CVE-2026-99186 (GCVE-0-2026-99186)

Vulnerability from cvelistv5 – Published: 2026-10-28 10:35 – Updated: 2026-10-28 10:35
VLAI
Title
x86/insn-eval: Fix shadowed segment index in get_seg_reg_override_idx()
Summary
In the Linux kernel, the following vulnerability has been resolved: x86/insn-eval: Fix shadowed segment index in get_seg_reg_override_idx() Commit 45e1dccc0653 ("x86/insn: Simplify for_each_insn_prefix()") made for_each_insn_prefix() declare its own loop counter named idx. get_seg_reg_override_idx() keeps its result in a local of the same name, so the assignments in the loop body now write the loop counter: - the function always returns INAT_SEG_REG_DEFAULT, so FS and GS overrides are ignored; - a CS override sets the counter to INAT_SEG_REG_CS (2), the increment makes it 3, and prefixes.bytes[3] holds the last prefix, 0x2e again, so the loop never terminates. The UMIP emulation reaches this from the #GP handler for user space: an SGDT, SIDT or SMSW with a memory operand and a CS prefix leaves the task spinning in the kernel, never returning to user space, with a SIGKILL that is never delivered. Any user can thus tie up CPUs until reboot. With an FS or GS prefix, the emulated result is written to the wrong address. Rename the internal macro iterator variable. [ Lukas' original patch renamed the use site, I changed it to rename the iterator in the macro instead, but left Lukas' commit message and authorship - Linus ]
Severity
No CVSS data available.
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 6639 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 45e1dccc0653c50e377dae57ef086a8d0f71061d , < 0efe927053f7eabd1e8658cbda96ee3d78bd1765 (git)
Affected: 45e1dccc0653c50e377dae57ef086a8d0f71061d , < 32c52ec87d6245ee2d12ed5dd509e40062939b50 (git)
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Linux Linux Affected: 6.19
Unaffected: 0 , < 6.19 (semver)
Unaffected: 7.2.13 , ≤ 7.2.* (semver)
Unaffected: 7.3 , ≤ * (original_commit_for_fix)
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    "datePublished": "2026-10-28T10:35:44.049Z",
    "dateReserved": "2026-09-25T10:25:14.399Z",
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            "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\u0027 original patch renamed the use site, I changed it to rename the\n  iterator in the macro instead, but left Lukas\u0027 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",
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      "cve": "CVE-2026-99186",
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      "product_status:known_affected": "190",
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      "source": "Red Hat CSAF VEX",
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      "title": "kernel: kernel: Denial of Service via infinite loop in x86 instruction evaluation",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-99186.json",
      "version": "3"
    }
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}



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