{"id":"CVE-2026-99120","revision":null,"records":[{"revision":"2fd21e6566d14222a4e7a30a2b07e829","observedAt":"2026-10-28T11:27:43.363+00:00","statement":{"source":"cve-program","id":"CVE-2026-99120","aliases":[],"title":"KVM: x86/mmu: Cope with the SS bit being set in #NPF exit codes","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: x86/mmu: Cope with the SS bit being set in #NPF exit codes\n\nWhen running Hyper-V from Windows 11, KVM is seeing the SS bit set\nin nested page fault error codes produced for shadowed NPT.  The AMD\nmanual is unclear about when SS is set, including whether it can be set\nwhen SupervisorShadowStackEn (bit 6) is not set in the MISC_CTL field\nof the VMCB.\n\nNevertheless, the unexpected SS bit causes out of bounds accesses in\npermission_fault(), seen as either WARNs or UBSAN reports:\n\n  kernel: UBSAN: array-index-out-of-bounds in arch/x86/kvm/mmu.h:225:27\n  kernel: index 34 is out of range for type 'u16 [16]'\n\n(in this case, the page fault error code is 34*2=0x44, i.e. SS|U; the\nreport shows SS|U|W happening as well).  Fix the handling of unknown\nerror codes by dropping SS and (with a WARN) any bits not among those\nthat permission_fault() expects to receive.\n\nAt the same time, given the uncertainty about when hardware sets SS,\nfollow the processor's behavior when constructing the fault's error\ncode, and preserve the SS bit as passed to FNAME(walk_addr_generic).\nWhile the behavior is surprising, there's a possibility that Hyper-V\nexpects it (Hyper-V does not even enable CET unless it finds MBEC/GMET!),\nso retain the information when reflecting the fault to L1 instead of\nunconditionally discarding it.\n\nBisection shows that this started happening with commit 687ee95c1b6d (\"KVM:\nnSVM: enable GMET for guests\"), even though SHSTK was available to guests\nsince Linux 6.18.  However, this is not because bit 1 of MISC_CTL (GMET)\nsomehow enables reporting the SS bit; rather, it's simply that Hyper-V\nnever uses CET unless GMET is also present.  The WARN is reproducible\neven with gmet=0, with some hacking of kvm-unit-tests's cet.c testcase\nto ensure that the first access to the shadow stack triggers a page fault.","state":0,"publishedAt":"2026-10-28T10:34:36.224+00:00","modifiedAt":"2026-10-28T10:34:36.224+00:00","affected":[{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"product\": \"Linux\",\n                    \"vendor\": \"Linux\",\n                    \"defaultStatus\": \"unaffected\",\n                    \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n                    \"programFiles\": [\n                        \"arch/x86/kvm/mmu.h\",\n                        \"arch/x86/kvm/mmu/paging_tmpl.h\"\n                    ],\n                    \"versions\": [\n                        {\n                            \"version\": \"8db428fd5229ba509d515af10d7f33d7d4a54bfe\",\n                            \"lessThan\": \"0caeefed99b37f03251a00eb1fdb403a1cf2cb68\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"8db428fd5229ba509d515af10d7f33d7d4a54bfe\",\n                            \"lessThan\": \"d6e08ec2fff45e0ec69f11010851650d7c6282b9\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"8db428fd5229ba509d515af10d7f33d7d4a54bfe\",\n                            \"lessThan\": \"e90ab3669181c6469e3647ef2b30ae408275f496\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        }\n                    ]\n                }"},{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"product\": \"Linux\",\n                    \"vendor\": \"Linux\",\n                    \"defaultStatus\": \"affected\",\n                    \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n                    \"programFiles\": [\n                        \"arch/x86/kvm/mmu.h\",\n                        \"arch/x86/kvm/mmu/paging_tmpl.h\"\n                    ],\n                    \"versions\": [\n                        {\n                            \"version\": \"6.18\",\n                            \"status\": \"affected\"\n                        },\n                        {\n                            \"version\": \"0\",\n                            \"lessThan\": \"6.18\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.18.59\",\n                            \"lessThanOrEqual\": \"6.18.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"7.2.13\",\n                            \"lessThanOrEqual\": \"7.2.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"7.3\",\n                            \"lessThanOrEqual\": \"*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"original_commit_for_fix\"\n                        }\n                    ]\n                }"}],"metrics":[],"references":["https://git.kernel.org/stable/c/0caeefed99b37f03251a00eb1fdb403a1cf2cb68","https://git.kernel.org/stable/c/d6e08ec2fff45e0ec69f11010851650d7c6282b9","https://git.kernel.org/stable/c/e90ab3669181c6469e3647ef2b30ae408275f496"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-99120","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-99120","identifiers":["CVE-2026-99120"]},"retained":false,"historicalAffected":[]}],"coverage":[{"source":"cisa-kev:global","scope":"Complete CISA KEV catalog; all vendors. Missing entries do not establish absence of exploitation.","generation":"2026-10-31T14:05:03.5694547+00:00","complete":true,"records":1766,"lastAttemptAt":"2026-10-31T14:05:03.5694547+00:00","lastSuccessAt":"2026-10-31T14:05:03.9102612+00:00","error":null,"lastVerifiedAt":"2026-10-31T14:05:03.910611+00:00","snapshotPublishedAt":null,"importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null},{"source":"cve-program","scope":"Official CVE Program baseline and cumulative hourly delta; all vendors, published and rejected records","generation":"cve-9266d7b009bf9c4a0ccdcb5cbdea7f905cb3c4d92fd3b41581ece16b2cfdc4e7-ec769fcf6e6e34bf3f0b54e1ac62cfffb542a122ab77efcad94c9e853e0b6490","complete":true,"records":417574,"lastAttemptAt":"2026-10-31T14:05:02.6830253+00:00","lastSuccessAt":"2026-10-31T13:33:54.3368861+00:00","error":null,"lastVerifiedAt":"2026-10-31T14:05:02.6830253+00:00","snapshotPublishedAt":"2026-10-31T13:26:04+00:00","importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null},{"source":"euvd","scope":"Rolling EUVD lookups of CVE aliases in current public OSV archives; 500 identifiers per refresh, rechecked after 48 hours. Not a global EUVD catalog. Successful not-found lookups count as checked; they do not imply withdrawal or safety. No reader inventory is sent.","generation":"enrichment-1ea90a365f5b43ef9a5b92be53fe0867","complete":true,"records":13565,"lastAttemptAt":"2026-10-31T14:05:07.41688+00:00","lastSuccessAt":"2026-10-31T11:34:32.033+00:00","error":null,"lastVerifiedAt":"2026-10-31T11:34:32.033+00:00","snapshotPublishedAt":null,"importing":false,"stagedRecords":0,"checkedIdentifiers":13637,"expectedIdentifiers":13637,"failedIdentifiers":0},{"source":"first-epss:nuget","scope":"FIRST EPSS for explicit CVE aliases in the collected public NuGet archive. Not a global EPSS backfill.","generation":"2026-10-31T14:05:03.5694547+00:00","complete":true,"records":1094,"lastAttemptAt":"2026-10-31T14:05:03.5694547+00:00","lastSuccessAt":"2026-10-31T14:05:04.1115496+00:00","error":null,"lastVerifiedAt":"2026-10-31T14:05:04.11155+00:00","snapshotPublishedAt":null,"importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null},{"source":"nvd","scope":"Rolling NVD lookups of CVE aliases in current public OSV archives; 500 identifiers per refresh, rechecked after 48 hours. Not a global NVD catalog. Successful not-found lookups count as checked; they do not imply withdrawal or safety. No reader inventory is sent.","generation":"enrichment-fb26245244484b8385c58dbbcb23d928","complete":true,"records":13577,"lastAttemptAt":"2026-10-31T14:05:06.3072816+00:00","lastSuccessAt":"2026-10-31T14:05:06.296+00:00","error":null,"lastVerifiedAt":"2026-10-31T14:05:06.296+00:00","snapshotPublishedAt":null,"importing":false,"stagedRecords":0,"checkedIdentifiers":13637,"expectedIdentifiers":13637,"failedIdentifiers":0},{"source":"osv:Go","scope":"Complete OSV Go ecosystem archive, including withdrawn and malicious-package source records; statement counts are not unique CVE counts","generation":"go-21dcd6662970dfea02e4ea60ee637115e8d92664947484d2b9276b3f6568a84f","complete":true,"records":9815,"lastAttemptAt":"2026-10-31T14:05:03.2592715+00:00","lastSuccessAt":"2026-10-30T23:47:34.1817587+00:00","error":null,"lastVerifiedAt":"2026-10-31T14:05:03.2592715+00:00","snapshotPublishedAt":"2026-10-30T23:33:17+00:00","importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null},{"source":"osv:NuGet","scope":"Complete OSV NuGet ecosystem archive, including GitHub Advisory Database records; NuGet version matching only","generation":"nuget-2de9ccc5290f060c7aa63f89c25dd76f655a64ba1aba7c05c97fa3bee4f09899","complete":true,"records":1967,"lastAttemptAt":"2026-10-31T14:05:03.0514544+00:00","lastSuccessAt":"2026-10-28T20:55:34.2982937+00:00","error":null,"lastVerifiedAt":"2026-10-31T14:05:03.0514544+00:00","snapshotPublishedAt":"2026-10-28T20:03:08+00:00","importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null},{"source":"osv:crates.io","scope":"Complete OSV crates.io ecosystem archive, including withdrawn and malicious-package source records; statement counts are not unique CVE counts","generation":"crates.io-f95f76cd406ae5bae3de632ad37fd2d5160b44f5e6b51748ac6f8f0c0c88e72b","complete":true,"records":3028,"lastAttemptAt":"2026-10-31T14:05:03.3781277+00:00","lastSuccessAt":"2026-10-30T23:47:38.4914494+00:00","error":null,"lastVerifiedAt":"2026-10-31T14:05:03.3781277+00:00","snapshotPublishedAt":"2026-10-30T23:18:12+00:00","importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null},{"source":"osv:npm","scope":"Complete OSV npm ecosystem archive, including withdrawn and malicious-package source records; statement counts are not unique CVE counts","generation":"npm-d37f475fd4943f3910741120036649d396d0a133edf936fc0112d88abf9bb041","complete":true,"records":230993,"lastAttemptAt":"2026-10-31T14:05:03.1555417+00:00","lastSuccessAt":"2026-10-31T12:35:41.6420764+00:00","error":null,"lastVerifiedAt":"2026-10-31T14:05:03.1555417+00:00","snapshotPublishedAt":"2026-10-31T12:33:12+00:00","importing":false,"stagedRecords":0,"checkedIdentifiers":null,"expectedIdentifiers":null,"failedIdentifiers":null}]}