{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-31588", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-03-09T15:48:24.120Z", "datePublished": "2026-04-24T14:42:16.288Z", "dateUpdated": "2026-08-05T12:23:39.227Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T12:23:39.227Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: x86: Use scratch field in MMIO fragment to hold small write values\n\nWhen exiting to userspace to service an emulated MMIO write, copy the\nto-be-written value to a scratch field in the MMIO fragment if the size\nof the data payload is 8 bytes or less, i.e. can fit in a single chunk,\ninstead of pointing the fragment directly at the source value.\n\nThis fixes a class of use-after-free bugs that occur when the emulator\ninitiates a write using an on-stack, local variable as the source, the\nwrite splits a page boundary, *and* both pages are MMIO pages. Because\nKVM's ABI only allows for physically contiguous MMIO requests, accesses\nthat split MMIO pages are separated into two fragments, and are sent to\nuserspace one at a time. When KVM attempts to complete userspace MMIO in\nresponse to KVM_RUN after the first fragment, KVM will detect the second\nfragment and generate a second userspace exit, and reference the on-stack\nvariable.\n\nThe issue is most visible if the second KVM_RUN is performed by a separate\ntask, in which case the stack of the initiating task can show up as truly\nfreed data.\n\n ==================================================================\n BUG: KASAN: use-after-free in complete_emulated_mmio+0x305/0x420\n Read of size 1 at addr ffff888009c378d1 by task syz-executor417/984\n\n CPU: 1 PID: 984 Comm: syz-executor417 Not tainted 5.10.0-182.0.0.95.h2627.eulerosv2r13.x86_64 #3\n Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.15.0-0-g2dd4b9b3f840-prebuilt.qemu.org 04/01/2014 Call Trace:\n dump_stack+0xbe/0xfd\n print_address_description.constprop.0+0x19/0x170\n __kasan_report.cold+0x6c/0x84\n kasan_report+0x3a/0x50\n check_memory_region+0xfd/0x1f0\n memcpy+0x20/0x60\n complete_emulated_mmio+0x305/0x420\n kvm_arch_vcpu_ioctl_run+0x63f/0x6d0\n kvm_vcpu_ioctl+0x413/0xb20\n __se_sys_ioctl+0x111/0x160\n do_syscall_64+0x30/0x40\n entry_SYSCALL_64_after_hwframe+0x67/0xd1\n RIP: 0033:0x42477d\n Code: <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48\n RSP: 002b:00007faa8e6890e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010\n RAX: ffffffffffffffda RBX: 00000000004d7338 RCX: 000000000042477d\n RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000005\n RBP: 00000000004d7330 R08: 00007fff28d546df R09: 0000000000000000\n R10: 0000000000000000 R11: 0000000000000246 R12: 00000000004d733c\n R13: 0000000000000000 R14: 000000000040a200 R15: 00007fff28d54720\n\n The buggy address belongs to the page:\n page:0000000029f6a428 refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x9c37\n flags: 0xfffffc0000000(node=0|zone=1|lastcpupid=0x1fffff)\n raw: 000fffffc0000000 0000000000000000 ffffea0000270dc8 0000000000000000\n raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000 page dumped because: kasan: bad access detected\n\n Memory state around the buggy address:\n ffff888009c37780: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff\n ffff888009c37800: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff\n >ffff888009c37880: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff\n ^\n ffff888009c37900: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff\n ffff888009c37980: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff\n ==================================================================\n\nThe bug can also be reproduced with a targeted KVM-Unit-Test by hacking\nKVM to fill a large on-stack variable in complete_emulated_mmio(), i.e. by\noverwrite the data value with garbage.\n\nLimit the use of the scratch fields to 8-byte or smaller accesses, and to\njust writes, as larger accesses and reads are not affected thanks to\nimplementation details in the emulator, but add a sanity check to ensure\nthose details don't change in the future. Specifically, KVM never uses\non-stack variables for accesses larger that 8 bytes, e.g. uses an operand\nin the emulator context, and *al\n---truncated---" } ], "metrics": [ { "cvssV3_1": { "version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H", "baseScore": 8.8, "baseSeverity": "HIGH" }, "scenarios": [ { "lang": "en", "value": "AV:L - The vulnerable path is reached through local KVM vCPU execution and KVM_RUN ioctl/MMIO emulation, not by network packets or physical attachment.\nAC:L - An attacker with KVM VM control can arrange a small write crossing two MMIO pages and issue the follow-up KVM_RUN; the needed conditions are attacker-controlled rather than environmental races.\nPR:L - The attacker needs access to create/run a KVM VM via /dev/kvm or equivalent tenant VM execution rights, but no host administrative capability check gates the vulnerable KVM_RUN path once that access exists.\nUI:N - No victim action is required after the attacker can run the crafted VM/vCPU sequence.\nS:C - KVM enforces the guest/host virtualization boundary, and exploitation of host kernel KVM state from VM execution crosses that security boundary.\nC:H - The stale MMIO fragment pointer can read freed or reused host kernel stack data and copy it into the userspace-visible MMIO data path, enabling disclosure of sensitive host kernel memory.\nI:H - This is a kernel use-after-free in KVM’s MMIO completion state machine involving freed/reused stack memory; under conservative kernel scoring, such UAF memory corruption is treated as capable of host kernel integrity compromise.\nA:H - The reported failure is a KASAN use-after-free in complete_emulated_mmio, and repeated triggering can crash or destabilize the host kernel, especially on hardened/debug or panic-on-oops deployments." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "arch/x86/kvm/x86.c", "include/linux/kvm_host.h" ], "versions": [ { "version": "f78146b0f9230765c6315b2e14f56112513389ad", "lessThan": "019d0bd32b9a4646ba35d904907452039e2db700", "status": "affected", "versionType": "git" }, { "version": "f78146b0f9230765c6315b2e14f56112513389ad", "lessThan": "4569c66dd9e94a22cd0796b6514a8b25ffff16a1", "status": "affected", "versionType": "git" }, { "version": "f78146b0f9230765c6315b2e14f56112513389ad", "lessThan": "52570e73d48f1c73836d37e594667117b4c2a5a8", "status": "affected", "versionType": "git" }, { "version": "f78146b0f9230765c6315b2e14f56112513389ad", "lessThan": "dc6a6c3db3a4eca7e747cfc46e22c08d016c68f7", "status": "affected", "versionType": "git" }, { "version": "f78146b0f9230765c6315b2e14f56112513389ad", "lessThan": "b5a02d37eb0739f462fa12df449ab9b3480c783b", "status": "affected", "versionType": "git" }, { "version": "f78146b0f9230765c6315b2e14f56112513389ad", "lessThan": "22d2ff69d487a32a8b88f9c970120fc2daa08a77", "status": "affected", "versionType": "git" }, { "version": "f78146b0f9230765c6315b2e14f56112513389ad", "lessThan": "2b83d91e9ae92fe1258d7040a32430bbb3bb7d6e", "status": "affected", "versionType": "git" }, { "version": "f78146b0f9230765c6315b2e14f56112513389ad", "lessThan": "3a7b6d75c8f85b09dea893f64a85a356bcf6c3fe", "status": "affected", "versionType": "git" }, { "version": "f78146b0f9230765c6315b2e14f56112513389ad", "lessThan": "0b16e69d17d8c35c5c9d5918bf596c75a44655d3", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "arch/x86/kvm/x86.c", "include/linux/kvm_host.h" ], "versions": [ { "version": "3.5", "status": "affected" }, { "version": "0", "lessThan": "3.5", "status": "unaffected", "versionType": "semver" }, { "version": "5.10.258", "lessThanOrEqual": "5.10.*", "status": "unaffected", "versionType": "semver" }, { "version": "5.15.209", "lessThanOrEqual": "5.15.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.1.175", "lessThanOrEqual": "6.1.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.6.136", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.83", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.18.24", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.19.14", "lessThanOrEqual": "6.19.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.0.1", "lessThanOrEqual": "7.0.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.1", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.5", "versionEndExcluding": "5.10.258" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.5", "versionEndExcluding": "5.15.209" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.5", "versionEndExcluding": "6.1.175" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.5", "versionEndExcluding": "6.6.136" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.5", "versionEndExcluding": "6.12.83" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.5", "versionEndExcluding": "6.18.24" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.5", "versionEndExcluding": "6.19.14" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.5", "versionEndExcluding": "7.0.1" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.5", "versionEndExcluding": "7.1" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/019d0bd32b9a4646ba35d904907452039e2db700" }, { "url": "https://git.kernel.org/stable/c/4569c66dd9e94a22cd0796b6514a8b25ffff16a1" }, { "url": "https://git.kernel.org/stable/c/52570e73d48f1c73836d37e594667117b4c2a5a8" }, { "url": "https://git.kernel.org/stable/c/dc6a6c3db3a4eca7e747cfc46e22c08d016c68f7" }, { "url": "https://git.kernel.org/stable/c/b5a02d37eb0739f462fa12df449ab9b3480c783b" }, { "url": "https://git.kernel.org/stable/c/22d2ff69d487a32a8b88f9c970120fc2daa08a77" }, { "url": "https://git.kernel.org/stable/c/2b83d91e9ae92fe1258d7040a32430bbb3bb7d6e" }, { "url": "https://git.kernel.org/stable/c/3a7b6d75c8f85b09dea893f64a85a356bcf6c3fe" }, { "url": "https://git.kernel.org/stable/c/0b16e69d17d8c35c5c9d5918bf596c75a44655d3" } ], "title": "KVM: x86: Use scratch field in MMIO fragment to hold small write values", "x_generator": { "engine": "bippy-1.2.0" } } } }