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.

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - 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)

Note that Nessus relies on the presence of the package as reported by the vendor.

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.
    (CVE-2022-26356)

  - 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.
    (CVE-2022-26357)

  - 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.
    (CVE-2022-33747)

  - 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.
    (CVE-2022-33749)

  - 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.
    (CVE-2022-42327)

  - 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.

The remote SUSE Linux SLES11 host has packages installed that are affected by multiple vulnerabilities as referenced in the SUSE-SU-2021:14848-1 advisory.

  - Observable response discrepancy in some Intel(R) Processors may allow an authorized user to potentially     enable information disclosure via local access. (CVE-2021-0089)

  - A stack overflow via an infinite recursion vulnerability was found in the eepro100 i8255x device emulator     of QEMU. This issue occurs while processing controller commands due to a DMA reentry issue. This flaw     allows a guest user or process to consume CPU cycles or crash the QEMU process on the host, resulting in a     denial of service. The highest threat from this vulnerability is to system availability. (CVE-2021-20255)

  - x86: TSX Async Abort protections not restored after S3 This issue relates to the TSX Async Abort     speculative security vulnerability. Please see https://xenbits.xen.org/xsa/advisory-305.html for details.
    Mitigating TAA by disabling TSX (the default and preferred option) requires selecting a non-default     setting in MSR_TSX_CTRL. This setting isn't restored after S3 suspend. (CVE-2021-28690)

  - inappropriate x86 IOMMU timeout detection / handling IOMMUs process commands issued to them in parallel     with the operation of the CPU(s) issuing such commands. In the current implementation in Xen, asynchronous     notification of the completion of such commands is not used. Instead, the issuing CPU spin-waits for the     completion of the most recently issued command(s). Some of these waiting loops try to apply a timeout to     fail overly-slow commands. The course of action upon a perceived timeout actually being detected is     inappropriate: - on Intel hardware guests which did not originally cause the timeout may be marked as     crashed, - on AMD hardware higher layer callers would not be notified of the issue, making them continue     as if the IOMMU operation succeeded. (CVE-2021-28692)

  - grant table v2 status pages may remain accessible after de-allocation 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. (CVE-2021-28697)

  - long running loops in grant table handling In order to properly monitor resource use, Xen maintains     information on the grant mappings a domain may create to map grants offered by other domains. In the     process of carrying out certain actions, Xen would iterate over all such entries, including ones which     aren't in use anymore and some which may have been created but never used. If the number of entries for a     given domain is large enough, this iterating of the entire table may tie up a CPU for too long, starving     other domains or causing issues in the hypervisor itself. Note that a domain may map its own grants, i.e.
    there is no need for multiple domains to be involved here. A pair of cooperating guests may, however,     cause the effects to be more severe. (CVE-2021-28698)

  - Another race in XENMAPSPACE_grant_table handling Guests are 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, are de-allocated when a guest switches (back) from v2 to v1. Freeing     such pages requires that the hypervisor enforce that no parallel request can result in the addition of a     mapping of such a page to a guest. That enforcement was missing, allowing guests to retain access to pages     that were freed and perhaps re-used for other purposes. Unfortunately, when XSA-379 was being prepared,     this similar issue was not noticed. (CVE-2021-28701)

  - 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)

  - 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)

  - A flaw was found in the USB redirector device (usb-redir) of QEMU. Small USB packets are combined into a     single, large transfer request, to reduce the overhead and improve performance. The combined size of the     bulk transfer is used to dynamically allocate a variable length array (VLA) on the stack without proper     validation. Since the total size is not bounded, a malicious guest could use this flaw to influence the     array length and cause the QEMU process to perform an excessive allocation on the stack, resulting in a     denial of service. (CVE-2021-3527)

  - An invalid pointer initialization issue was found in the SLiRP networking implementation of QEMU. The flaw     exists in the bootp_input() function and could occur while processing a udp packet that is smaller than     the size of the 'bootp_t' structure. A malicious guest could use this flaw to leak 10 bytes of     uninitialized heap memory from the host. The highest threat from this vulnerability is to data     confidentiality. This flaw affects libslirp versions prior to 4.6.0. (CVE-2021-3592)

  - An invalid pointer initialization issue was found in the SLiRP networking implementation of QEMU. The flaw     exists in the udp_input() function and could occur while processing a udp packet that is smaller than the     size of the 'udphdr' structure. This issue may lead to out-of-bounds read access or indirect host memory     disclosure to the guest. The highest threat from this vulnerability is to data confidentiality. This flaw     affects libslirp versions prior to 4.6.0. (CVE-2021-3594)

  - An invalid pointer initialization issue was found in the SLiRP networking implementation of QEMU. The flaw     exists in the tftp_input() function and could occur while processing a udp packet that is smaller than the     size of the 'tftp_t' structure. This issue may lead to out-of-bounds read access or indirect host memory     disclosure to the guest. The highest threat from this vulnerability is to data confidentiality. This flaw     affects libslirp versions prior to 4.6.0. (CVE-2021-3595)

  - A flaw was found in the USB redirector device emulation of QEMU in versions prior to 6.1.0-rc2. It occurs     when dropping packets during a bulk transfer from a SPICE client due to the packet queue being full. A     malicious SPICE client could use this flaw to make QEMU call free() with faked heap chunk metadata,     resulting in a crash of QEMU or potential code execution with the privileges of the QEMU process on the     host. (CVE-2021-3682)

  - An off-by-one error was found in the SCSI device emulation in QEMU. It could occur while processing MODE     SELECT commands in mode_sense_page() if the 'page' argument was set to MODE_PAGE_ALLS (0x3f). A malicious     guest could use this flaw to potentially crash QEMU, resulting in a denial of service condition.
    (CVE-2021-3930)

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

ID	Name	Product	Family	Severity
250439	Linux Distros Unpatched Vulnerability : CVE-2021-28703	Nessus	Misc.	high
189976	GLSA-202402-07 : Xen: Multiple Vulnerabilities	Nessus	Gentoo Local Security Checks	high
155812	SUSE SLES11 Security Update : xen (SUSE-SU-2021:14848-1)	Nessus	SuSE Local Security Checks	high

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