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Linux Kernel EUVDEUVD-2026-39888

| CVE-2026-53283 MEDIUM
NULL Pointer Dereference (CWE-476)
2026-06-26 Linux GHSA-gv9j-3945-3x3r
Denial Of Service Linux Google Null Pointer Dereference Red Hat Canonical Amd Suse
5.5
CVSS 3.1 · NVD
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Severity by source

NVD PRIMARY
5.5 MEDIUM
AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
vuln.today AI
5.5 MEDIUM

Local vector confirmed; crash triggered at boot by hardware configuration with no confidentiality or integrity impact, only total availability loss.

3.1 AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
4.0 AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
SUSE
MEDIUM
qualitative
Red Hat
5.5 MEDIUM
qualitative

Primary rating from NVD.

CVSS VectorNVD

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

Lifecycle Timeline

5
Analysis Generated
Jul 08, 2026 - 04:24 vuln.today
CVSS changed
Jul 08, 2026 - 04:07 NVD
5.5 (MEDIUM)
Patch available
Jun 26, 2026 - 21:02 EUVD
CVE Published
Jun 26, 2026 - 19:40 nvd
MEDIUM 5.5
CVE Published
Jun 26, 2026 - 19:40 cve.org
UNKNOWN (no severity yet)

DescriptionNVD

In the Linux kernel, the following vulnerability has been resolved:

iommu/amd: Bounds-check devid in __rlookup_amd_iommu()

iommu_device_register() walks every device on the PCI bus via bus_for_each_dev() and calls amd_iommu_probe_device() for each. The inlined check_device() path computes the device's sbdf, calls rlookup_amd_iommu() to find the owning IOMMU, and only afterwards verifies devid <= pci_seg->last_bdf. __rlookup_amd_iommu() indexes rlookup_table[devid] with no bounds check of its own, so for a PCI device whose BDF is not described by the IVRS, the lookup reads past the end of the allocation before the caller's bounds check can run.

This was harmless before commit e874c666b15b ("iommu/amd: Change rlookup, irq_lookup, and alias to use kvalloc()"): the table was a zeroed page-order allocation, so the over-read returned NULL and the caller's NULL check skipped the device. After that commit the table is a tight kvcalloc() and the over-read returns adjacent slab contents, which check_device() then dereferences as a struct amd_iommu *, causing a boot-time GPF.

Seen on Google Compute Engine ct6e VMs, where the virtualized IVRS describes only the four TPU endpoints 00:04.0-07.0; the gVNIC at 00:08.0 (devid 0x40) indexes 56 bytes past the 456-byte allocation, into the adjacent kmalloc-512 slab object:

pci 0000:00:04.0: Adding to iommu group 0 pci 0000:00:05.0: Adding to iommu group 1 pci 0000:00:06.0: Adding to iommu group 2 pci 0000:00:07.0: Adding to iommu group 3 Oops: general protection fault, probably for non-canonical address 0x3a64695f78746382: 0000 [#1] SMP NOPTI CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted 6.18.22 #1 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/06/2025 RIP: 0010:amd_iommu_probe_device+0x54/0x3a0 Call Trace: __iommu_probe_device+0x107/0x520 probe_iommu_group+0x29/0x50 bus_for_each_dev+0x7e/0xe0 iommu_device_register+0xc9/0x240 iommu_go_to_state+0x9c0/0x1c60 amd_iommu_init+0x14/0x40 pci_iommu_init+0x16/0x60 do_one_initcall+0x47/0x2f0

Guard the array access in __rlookup_amd_iommu(). With the fix applied on 6.18.22, the gVNIC at 00:08.0 is skipped cleanly and the VM boots.

AnalysisAI

Boot-time kernel crash in Linux 6.16+ on AMD IOMMU-equipped systems causes a General Protection Fault when a PCI device whose Bus:Device.Function address is absent from the ACPI IVRS table is encountered during IOMMU initialization. The root cause is a missing bounds check in __rlookup_amd_iommu() that was latent until commit e874c666b15b changed the rlookup_table allocation from a zeroed page-order block (which returned NULL on overrun) to a tight kvcalloc(), causing adjacent slab contents to be dereferenced as a valid struct amd_iommu pointer. The result is a non-recoverable GPF at boot time, confirmed in production on Google Compute Engine ct6e VMs; no public exploit code and no CISA KEV listing exist at time of analysis.

Technical ContextAI

The AMD IOMMU subsystem in the Linux kernel maintains a rlookup_table array indexed by PCI device ID (devid, derived from Bus:Device.Function). During iommu_device_register(), bus_for_each_dev() walks all PCI devices and calls amd_iommu_probe_device() for each; the inlined check_device() path calls __rlookup_amd_iommu() before performing the devid <= pci_seg->last_bdf bounds check. The function unconditionally returns rlookup_table[devid] with no length guard. Prior to commit e874c666b15b, the table was a zeroed page-order allocation so an overrun produced a NULL return, which the caller's NULL check handled safely. After that commit the allocation is a precise kvcalloc(), meaning out-of-bounds reads land in an adjacent kmalloc-512 slab object whose contents are then cast and dereferenced as struct amd_iommu *, triggering a General Protection Fault. The CWE-476 (NULL Pointer Dereference) classification is slightly imprecise; the root cause is more accurately an out-of-bounds array read (CWE-125) whose garbage result is subsequently dereferenced as a pointer. The affected CPE is cpe:2.3:a:linux:linux covering kernels from the introduction of commit e874c666b15b through the fix commits.

RemediationAI

The primary fix is to upgrade to Linux 6.18.33, 7.0.10, or 7.1 (mainline), which introduce a bounds check in __rlookup_amd_iommu() before indexing rlookup_table[devid]. The upstream fix commits are available at https://git.kernel.org/stable/c/f0a0f01787ecece814414b0665df879b69849d09 (6.18 series), https://git.kernel.org/stable/c/07d0f496fe7ec5abe3bee7e38be709521567bb33 (7.0 series), and https://git.kernel.org/stable/c/79db4cbab81f07ce69a93d379ebd40d3709ecfb2. For systems that cannot be immediately patched, a targeted workaround is to disable AMD IOMMU at boot by passing the kernel parameter amd_iommu=off; this eliminates the crash but also disables IOMMU protections for DMA isolation, which may be unacceptable in security-sensitive environments. Alternatively, ensuring the ACPI IVRS table in the VM definition enumerates all PCI devices (so no devid exceeds the table bounds) prevents the overrun - cloud operators managing VM firmware or BIOS configurations may be able to apply this without a kernel upgrade. Distribution vendors including Canonical (Ubuntu) and Red Hat are expected to backport the fix; check vendor errata channels.

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Vendor StatusVendor

SUSE

Severity: Moderate
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Not-Affected
SUSE Linux Enterprise Desktop 15 SP7 Not-Affected
SUSE Linux Enterprise High Availability Extension 15 SP7 Not-Affected
SUSE Linux Enterprise High Availability Extension 15 SP7 Not-Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Not-Affected

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EUVD-2026-39888 vulnerability details – vuln.today
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