GLSA-202402-07 : Xen: Multiple Vulnerabilities

high Nessus Plugin ID 189976


The remote host is affected by the vulnerability described in GLSA-202402-07 (Xen: Multiple Vulnerabilities)

- grant table v2 status pages may remain accessible after de-allocation (take two) Guest get permitted access to certain Xen-owned pages of memory. The majority of such pages remain allocated / associated with a guest for its entire lifetime. Grant table v2 status pages, however, get de-allocated when a guest switched (back) from v2 to v1. The freeing of such pages requires that the hypervisor know where in the guest these pages were mapped. The hypervisor tracks only one use within guest space, but racing requests from the guest to insert mappings of these pages may result in any of them to become mapped in multiple locations. Upon switching back from v2 to v1, the guest would then retain access to a page that was freed and perhaps re-used for other purposes. This bug was fortuitously fixed by code cleanup in Xen 4.14, and backported to security-supported Xen branches as a prerequisite of the fix for XSA-378. (CVE-2021-28703)

- PoD operations on misaligned GFNs T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] x86 HVM and PVH guests may be started in populate- on-demand (PoD) mode, to provide a way for them to later easily have more memory assigned. Guests are permitted to control certain P2M aspects of individual pages via hypercalls. These hypercalls may act on ranges of pages specified via page orders (resulting in a power-of-2 number of pages). The implementation of some of these hypercalls for PoD does not enforce the base page frame number to be suitably aligned for the specified order, yet some code involved in PoD handling actually makes such an assumption. These operations are XENMEM_decrease_reservation (CVE-2021-28704) and XENMEM_populate_physmap (CVE-2021-28707), the latter usable only by domains controlling the guest, i.e. a de-privileged qemu or a stub domain.
(Patch 1, combining the fix to both these two issues.) In addition handling of XENMEM_decrease_reservation can also trigger a host crash when the specified page order is neither 4k nor 2M nor 1G (CVE-2021-28708, patch 2). (CVE-2021-28704, CVE-2021-28707, CVE-2021-28708)

- issues with partially successful P2M updates on x86 T[his CNA information record relates to multiple CVEs;
the text explains which aspects/vulnerabilities correspond to which CVE.] x86 HVM and PVH guests may be started in populate-on-demand (PoD) mode, to provide a way for them to later easily have more memory assigned. Guests are permitted to control certain P2M aspects of individual pages via hypercalls. These hypercalls may act on ranges of pages specified via page orders (resulting in a power-of-2 number of pages). In some cases the hypervisor carries out the requests by splitting them into smaller chunks. Error handling in certain PoD cases has been insufficient in that in particular partial success of some operations was not properly accounted for. There are two code paths affected - page removal (CVE-2021-28705) and insertion of new pages (CVE-2021-28709). (We provide one patch which combines the fix to both issues.) (CVE-2021-28705, CVE-2021-28709)

- guests may exceed their designated memory limit When a guest is permitted to have close to 16TiB of memory, it may be able to issue hypercalls to increase its memory allocation beyond the administrator established limit. This is a result of a calculation done with 32-bit precision, which may overflow. It would then only be the overflowed (and hence small) number which gets compared against the established upper bound. (CVE-2021-28706)

- Rejected reason: DO NOT USE THIS CANDIDATE NUMBER. ConsultIDs: none. Reason: This candidate is unused by its CNA. Notes: none. (CVE-2022-23816)

- IBPB may not prevent return branch predictions from being specified by pre-IBPB branch targets leading to a potential information disclosure. (CVE-2022-23824)

- Aliases in the branch predictor may cause some AMD processors to predict the wrong branch type potentially leading to information disclosure. (CVE-2022-23825)

- Racy interactions between dirty vram tracking and paging log dirty hypercalls Activation of log dirty mode done by XEN_DMOP_track_dirty_vram (was named HVMOP_track_dirty_vram before Xen 4.9) is racy with ongoing log dirty hypercalls. A suitably timed call to XEN_DMOP_track_dirty_vram can enable log dirty while another CPU is still in the process of tearing down the structures related to a previously enabled log dirty mode (XEN_DOMCTL_SHADOW_OP_OFF). This is due to lack of mutually exclusive locking between both operations and can lead to entries being added in already freed slots, resulting in a memory leak.

- race in VT-d domain ID cleanup Xen domain IDs are up to 15 bits wide. VT-d hardware may allow for only less than 15 bits to hold a domain ID associating a physical device with a particular domain. Therefore internally Xen domain IDs are mapped to the smaller value range. The cleaning up of the housekeeping structures has a race, allowing for VT-d domain IDs to be leaked and flushes to be bypassed.

- IOMMU: RMRR (VT-d) and unity map (AMD-Vi) handling issues T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Certain PCI devices in a system might be assigned Reserved Memory Regions (specified via Reserved Memory Region Reporting, RMRR) for Intel VT-d or Unity Mapping ranges for AMD-Vi. These are typically used for platform tasks such as legacy USB emulation. Since the precise purpose of these regions is unknown, once a device associated with such a region is active, the mappings of these regions need to remain continuouly accessible by the device. This requirement has been violated. Subsequent DMA or interrupts from the device may have unpredictable behaviour, ranging from IOMMU faults to memory corruption. (CVE-2022-26358, CVE-2022-26359, CVE-2022-26360, CVE-2022-26361)

- When SMT is enabled, certain AMD processors may speculatively execute instructions using a target from the sibling thread after an SMT mode switch potentially resulting in information disclosure. (CVE-2022-27672)

- Mis-trained branch predictions for return instructions may allow arbitrary speculative code execution under certain microarchitecture-dependent conditions. (CVE-2022-29900)

- Intel microprocessor generations 6 to 8 are affected by a new Spectre variant that is able to bypass their retpoline mitigation in the kernel to leak arbitrary data. An attacker with unprivileged user access can hijack return instructions to achieve arbitrary speculative code execution under certain microarchitecture-dependent conditions. (CVE-2022-29901)

- P2M pool freeing may take excessively long The P2M pool backing second level address translation for guests may be of significant size. Therefore its freeing may take more time than is reasonable without intermediate preemption checks. Such checking for the need to preempt was so far missing. (CVE-2022-33746)

- Arm: unbounded memory consumption for 2nd-level page tables Certain actions require e.g. removing pages from a guest's P2M (Physical-to-Machine) mapping. When large pages are in use to map guest pages in the 2nd-stage page tables, such a removal operation may incur a memory allocation (to replace a large mapping with individual smaller ones). These memory allocations are taken from the global memory pool. A malicious guest might be able to cause the global memory pool to be exhausted by manipulating its own P2M mappings.

- lock order inversion in transitive grant copy handling As part of XSA-226 a missing cleanup call was inserted on an error handling path. While doing so, locking requirements were not paid attention to. As a result two cooperating guests granting each other transitive grants can cause locks to be acquired nested within one another, but in respectively opposite order. With suitable timing between the involved grant copy operations this may result in the locking up of a CPU. (CVE-2022-33748)

- XAPI open file limit DoS It is possible for an unauthenticated client on the network to cause XAPI to hit its file-descriptor limit. This causes XAPI to be unable to accept new requests for other (trusted) clients, and blocks XAPI from carrying out any tasks that require the opening of file descriptors.

- Xenstore: Guests can crash xenstored Due to a bug in the fix of XSA-115 a malicious guest can cause xenstored to use a wrong pointer during node creation in an error path, resulting in a crash of xenstored or a memory corruption in xenstored causing further damage. Entering the error path can be controlled by the guest e.g. by exceeding the quota value of maximum nodes per domain. (CVE-2022-42309)

- Xenstore: Guests can create orphaned Xenstore nodes By creating multiple nodes inside a transaction resulting in an error, a malicious guest can create orphaned nodes in the Xenstore data base, as the cleanup after the error will not remove all nodes already created. When the transaction is committed after this situation, nodes without a valid parent can be made permanent in the data base. (CVE-2022-42310)

- Xenstore: Guests can cause Xenstore to not free temporary memory When working on a request of a guest, xenstored might need to allocate quite large amounts of memory temporarily. This memory is freed only after the request has been finished completely. A request is regarded to be finished only after the guest has read the response message of the request from the ring page. Thus a guest not reading the response can cause xenstored to not free the temporary memory. This can result in memory shortages causing Denial of Service (DoS) of xenstored. (CVE-2022-42319)

- Xenstore: Guests can get access to Xenstore nodes of deleted domains Access rights of Xenstore nodes are per domid. When a domain is gone, there might be Xenstore nodes left with access rights containing the domid of the removed domain. This is normally no problem, as those access right entries will be corrected when such a node is written later. There is a small time window when a new domain is created, where the access rights of a past domain with the same domid as the new one will be regarded to be still valid, leading to the new domain being able to get access to a node which was meant to be accessible by the removed domain. For this to happen another domain needs to write the node before the newly created domain is being introduced to Xenstore by dom0. (CVE-2022-42320)

- Xenstore: Guests can crash xenstored via exhausting the stack Xenstored is using recursion for some Xenstore operations (e.g. for deleting a sub-tree of Xenstore nodes). With sufficiently deep nesting levels this can result in stack exhaustion on xenstored, leading to a crash of xenstored. (CVE-2022-42321)

- Xenstore: Cooperating guests can create arbitrary numbers of nodes T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Since the fix of XSA-322 any Xenstore node owned by a removed domain will be modified to be owned by Dom0. This will allow two malicious guests working together to create an arbitrary number of Xenstore nodes. This is possible by domain A letting domain B write into domain A's local Xenstore tree. Domain B can then create many nodes and reboot. The nodes created by domain B will now be owned by Dom0. By repeating this process over and over again an arbitrary number of nodes can be created, as Dom0's number of nodes isn't limited by Xenstore quota. (CVE-2022-42322, CVE-2022-42323)

- Oxenstored 32->31 bit integer truncation issues Integers in Ocaml are 63 or 31 bits of signed precision.
The Ocaml Xenbus library takes a C uint32_t out of the ring and casts it directly to an Ocaml integer. In 64-bit Ocaml builds this is fine, but in 32-bit builds, it truncates off the most significant bit, and then creates unsigned/signed confusion in the remainder. This in turn can feed a negative value into logic not expecting a negative value, resulting in unexpected exceptions being thrown. The unexpected exception is not handled suitably, creating a busy-loop trying (and failing) to take the bad packet out of the xenstore ring. (CVE-2022-42324)

- Xenstore: Guests can create arbitrary number of nodes via transactions T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] In case a node has been created in a transaction and it is later deleted in the same transaction, the transaction will be terminated with an error. As this error is encountered only when handling the deleted node at transaction finalization, the transaction will have been performed partially and without updating the accounting information. This will enable a malicious guest to create arbitrary number of nodes.
(CVE-2022-42325, CVE-2022-42326)

- x86: unintended memory sharing between guests On Intel systems that support the virtualize APIC accesses feature, a guest can read and write the global shared xAPIC page by moving the local APIC out of xAPIC mode. Access to this shared page bypasses the expected isolation that should exist between two guests.

- Guests can cause Xenstore crash via soft reset When a guest issues a Soft Reset (e.g. for performing a kexec) the libxl based Xen toolstack will normally perform a XS_RELEASE Xenstore operation. Due to a bug in xenstored this can result in a crash of xenstored. Any other use of XS_RELEASE will have the same impact. (CVE-2022-42330)

- x86: speculative vulnerability in 32bit SYSCALL path Due to an oversight in the very original Spectre/Meltdown security work (XSA-254), one entrypath performs its speculation-safety actions too late.
In some configurations, there is an unprotected RET instruction which can be attacked with a variety of speculative attacks. (CVE-2022-42331)

- x86 shadow plus log-dirty mode use-after-free In environments where host assisted address translation is necessary but Hardware Assisted Paging (HAP) is unavailable, Xen will run guests in so called shadow mode.
Shadow mode maintains a pool of memory used for both shadow page tables as well as auxiliary data structures. To migrate or snapshot guests, Xen additionally runs them in so called log-dirty mode. The data structures needed by the log-dirty tracking are part of aformentioned auxiliary data. In order to keep error handling efforts within reasonable bounds, for operations which may require memory allocations shadow mode logic ensures up front that enough memory is available for the worst case requirements.
Unfortunately, while page table memory is properly accounted for on the code path requiring the potential establishing of new shadows, demands by the log-dirty infrastructure were not taken into consideration. As a result, just established shadow page tables could be freed again immediately, while other code is still accessing them on the assumption that they would remain allocated. (CVE-2022-42332)

- x86/HVM pinned cache attributes mis-handling T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] To allow cachability control for HVM guests with passed through devices, an interface exists to explicitly override defaults which would otherwise be put in place. While not exposed to the affected guests themselves, the interface specifically exists for domains controlling such guests. This interface may therefore be used by not fully privileged entities, e.g. qemu running deprivileged in Dom0 or qemu running in a so called stub-domain. With this exposure it is an issue that - the number of the such controlled regions was unbounded (CVE-2022-42333), - installation and removal of such regions was not properly serialized (CVE-2022-42334). (CVE-2022-42333, CVE-2022-42334)

- x86 shadow paging arbitrary pointer dereference In environments where host assisted address translation is necessary but Hardware Assisted Paging (HAP) is unavailable, Xen will run guests in so called shadow mode.
Due to too lax a check in one of the hypervisor routines used for shadow page handling it is possible for a guest with a PCI device passed through to cause the hypervisor to access an arbitrary pointer partially under guest control. (CVE-2022-42335)

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.


All Xen users should upgrade to the latest version:

# emerge --sync # emerge --ask --oneshot --verbose >=app-emulation/xen-4.16.6_pre1

See Also

Plugin Details

Severity: High

ID: 189976

File Name: gentoo_GLSA-202402-07.nasl

Version: 1.1

Type: local

Published: 2/4/2024

Updated: 2/4/2024

Supported Sensors: Nessus

Risk Information


Risk Factor: High

Score: 7.3


Risk Factor: Medium

Base Score: 6.9

Temporal Score: 5.1

Vector: CVSS2#AV:L/AC:M/Au:N/C:C/I:C/A:C

CVSS Score Source: CVE-2021-28709


Risk Factor: High

Base Score: 8.8

Temporal Score: 7.7

Vector: CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H

Temporal Vector: CVSS:3.0/E:U/RL:O/RC:C

CVSS Score Source: CVE-2022-42309

Vulnerability Information

CPE: p-cpe:/a:gentoo:linux:xen, cpe:/o:gentoo:linux

Required KB Items: Host/local_checks_enabled, Host/Gentoo/release, Host/Gentoo/qpkg-list

Exploit Ease: No known exploits are available

Patch Publication Date: 2/4/2024

Vulnerability Publication Date: 11/24/2021

Reference Information

CVE: CVE-2021-28703, CVE-2021-28704, CVE-2021-28705, CVE-2021-28706, CVE-2021-28707, CVE-2021-28708, CVE-2021-28709, CVE-2022-23816, CVE-2022-23824, CVE-2022-23825, CVE-2022-26356, CVE-2022-26357, CVE-2022-26358, CVE-2022-26359, CVE-2022-26360, CVE-2022-26361, CVE-2022-27672, CVE-2022-29900, CVE-2022-29901, CVE-2022-33746, CVE-2022-33747, CVE-2022-33748, CVE-2022-33749, CVE-2022-42309, CVE-2022-42310, CVE-2022-42319, CVE-2022-42320, CVE-2022-42321, CVE-2022-42322, CVE-2022-42323, CVE-2022-42324, CVE-2022-42325, CVE-2022-42326, CVE-2022-42327, CVE-2022-42330, CVE-2022-42331, CVE-2022-42332, CVE-2022-42333, CVE-2022-42334, CVE-2022-42335