BCY-ADV-2026-006 MEDIUM 5.6

Spectre & Meltdown — CPU Speculative Execution
CVE-2017-5715 / CVE-2017-5754 · Hardware-Level · OS & Microcode Mitigations Required

CVE-2017-5715CVE-2017-5754SpectreMeltdownCPUSide-ChannelHardware
Prepared by Warren Barr · Barr Cyber LLC · barr-cyber.com · May 2026
What This Is
Hardware-level speculative execution vulnerabilities affecting virtually all modern CPUs. Spectre and Meltdown allow attackers to read memory that should be inaccessible — including kernel memory, other process memory, and in virtualized environments, other VM memory on the same physical host. Cannot be fully patched at the hardware level — mitigations are applied at OS and firmware level at a performance cost.
CVE Details
CVE-2017-5715 — Spectre Variant 2 (Branch Target Injection) — CVSS 5.6
CVE-2017-5753 — Spectre Variant 1 (Bounds Check Bypass) — CVSS 5.6
CVE-2017-5754 — Meltdown (Rogue Data Cache Load) — CVSS 5.6
Affected: Intel, AMD, ARM — virtually all hardware since ~1995
Mitigations: Windows Update (OS patches) + BIOS/UEFI update (microcode)
How It Works
Modern CPUs execute instructions speculatively — predicting code paths and running ahead. When the prediction is wrong, the work is discarded, but traces remain in the CPU cache. Spectre and Meltdown measure these cache traces via timing side-channels to infer the value of memory that should not be accessible. JavaScript-based Spectre exploits have been demonstrated running in browsers. On shared cloud infrastructure, cross-VM memory reads have been demonstrated in proof-of-concept research.
Detection — Verify Mitigations Active
Check via SpeculationControl module (PowerShell — administrator):
Install-Module SpeculationControl -Force -Scope CurrentUser Import-Module SpeculationControl Get-SpeculationControlSettings
# All key flags should show True: BTIWindowsSupportEnabled : True KVAShadowWindowsSupportEnabled : True BTIDisabledBySystemPolicy : False BTIDisabledByNoHardwareSupport : False
IOCs
Type Hardware side-channel — no traditional malware IOC Attack Surface Any code executing on CPU including browser JavaScript Timing Tool RDTSC / RDTSCP instructions for cache timing measurement Risk Shared physical hosts — cloud VMs, Hyper-V, VMware Detection SpeculationControl module — Get-SpeculationControlSettings Browser Disable high-precision timers (browser setting) reduces JS attack surface
Mitigation — PowerShell Commands

Step 1 — Verify and install OS patches:

Get-HotFix | Sort-Object InstalledOn -Descending | Select-Object -First 10

Step 2 — Update CPU microcode via BIOS/UEFI: Check your hardware manufacturer's site for the latest BIOS update. OS patches alone are insufficient without updated microcode.

Step 3 — Verify all mitigations active:

Install-Module SpeculationControl -Force -Scope CurrentUser Get-SpeculationControlSettings

Step 4 — Enable mitigations explicitly if SpeculationControl shows gaps:

reg add "HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management" /v FeatureSettingsOverride /t REG_DWORD /d 72 /f reg add "HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management" /v FeatureSettingsOverrideMask /t REG_DWORD /d 3 /f

Sources
— NVD — CVE-2017-5715 (Spectre)
— NVD — CVE-2017-5754 (Meltdown)
— Microsoft KB4073119 — Windows Guidance
BCY-ADV-2026-006 · Published May 2026 · Barr Cyber LLC · Kalispell, MT
Questions? warren@barr-cyber.com
Barr Cyber — Endpoint Hardening & System Configuration

Spectre and Meltdown mitigation verification is part of every Barr Cyber endpoint hardening sequence. Barr Cyber uses the SpeculationControl PowerShell module to confirm all flags are active post-reboot.

Get in Touch →
← WPAD Proxy Hijack All Advisories Next — LLMNR Poisoning →