long and therefore would need preemption, has turned out overly costly. Since alternatives HVM/PVH: HAP, PV: shim are commonly available, the decision was to deprecate the functionality,...

XAPI: Missing TLS verification in some SDKs

ISSUE DESCRIPTION XAPI provides SDKs; bindings for the API in various programming languages. These are artefacts from a build of XAPI, intended for integration into 3rd party products. In all SDKs, there is a main RPC connection to the XAPI host. TLS for this connection is verified properly, or...

x86: mismatched mapcache metadata

ISSUE DESCRIPTION Some shadow paging errors paths will switch the page-tables without updating the currently running vCPU reference. This causes a mismatch between the loaded page-tables and the mapcache metadata which can lead to corruption of the mapcache. IMPACT Privilege escalation, Denial of...

x86 HVM I/O port list traversal

ISSUE DESCRIPTION HVM guest I/O port accesses are subject to either emulation or at least translation. Translations are managed by the device model via XENDOMCTLioportmapping, and hence the linked list used may changed at any time. Traversal of those lists while handling guest I/O port accesses...

domctl lock open to abuse

ISSUE DESCRIPTION To create and manage guests, domctl operations are used by the control domain, a possible Xenstore domain, or by a domain controlling a particular guest. Some of these operations may not be executed in parallel, so a system-wide lock is used. The way that lock is acquired is,...

Arm: Completion of memory accesses not guaranteed by completion of a TLBI

ISSUE DESCRIPTION A hardware issue has been identified in certain Arm CPU designs. A broadcast TLBI on one PE may complete before affected memory accesses on another PE are globally observed. This may permit bypass of Stage 1 translation, Stage 2 translation, or GPT protection. The erratum occurs...

x86: CPU Opcode Cache corruption

ISSUE DESCRIPTION AMD have disclosed a potential vulnerability in certain CPUs which can cause instructions to execute at a higher privilege. For more information, see: https://www.amd.com/en/resources/product-security/bulletin/amd-sb-7052.html IMPACT Code of any privilege could escalate to a...

Multiple RBAC issues in XAPI

ISSUE DESCRIPTION XAPI can configure different users with different roles, using Role Based Access Control. For more details, see: https://docs.xenserver.com/en-us/xencenter/current-release/rbac-overview.htmlrbac-roles The pool-admin role is fully privileged. Notably, users with this role can als...

grant table v2 race in status page mapping

ISSUE DESCRIPTION The adjustments made for XSA-379 as well as those subsequently becoming XSA-387 still left a race window, when a HVM or PVH guest does a grant table version change from v2 to v1 in parallel with mapping the status pages via XENMEMaddtophysmap. Some of the status pages may then b...

Linux kernel out of bounds read via Xen-related sysfs file

ISSUE DESCRIPTION The Linux sysfs file /sys/hypervisor/properties/buildid does not contain printable information, but a binary value of typically 16 or 20 bytes, which is not terminated by a zero byte. The kernel driver making this information available is using the sprintf function for writing t...

oxenstored keeps quota related use counts across domain destruction

ISSUE DESCRIPTION When oxenstored is tearing a domain down, the node data is cleaned up but the usage counts are leaked. When the domain ID is eventually reused, the new domain can create fewer nodes before beeing deemed to be over quota. IMPACT Over an extended period of time, new domains will b...

Xenstored DoS via XS_RESET_WATCHES command

ISSUE DESCRIPTION Any guest can cause xenstored to crash by issuing a XSRESETWATCHES command within a transaction due to an assert triggering. In case xenstored was built with NDEBUG defined nothing bad will happen, as assert is doing nothing in this case. Note that the default is not to define...

Linux kernel double free in Xen privcmd driver

ISSUE DESCRIPTION The Linux kernel's privcmd driver can be abused to circumvent kernel lockdown secure boot by causing a double free of kernel memory. Note that this operation can be performed by root only, so any further impact on the system like denial of service is not security relevant. IMPAC...

x86: Floating Point Divider State Sampling

ISSUE DESCRIPTION Researchers from the CISPA Helmholtz Center for Information Security have discovered Floating Point Divider State Sampling. It is detailed in a paper titled "TREVEX: A Black-Box Detection Framework For Data-Flow Transient Execution Vulnerabilities" For more information, see:...

Linux privcmd driver can circumvent kernel lockdown

ISSUE DESCRIPTION The Linux kernel's privcmd driver can be abused to circumvent kernel lockdown secure boot, e.g. by modifying page tables to enable user mode to modify kernel memory. IMPACT An administrator of an unprivileged guest booted in secure mode is able to perform actions on the kernel...

Use after free of paging structures in EPT

ISSUE DESCRIPTION The Intel EPT paging code uses an optimization to defer flushing of any cached EPT state until the p2m lock is dropped, so that multiple modifications done under the same locked region only issue a single flush. Freeing of paging structures however is not deferred until the...

Xenstored DoS by unprivileged domain

ISSUE DESCRIPTION Any guest issuing a Xenstore command accessing a node using the illegal node path "/local/domain/", will crash xenstored due to a clobbered error indicator in xenstored when verifying the node path. Note that the crash is forced via a failing assert statement in xenstored. In ca...

x86: incomplete IBPB for vCPU isolation

ISSUE DESCRIPTION In the context switch logic Xen attempts to skip an IBPB in the case of a vCPU returning to a CPU on which it was the previous vCPU to run. While safe for Xen's isolation between vCPUs, this prevents the guest kernel correctly isolating between tasks. Consider: 1 vCPU runs on CP...

x86: buffer overrun with shadow paging + tracing

ISSUE DESCRIPTION Shadow mode tracing code uses a set of per-CPU variables to avoid cumbersome parameter passing. Some of these variables are written to with guest controlled data, of guest controllable size. That size can be larger than the variable, and bounding of the writes was missing. IMPAC...

varstored: TOCTOU issues with mapped guest memory

ISSUE DESCRIPTION varstored is a component of the Xapi toolstack handling UEFI Variables for a VM. It has a communication path with OVMF inside the VM involving mapping a buffer prepared by OVMF. Within varstored, there were insufficient compiler barriers, creating TOCTOU issues with data in the...

Incorrect removal of permissions on PCI device unplug

ISSUE DESCRIPTION When passing through PCI devices, the detach logic in libxl won't remove access permissions to any 64bit memory BARs the device might have. As a result a domain can still have access any 64bit memory BAR when such device is no longer assigned to the domain. For PV domains the...

x86: Incorrect input sanitisation in Viridian hypercalls

ISSUE DESCRIPTION Some Viridian hypercalls can specify a mask of vCPU IDs as an input, in one of three formats. Xen has boundary checking bugs with all three formats, which can cause out-of-bounds reads and writes while processing the inputs. CVE-2025-58147. Hypercalls using the HVVPSET Sparse...

XAPI UTF-8 string handling

ISSUE DESCRIPTION There are multiple issues. 1. Updates to the XAPI database sanitise input strings, but try generating the notification using the unsanitised input. This causes the database's event thread to terminate and cease further processing. 2. XAPI's UTF-8 encoder implements v3.0 of the...

Mutiple vulnerabilities in the Viridian interface

ISSUE DESCRIPTION There are multiple issues related to the handling and accessing of guest memory pages in the viridian code: 1. A NULL pointer dereference in the updating of the reference TSC area. This is CVE-2025-27466. 2. A NULL pointer dereference by assuming the SIM page is mapped when a...