VulnerabilityPublished 28 Oct 2026

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

Source GCVE Database

Authoritative record:CVE-2026-99186

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

Data as of 28 Oct 2026, 13:46 UTC

Severity

High

Rated High by Threat Radar's AI analysis · 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.

ghsa-252w-9m2h-vq2g

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.

AI-suggested

A code fix has been implemented to rename the internal macro iterator variable, resolving the variable shadowing issue and correcting segment prefix handling. Users should apply the official Linux kernel patch that includes this fix to prevent CPU hangs and incorrect memory writes caused by this vulnerability.

Description

A vulnerability in the Linux kernel's x86 instruction evaluation code caused incorrect handling of segment register overrides. This flaw led to infinite loops or incorrect memory writes during UMIP emulation triggered by certain instructions with segment prefixes. An unprivileged user could exploit this to cause CPU hangs, tying up system resources until reboot.

Impact

An unprivileged user can cause the kernel to enter an infinite loop during UMIP emulation of certain instructions, tying up CPU resources indefinitely until a reboot. Additionally, FS or GS prefix handling could cause incorrect memory writes. This results in a denial of service condition affecting system availability.

Summary

The vulnerability arises from a variable shadowing issue in the function get_seg_reg_override_idx() within the Linux kernel's x86 instruction evaluation code. A loop counter variable named 'idx' was shadowed by a local variable of the same name, causing the function to always return a default segment register value and ignore FS and GS overrides. Additionally, a CS override caused an infinite loop in the prefix processing, leading to the kernel spinning indefinitely in the #GP handler during UMIP emulation triggered by SGDT, SIDT, or SMSW instructions with a CS prefix. This results in CPU resource exhaustion and a SIGKILL that is never delivered, effectively causing a denial of service. The fix involved renaming the internal macro iterator variable to eliminate the shadowing.

References

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