Threats / Microsoft / CVE-2020-1040
CVE-2020-1040
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-08-04
Microsoft Hyper-V RemoteFX vulnerability
Microsoft Hyper-V RemoteFX vGPU fails to validate input from authenticated guest users, enabling remote code execution on the host operating system.
Verdict
Today item — known-exploited.
An authenticated attacker with guest OS access can exploit improper input validation in RemoteFX vGPU to execute arbitrary code on the Hyper-V host, compromising the entire virtualization infrastructure and all hosted guests.
CISA KEV Yes · 2021-11-034EPSS 0.06903 (verify live)5CVSS 9 (CISA)3CISA SSVC Exploitation: active · Automatable: no · Impact: total3
01
Is it exploitable?
— the evidence, ranked above the scoreReported exploitation
3 independent public reports of in-the-wild exploitation are cataloged.Distinct reporting sources (vendor, incident response, government); open them for the underlying claims.
Exploited in the wild
Listed in the CISA Known Exploited Vulnerabilities catalog (added 2021-11-03).
Probability (EPSS)
EPSS 0.06903 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
CVSS 9 (CVSS:3.1/AV:A/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H) · Affected: Microsoft, Hyper-V RemoteFX. Confirm exact fixed builds in the vendor advisory.CVSS — CISA-assigned via the ADP container (CVE.org), version 3.1; the CNA left no metrics, so CISA's own score is used ahead of NVD.
Weakness (CWE)
Mapped to CWE-20 Improper Input Validation.CWE assignment from the public NVD record (may be stale); the weakness class drives how the flaw is exploited.
CISA SSVC (triage disposition)
Exploitation: active · Automatable: no · Technical Impact: totalCISA's own stakeholder-specific triage inputs, published in the CVE record (CISA Coordinator role). NOTE: this is CISA's three decision points; the final Act/Attend/Track decision also requires a Mission & Well-being input not published here, so no overall decision is asserted.
Currency of the record
CISA added this to its KEV catalog 477 days after the CVE record was published.KEV lag = CISA-KEV dateAdded − CVE.org datePublished; a floor on how long the known-exploited flaw sat in the public record before the federal catalog listed it. Severity/weakness here is CNA- or CISA-assigned (current at disclosure), independent of NVD's analysis backlog.
02
Who’s exploiting it?
— attribution turns risk into urgencyAttribution not established
No confirmed (advisory-backed) threat-actor attribution is established for this record. Absence of a named actor is not absence of compromise — see Coverage & confidence.
03
Why it matters
— the attack path, told twice: adversary, then board1
Front door — unauthenticated access narrative 1
Attacker
I authenticate to a guest virtual machine and send specially crafted input to the RemoteFX vGPU interface.
Business
Guest isolation is bypassed, exposing the hypervisor to direct attack from tenant workloads.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I exploit the input validation flaw to execute arbitrary code with host-level privileges.
Business
The Hyper-V host is compromised, enabling lateral movement to all virtual machines and underlying infrastructure.
3
Lateral reach — past segmentation narrative 3
Attacker
I establish persistent control over the virtualization platform and its hosted environment.
Business
Multi-tenant environments face complete infrastructure compromise, data exfiltration, and service disruption across all hosted systems.
04
What to do
— defensible action- Remediate per the vendor advisory — confirm the fixed build for your version and verify exposure.1
Say it to the boardA vulnerability with this evidence profile is a defensible budget line, not a backlog ticket — fund the change against the proof above.
05