High Memory corruption

CVE-2026-31588 — KVM: x86: Use scratch field in MMIO fragment to hold small write values

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---

Published Apr 24, 2026 · Updated Oct 13, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: Linux

Low

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.

How the score was calculated

EPSS 0.2% (30-day exploitation probability)+1
Technical severity (high)+6

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation

Not confirmed

Not in CISA KEV — an absence of record, not proof it is unexploited.

EPSS FIRST

0.19%

ahead of 8% of scored CVEs · Oct 15, 2026

Affects

Linux

Linux and 1 more

CVSS base

8.8

High · 2 source(s)

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

Documented patch — git.kernel.org (NIST National Vulnerability Database)
Documented patch — git.kernel.org (NIST National Vulnerability Database)
Documented patch — git.kernel.org (NIST National Vulnerability Database)
Documented patch — git.kernel.org (NIST National Vulnerability Database)
Documented patch — git.kernel.org (NIST National Vulnerability Database)
Documented patch — git.kernel.org (NIST National Vulnerability Database)

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (Linux Linux, Linux Linux Kernel).
Apply the fixed version or the patch documented under Remediation.
Search available logs for exploit probes matching the vulnerability class (memory corruption), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
Linux	Linux	≥ f78146b0f9230765c6315b2e14f56112513389ad and < 019d0bd32b9a4646ba35d904907452039e2db700≥ f78146b0f9230765c6315b2e14f56112513389ad and < 4569c66dd9e94a22cd0796b6514a8b25ffff16a1≥ f78146b0f9230765c6315b2e14f56112513389ad and < 52570e73d48f1c73836d37e594667117b4c2a5a8≥ f78146b0f9230765c6315b2e14f56112513389ad and < dc6a6c3db3a4eca7e747cfc46e22c08d016c68f7≥ f78146b0f9230765c6315b2e14f56112513389ad and < b5a02d37eb0739f462fa12df449ab9b3480c783b≥ f78146b0f9230765c6315b2e14f56112513389ad and < 22d2ff69d487a32a8b88f9c970120fc2daa08a77≥ f78146b0f9230765c6315b2e14f56112513389ad and < 2b83d91e9ae92fe1258d7040a32430bbb3bb7d6e≥ f78146b0f9230765c6315b2e14f56112513389ad and < 3a7b6d75c8f85b09dea893f64a85a356bcf6c3fe and 2 more ≥ f78146b0f9230765c6315b2e14f56112513389ad and < 0b16e69d17d8c35c5c9d5918bf596c75a44655d3version 3.5	Vulnerable	CVE Program (cve.org) e CISA ADP
Linux	Linux Kernel	≥ 3.5 and < 6.6.136≥ 6.7 and < 6.12.83≥ 6.13 and < 6.18.24≥ 6.19 and < 6.19.14≥ 7.0 and < 7.0.1	Vulnerable	NIST National Vulnerability Database

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector

Local

Attack complexity

Low

Privileges required

Low

User interaction

None

Scope

Changed

Confidentiality

High

Integrity

High

Availability

High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Scored by
8.8	CVSS 3.1	High	2.0	6.0	416baaa9-dc9f-4396-8d5f-8c081fb06d67 via NIST National Vulnerability Database
8.8	CVSS 3.1	High	—	—	Linux via CVE Program (cve.org) e CISA ADP

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H (score shown at the top: 416baaa9-dc9f-4396-8d5f-8c081fb06d67)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-416 · Use After Free

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 15, 2026 · 3 reading(s) · max 0.19%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

Local/physical vector: focus on endpoint telemetry (EDR) from affected hosts.
Correlate service crashes/restarts with inbound traffic; repeated crashes may indicate attempts.

endpoint telemetry (EDR)crash dumps

Timeline

What happened to this CVE, newest first.

2026
Affected products added · linux/linux
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
Record published
Oct 13, 2026
Fix documented
Oct 13, 2026 · NIST National Vulnerability Database
CVSS changed · 8.8
Oct 13, 2026 · NIST National Vulnerability Database
Source status changed · → Modified
Oct 13, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 13, 2026 · NIST National Vulnerability Database
CVE published
Apr 24, 2026 · Linux

Source activity

Repeated readings are counted rather than listed.

1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

9 on the record

git.kernel.org/stable/c/22d2ff69d487a32a8b88f9c970120fc2daa08a77
Patch, NIST National Vulnerability Database
git.kernel.org/stable/c/0b16e69d17d8c35c5c9d5918bf596c75a44655d3
Patch, NIST National Vulnerability Database
git.kernel.org/stable/c/3a7b6d75c8f85b09dea893f64a85a356bcf6c3fe
Patch, NIST National Vulnerability Database
git.kernel.org/stable/c/dc6a6c3db3a4eca7e747cfc46e22c08d016c68f7
Patch, NIST National Vulnerability Database
git.kernel.org/stable/c/b5a02d37eb0739f462fa12df449ab9b3480c783b
Patch, NIST National Vulnerability Database
git.kernel.org/stable/c/2b83d91e9ae92fe1258d7040a32430bbb3bb7d6e
Patch, NIST National Vulnerability Database
git.kernel.org/stable/c/019d0bd32b9a4646ba35d904907452039e2db700
NIST National Vulnerability Database
git.kernel.org/stable/c/52570e73d48f1c73836d37e594667117b4c2a5a8
NIST National Vulnerability Database
git.kernel.org/stable/c/4569c66dd9e94a22cd0796b6514a8b25ffff16a1
NIST National Vulnerability Database

Elsewhere on this site

Linux
every CVE for this vendor

Memory corruption
same class

CWE-416
other pages naming this weakness

Related CVEs (same products)

Critical CVE-2026-99999 ipv4: validate checksum_start before completing checksum 15h
Unknown CVE-2026-98432 ipv4: free inet_opt and ireq_opt after an RCU grace period 15h
Unknown CVE-2026-98424 wifi: cfg80211: undo netns switch if renaming the wiphy fails 1d
Unknown CVE-2026-98425 wifi: mac80211: don't warn when an IBSS has no channel to scan 1d
Unknown CVE-2026-98426 wifi: mwifiex: fix IRQ leak using wrong index in MSI-X error path 1d
Unknown CVE-2026-98427 net/sched: codel: bound the dropping loop per dequeue call 1d

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No CISA SSVC assessment.
No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-31588 is "KVM: x86: Use scratch field in MMIO fragment to hold small write values", rated High. It affects Linux (Linux); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 8.8 describes technical severity. EPSS 0.19% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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