VulnerabilityPublished 28 Oct 2026

CVE-2026-99186: Linux kernel · x86/insn-eval: Fix shadowed segment index in get_seg_reg_override_idx()

Affects Linux kernelSource CVE Database V5

Not known to be exploited : upgrade to 32c52ec87d6245ee2d12ed5dd509e40062939b50 or 0efe927053f7eabd1e8658cbda96ee3d78bd1765 when convenient.

Data as of 28 Oct 2026, 10:58 UTC

Severity

Unrated

Rated by Threat Radar · CVSS not yet scored by NVD

Patch: Available – fixed in 32c52ec87d6245ee2d12ed5dd509e40062939b50, 0efe927053f7eabd1e8658cbda96ee3d78bd1765

Exploitation evidence

Disclosed: evidence found.
CVE published 28 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade Linux kernel to 32c52ec87d6245ee2d12ed5dd509e40062939b50 or 0efe927053f7eabd1e8658cbda96ee3d78bd1765.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ 45e1dccc0653c50e377dae57ef086a8d0f71061d, < 32c52ec87d6245ee2d12ed5dd509e40062939b50	Fixed in 32c52ec87d6245ee2d12ed5dd509e40062939b50
LinuxLinux	Affected ≥ 45e1dccc0653c50e377dae57ef086a8d0f71061d, < 0efe927053f7eabd1e8658cbda96ee3d78bd1765	Fixed in 0efe927053f7eabd1e8658cbda96ee3d78bd1765
LinuxLinux	Affected =6.19	Fixed in–
Debiandebian/linux`pkg:deb/debian/linux`Other threats	Affected =6.19	Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

Description

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 ]

References

Community reviews

Loading reviews…