Linux Kernel up to 6.12.82/6.18.23/6.19.13/7.0.0 MMIO Page use after free

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8.2$0-$5k0.00

Summaryinfo

A vulnerability described as critical has been identified in Linux Kernel up to 6.12.82/6.18.23/6.19.13/7.0.0. The impacted element is an unknown function of the component MMIO Page. Executing a manipulation can lead to use after free. This vulnerability is handled as CVE-2026-31588. There is not any exploit available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability was found in Linux Kernel up to 6.12.82/6.18.23/6.19.13/7.0.0. It has been declared as critical. This vulnerability affects an unknown code block of the component MMIO Page. The manipulation with an unknown input leads to a use after free vulnerability. The CWE definition for the vulnerability is CWE-416. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Use scratch field in MMIO fragment to hold small write values When exiting to userspace to service an emulated MMIO write, copy the to-be-written value to a scratch field in the MMIO fragment if the size of the data payload is 8 bytes or less, i.e. can fit in a single chunk, instead of pointing the fragment directly at the source value. This fixes a class of use-after-free bugs that occur when the emulator initiates a write using an on-stack, local variable as the source, the write splits a page boundary, *and* both pages are MMIO pages. Because KVM's ABI only allows for physically contiguous MMIO requests, accesses that split MMIO pages are separated into two fragments, and are sent to userspace one at a time. When KVM attempts to complete userspace MMIO in response to KVM_RUN after the first fragment, KVM will detect the second fragment and generate a second userspace exit, and reference the on-stack variable. The issue is most visible if the second KVM_RUN is performed by a separate task, in which case the stack of the initiating task can show up as truly freed data. ================================================================== BUG: KASAN: use-after-free in complete_emulated_mmio+0x305/0x420 Read of size 1 at addr ffff888009c378d1 by task syz-executor417/984 CPU: 1 PID: 984 Comm: syz-executor417 Not tainted 5.10.0-182.0.0.95.h2627.eulerosv2r13.x86_64 #3 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.15.0-0-g2dd4b9b3f840-prebuilt.qemu.org 04/01/2014 Call Trace: dump_stack+0xbe/0xfd print_address_description.constprop.0+0x19/0x170 __kasan_report.cold+0x6c/0x84 kasan_report+0x3a/0x50 check_memory_region+0xfd/0x1f0 memcpy+0x20/0x60 complete_emulated_mmio+0x305/0x420 kvm_arch_vcpu_ioctl_run+0x63f/0x6d0 kvm_vcpu_ioctl+0x413/0xb20 __se_sys_ioctl+0x111/0x160 do_syscall_64+0x30/0x40 entry_SYSCALL_64_after_hwframe+0x67/0xd1 RIP: 0033:0x42477d Code: <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007faa8e6890e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: ffffffffffffffda RBX: 00000000004d7338 RCX: 000000000042477d RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000005 RBP: 00000000004d7330 R08: 00007fff28d546df R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00000000004d733c R13: 0000000000000000 R14: 000000000040a200 R15: 00007fff28d54720 The buggy address belongs to the page: page:0000000029f6a428 refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x9c37 flags: 0xfffffc0000000(node=0|zone=1|lastcpupid=0x1fffff) raw: 000fffffc0000000 0000000000000000 ffffea0000270dc8 0000000000000000 raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffff888009c37780: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ffff888009c37800: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff >ffff888009c37880: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ^ ffff888009c37900: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ffff888009c37980: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ================================================================== The bug can also be reproduced with a targeted KVM-Unit-Test by hacking KVM to fill a large on-stack variable in complete_emulated_mmio(), i.e. by overwrite the data value with garbage. Limit the use of the scratch fields to 8-byte or smaller accesses, and to just writes, as larger accesses and reads are not affected thanks to implementation details in the emulator, but add a sanity check to ensure those details don't change in the future. Specifically, KVM never uses on-stack variables for accesses larger that 8 bytes, e.g. uses an operand in the emulator context, and *al ---truncated---

The advisory is shared for download at git.kernel.org. This vulnerability was named CVE-2026-31588 since 03/09/2026. The exploitation appears to be easy. There are neither technical details nor an exploit publicly available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 06/21/2026).

The vulnerability scanner Nessus provides a plugin with the ID 321690 (SUSE SLES12 Security Update : kernel (SUSE-SU-2026:2450-1)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.12.83, 6.18.24, 6.19.14 or 7.0.1 eliminates this vulnerability. Applying the patch b5a02d37eb0739f462fa12df449ab9b3480c783b/22d2ff69d487a32a8b88f9c970120fc2daa08a77/2b83d91e9ae92fe1258d7040a32430bbb3bb7d6e/3a7b6d75c8f85b09dea893f64a85a356bcf6c3fe is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at Tenable (321690) and CERT Bund (WID-SEC-2026-1279). Once again VulDB remains the best source for vulnerability data.

Affected

  • Google Container-Optimized OS
  • Debian Linux
  • Red Hat Enterprise Linux
  • Oracle Linux
  • Open Source Linux Kernel

Productinfo

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CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 8.4
VulDB Meta Temp Score: 8.2

VulDB Base Score: 8.0
VulDB Temp Score: 7.6
VulDB Vector: 🔒
VulDB Reliability: 🔍

CNA Base Score: 8.8
CNA Vector (Linux): 🔒

CVSSv2info

AVACAuCIA
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Use after free
CWE: CWE-416 / CWE-119
CAPEC: 🔒
ATT&CK: 🔒

Physical: Partially
Local: Yes
Remote: Partially

Availability: 🔒
Status: Not defined

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Nessus ID: 321690
Nessus Name: SUSE SLES12 Security Update : kernel (SUSE-SU-2026:2450-1)

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

0-Day Time: 🔒

Upgrade: Kernel 6.12.83/6.18.24/6.19.14/7.0.1
Patch: b5a02d37eb0739f462fa12df449ab9b3480c783b/22d2ff69d487a32a8b88f9c970120fc2daa08a77/2b83d91e9ae92fe1258d7040a32430bbb3bb7d6e/3a7b6d75c8f85b09dea893f64a85a356bcf6c3fe

Timelineinfo

03/09/2026 CVE reserved
04/24/2026 +45 days Advisory disclosed
04/24/2026 +0 days VulDB entry created
06/21/2026 +58 days VulDB entry last update

Sourcesinfo

Vendor: kernel.org

Advisory: git.kernel.org
Status: Confirmed

CVE: CVE-2026-31588 (🔒)
GCVE (CVE): GCVE-0-2026-31588
GCVE (VulDB): GCVE-100-359476
CERT Bund: WID-SEC-2026-1279 - Linux Kernel: Mehrere Schwachstellen

Entryinfo

Created: 04/24/2026 19:02
Updated: 06/21/2026 07:48
Changes: 04/24/2026 19:02 (58), 05/26/2026 04:39 (7), 06/03/2026 11:38 (12), 06/21/2026 07:48 (2)
Complete: 🔍
Cache ID: 216::103

Once again VulDB remains the best source for vulnerability data.

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