CVE-2026-99186

{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-99186", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-09-25T10:25:14.399Z", "datePublished": "2026-10-28T10:35:44.049Z", "dateUpdated": "2026-10-28T10:35:44.049Z"}, "containers": {"cna": {"providerMetadata": {"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-10-28T10:35:44.049Z"}, "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nx86/insn-eval: Fix shadowed segment index in get_seg_reg_override_idx()\n\nCommit 45e1dccc0653 (\"x86/insn: Simplify for_each_insn_prefix()\") made\nfor_each_insn_prefix() declare its own loop counter named idx.\nget_seg_reg_override_idx() keeps its result in a local of the same name,\nso the assignments in the loop body now write the loop counter:\n\n - the function always returns INAT_SEG_REG_DEFAULT, so FS and GS\n overrides are ignored;\n\n - a CS override sets the counter to INAT_SEG_REG_CS (2), the increment\n makes it 3, and prefixes.bytes[3] holds the last prefix, 0x2e again,\n so the loop never terminates.\n\nThe UMIP emulation reaches this from the #GP handler for user space: an\nSGDT, SIDT or SMSW with a memory operand and a CS prefix leaves the task\nspinning in the kernel, never returning to user space, with a SIGKILL\nthat is never delivered. Any user can thus tie up CPUs until reboot.\nWith an FS or GS prefix, the emulated result is written to the wrong\naddress.\n\nRename the internal macro iterator variable.\n\n[ Lukas' original patch renamed the use site, I changed it to rename the\n iterator in the macro instead, but left Lukas' commit message and\n authorship - Linus ]"}], "affected": [{"product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": ["arch/x86/include/asm/insn.h", "tools/arch/x86/include/asm/insn.h"], "versions": [{"version": "45e1dccc0653c50e377dae57ef086a8d0f71061d", "lessThan": "0efe927053f7eabd1e8658cbda96ee3d78bd1765", "status": "affected", "versionType": "git"}, {"version": "45e1dccc0653c50e377dae57ef086a8d0f71061d", "lessThan": "32c52ec87d6245ee2d12ed5dd509e40062939b50", "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/include/asm/insn.h", "tools/arch/x86/include/asm/insn.h"], "versions": [{"version": "6.19", "status": "affected"}, {"version": "0", "lessThan": "6.19", "status": "unaffected", "versionType": "semver"}, {"version": "7.2.13", "lessThanOrEqual": "7.2.*", "status": "unaffected", "versionType": "semver"}, {"version": "7.3", "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": "6.19", "versionEndExcluding": "7.2.13"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "7.3"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/0efe927053f7eabd1e8658cbda96ee3d78bd1765"}, {"url": "https://git.kernel.org/stable/c/32c52ec87d6245ee2d12ed5dd509e40062939b50"}], "title": "x86/insn-eval: Fix shadowed segment index in get_seg_reg_override_idx()", "x_generator": {"engine": "bippy-1.2.0"}}}}

{}

{"affected": [{"affectedData": [{"defaultStatus": "unaffected", "product": "Linux", "programFiles": ["arch/x86/include/asm/insn.h", "tools/arch/x86/include/asm/insn.h"], "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "vendor": "Linux", "versions": [{"lessThan": "0efe927053f7eabd1e8658cbda96ee3d78bd1765", "status": "affected", "version": "45e1dccc0653c50e377dae57ef086a8d0f71061d", "versionType": "git"}, {"lessThan": "32c52ec87d6245ee2d12ed5dd509e40062939b50", "status": "affected", "version": "45e1dccc0653c50e377dae57ef086a8d0f71061d", "versionType": "git"}]}, {"defaultStatus": "affected", "product": "Linux", "programFiles": ["arch/x86/include/asm/insn.h", "tools/arch/x86/include/asm/insn.h"], "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "vendor": "Linux", "versions": [{"status": "affected", "version": "6.19"}, {"lessThan": "6.19", "status": "unaffected", "version": "0", "versionType": "semver"}, {"lessThanOrEqual": "7.2.*", "status": "unaffected", "version": "7.2.13", "versionType": "semver"}, {"lessThanOrEqual": "*", "status": "unaffected", "version": "7.3", "versionType": "original_commit_for_fix"}]}], "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}], "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nx86/insn-eval: Fix shadowed segment index in get_seg_reg_override_idx()\n\nCommit 45e1dccc0653 (\"x86/insn: Simplify for_each_insn_prefix()\") made\nfor_each_insn_prefix() declare its own loop counter named idx.\nget_seg_reg_override_idx() keeps its result in a local of the same name,\nso the assignments in the loop body now write the loop counter:\n\n - the function always returns INAT_SEG_REG_DEFAULT, so FS and GS\n overrides are ignored;\n\n - a CS override sets the counter to INAT_SEG_REG_CS (2), the increment\n makes it 3, and prefixes.bytes[3] holds the last prefix, 0x2e again,\n so the loop never terminates.\n\nThe UMIP emulation reaches this from the #GP handler for user space: an\nSGDT, SIDT or SMSW with a memory operand and a CS prefix leaves the task\nspinning in the kernel, never returning to user space, with a SIGKILL\nthat is never delivered. Any user can thus tie up CPUs until reboot.\nWith an FS or GS prefix, the emulated result is written to the wrong\naddress.\n\nRename the internal macro iterator variable.\n\n[ Lukas' original patch renamed the use site, I changed it to rename the\n iterator in the macro instead, but left Lukas' commit message and\n authorship - Linus ]"}], "id": "CVE-2026-99186", "lastModified": "2026-10-28T11:17:39.497", "metrics": {}, "published": "2026-10-28T11:17:39.497", "references": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "url": "https://git.kernel.org/stable/c/0efe927053f7eabd1e8658cbda96ee3d78bd1765"}, {"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "url": "https://git.kernel.org/stable/c/32c52ec87d6245ee2d12ed5dd509e40062939b50"}], "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "vulnStatus": "Received"}

{"bugzilla": {"description": "kernel: kernel: Denial of Service via infinite loop in x86 instruction evaluation", "id": "2562722", "url": "https://bugzilla.redhat.com/show_bug.cgi?id=2562722"}, "csaw": false, "cvss3": {"cvss3_base_score": "5.5", "cvss3_scoring_vector": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H", "status": "draft"}, "cwe": "CWE-835", "details": ["A flaw was found in the Linux kernel's x86 instruction evaluation component. A local user can exploit this vulnerability to cause a Denial of Service (DoS) by executing instructions with segment register overrides that trigger an infinite loop during instruction decoding. This condition traps the processor core in kernel mode, tying up CPU resources until the system is rebooted. Additionally, improper segment prefix processing may cause emulated instruction results to be written to unintended memory locations."], "name": "CVE-2026-99186", "package_state": [{"cpe": "cpe:/o:redhat:enterprise_linux:10", "fix_state": "Fix deferred", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 10"}, {"cpe": "cpe:/o:redhat:enterprise_linux:6", "fix_state": "Not affected", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 6"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Fix deferred", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:7", "fix_state": "Fix deferred", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 7"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Fix deferred", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:8", "fix_state": "Fix deferred", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 8"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Fix deferred", "package_name": "kernel", "product_name": "Red Hat Enterprise Linux 9"}, {"cpe": "cpe:/o:redhat:enterprise_linux:9", "fix_state": "Fix deferred", "package_name": "kernel-rt", "product_name": "Red Hat Enterprise Linux 9"}, {"cpe": "cpe:/a:redhat:openshift:4", "fix_state": "Fix deferred", "package_name": "openshift/ose-rhel-coreos-8", "product_name": "Red Hat OpenShift Container Platform 4"}, {"cpe": "cpe:/a:redhat:openshift:4", "fix_state": "Fix deferred", "package_name": "openshift/ose-rhel-coreos-9", "product_name": "Red Hat OpenShift Container Platform 4"}, {"cpe": "cpe:/a:redhat:openshift:5", "fix_state": "Fix deferred", "package_name": "openshift/ose-rhel-coreos-10", "product_name": "Red Hat OpenShift Container Platform 5"}, {"cpe": "cpe:/a:redhat:openshift:5", "fix_state": "Fix deferred", "package_name": "openshift/ose-rhel-coreos-9", "product_name": "Red Hat OpenShift Container Platform 5"}], "public_date": "2026-10-28T10:35:44Z", "references": ["https://www.cve.org/CVERecord?id=CVE-2026-99186\nhttps://nvd.nist.gov/vuln/detail/CVE-2026-99186\nhttps://git.kernel.org/stable/c/0efe927053f7eabd1e8658cbda96ee3d78bd1765\nhttps://git.kernel.org/stable/c/32c52ec87d6245ee2d12ed5dd509e40062939b50"], "statement": "This vulnerability is rated as Moderate impact because an authenticated local unprivileged attacker can induce an infinite loop within the kernel to exhaust system CPU resources, but cannot directly escalate privileges or breach confidentiality. Exploitation occurs during user-space instruction emulation on x86 architectures when processing specific segment prefixes, resulting in core hangs that persist until the system is restarted. Because the attack vector is restricted to local access and does not allow remote exploitation, the overall operational risk remains bounded.", "threat_severity": "Moderate"}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "code_commit", "value": "[45e1dccc0653c50e377dae57ef086a8d0f71061d,0efe927053f7eabd1e8658cbda96ee3d78bd1765)"}}, {"platform": null, "status": "affected", "versions": {"scheme": "code_commit", "value": "[45e1dccc0653c50e377dae57ef086a8d0f71061d,32c52ec87d6245ee2d12ed5dd509e40062939b50)"}}], "enrichment": {"confidence": 100.0, "confidence_source": "matching", "scores": [{"score": 100.0, "source": "matching"}]}, "original": {"product": "Linux", "source": "cna", "vendor": "Linux"}, "product": "linux", "vendor": "linux"}, {"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "generic", "value": "6.19"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "generic", "value": "[0,6.19)"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "generic", "value": "[7.2.13,7.3.0)"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "generic", "value": "[7.3,*]"}}], "enrichment": {"confidence": 100.0, "confidence_source": "matching", "scores": [{"score": 100.0, "source": "matching"}]}, "original": {"product": "Linux", "source": "cna", "vendor": "Linux"}, "product": "linux", "vendor": "linux"}, {"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "code_commit", "value": "[45e1dccc0653c50e377dae57ef086a8d0f71061d,0efe927053f7eabd1e8658cbda96ee3d78bd1765)"}}, {"platform": null, "status": "affected", "versions": {"scheme": "code_commit", "value": "[45e1dccc0653c50e377dae57ef086a8d0f71061d,32c52ec87d6245ee2d12ed5dd509e40062939b50)"}}], "enrichment": {"confidence": 100.0, "confidence_source": "matching", "scores": [{"score": 100.0, "source": "matching"}]}, "original": {"product": "Linux", "source": "cna", "vendor": "Linux"}, "product": "linux_kernel", "vendor": "linux"}, {"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "generic", "value": "6.19"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "generic", "value": "[0,6.19)"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "generic", "value": "[7.2.13,7.3.0)"}}, {"platform": null, "status": "unaffected", "versions": {"scheme": "generic", "value": "[7.3,*]"}}], "enrichment": {"confidence": 100.0, "confidence_source": "matching", "scores": [{"score": 100.0, "source": "matching"}]}, "original": {"product": "Linux", "source": "cna", "vendor": "Linux"}, "product": "linux_kernel", "vendor": "linux"}], "created": "2026-10-28T12:30:17.670674+00:00", "updated": "2026-11-02T13:45:17.706808+00:00", "vendors": ["linux", "linux$PRODUCT$linux", "linux$PRODUCT$linux_kernel"], "weaknesses": ["CWE-665", "CWE-835"]}