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Windows Update CVE-2026-69999

| EUVDEUVD-2026-99855 MEDIUM
Out-of-bounds Read (CWE-125)
2026-10-13 secure@microsoft.com GHSA-wg7w-f2gw-73q6
5.5
CVSS 3.1 · Vendor: microsoft
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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

  1. Access
    Obtain low-privileged local session
  2. Exploit
    Invoke vulnerable Windows Update code path
  3. Execution
    Trigger out-of-bounds read (CWE-125)
  4. Impact
    Disclose adjacent process memory locally

Vulnerability Assessment

Weakness
CWE
ASVS 5.0
V15 - Secure Coding and Architecture Bounds checking, read limits
MITRE ATT&CK

1 technique across 1 tactic: Collection

The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up.

Exploitation Conditions

Exploitation requires the attacker to already have local, low-privileged authenticated access to the Windows host (CVSS PR:L, AV:L) and to reach the vulnerable Windows Update component; no user interaction is needed (UI:N). It cannot be triggered remotely or by an unauthenticated actor, which materially limits realistic risk. Impact is confined to information disclosure (C:H, I:N, A:N) - the flaw does not by itself grant code execution or privilege escalation. Affected builds are specific Windows 11 (23H2, 24H2, 25H2, 26H1, 26H2) and Windows Server 2025 versions below the patched build numbers listed in EUVD; hosts already updated past those build thresholds are not exposed.

Impact

This is a moderate, low-priority issue when all signals are weighed together. The CVSS 3.1 vector (AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N, base 5.5) describes a locally-exploitable, low-complexity flaw that requires existing low-level authenticated access and yields only a confidentiality impact (high C, no integrity or availability effect) - consistent with an out-of-bounds read (CWE-125) that discloses memory contents. CISA's SSVC decision framework reinforces the low urgency: Exploitation=none, Automatable=no, Technical Impact=partial. No EPSS score was provided in the input, the CVE is not listed in CISA KEV, and no public proof-of-concept is indicated, so there is no public exploit identified at time of analysis. The signals are mutually consistent rather than conflicting: a local-only, authenticated information-disclosure bug with no observed exploitation. The one thing to verify is that the 'partial' technical impact and C:H rating are reconciled - C:H implies significant data exposure, while SSVC 'partial' suggests constrained impact; this is a minor framing difference, not a contradiction. Overall: a genuine but lower-tier patch-cycle item, not an emergency, despite the ubiquity of the affected platform.

Exploit ScenarioDerived

An attacker who already has a low-privileged authenticated session on a Windows host (for example a standard local user or malware running in a normal user context) invokes the vulnerable Windows Update code path to trigger an out-of-bounds read, causing adjacent memory to be returned and disclosing sensitive data such as pointers or other process memory. No user interaction is required, but the attacker must first have local access and valid low-level privileges. No public exploit code is identified at time of analysis.

This Month Plan within 30 days. Why: MEDIUM severity (CVSS 4.0-6.9).
Patch available 0.4% exploitation probability (EPSS)

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AnalysisAIv1 – Oct 14, 2026

Information disclosure in the Microsoft Windows Update component allows a local, low-privileged authenticated attacker (CVSS AV:L/PR:L, UI:N) to trigger an out-of-bounds read and expose contents of process memory. Only specific Windows 11 builds (23H2, 24H2, 25H2, 26H1, 26H2) and Windows Server 2025 - including Server Core - below the fixed build numbers are affected; the flaw cannot be reached remotely or by an unauthenticated actor, and impact is limited to confidentiality (C:H) with no integrity or availability effect and no code execution or privilege escalation on its own. No public exploit code has been identified at time of analysis, CISA SSVC records exploitation as 'none', and vendor patches are available, making this a moderate, low-priority issue when all signals are weighed together.

RemediationAI

Vendor-released patch: install the Microsoft cumulative update that brings each affected build to or above the fixed build listed in the advisory - 10.0.22631.7652 for Windows 11 23H2, 10.0.26100.9711 for Windows 11 24H2, 10.0.26200.9711 for Windows 11 25H2, 10.0.28000.3231 for Windows 11 26H1, 10.0.26300.9711 for Windows 11 26H2, and 10.0.26100.33650 for Windows Server 2025 (including Server Core); patch details and applicability are in https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-69999. Because exploitation requires local interactive access with low privileges, the most effective compensating controls are least-privilege hardening and reducing who can log on locally to servers (restricting Remote Desktop, disabling shared local accounts), since no network or unauthenticated attack path exists and network segmentation or perimeter filtering would not mitigate this bug. Secondary controls include removing unnecessary local user rights and monitoring for anomalous reads or crashes in Windows Update processes, with the trade-off that these are detective rather than preventive and will not close the memory-safety defect; only the vendor update does. Prioritization can remain moderate given SSVC exploitation 'none', no identified public exploit, and the confidentiality-only, local-only impact profile.

Affected VersionsENISA

Windows Server 2025 (Server Core installation) 10.0.26100.0 <10.0.26100.33650
Windows 11 Version 26H2 10.0.26300.0 <10.0.26300.9711
Windows 11 Version 24H2 10.0.26100.0 <10.0.26100.9711
Windows 11 version 26H1 10.0.28000.0 <10.0.28000.3231
Windows 11 Version 25H2 10.0.26200.0 <10.0.26200.9711
Windows 11 Version 23H2 10.0.22631.0 <10.0.22631.7652
Windows Server 2025 10.0.26100.0 <10.0.26100.33650

Affected Packages

euvd windows_11_version_23h2 fix: 10.0.22631.7652
euvd windows_11_version_24h2 fix: 10.0.26100.9711
euvd windows_11_version_25h2 fix: 10.0.26200.9711
euvd windows_11_version_26h1 fix: 10.0.28000.3231
euvd windows_11_version_26h2 fix: 10.0.26300.9711
euvd windows_server_2025 fix: 10.0.26100.33650
euvd windows_server_2025_server_core_installation fix: 10.0.26100.33650

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 7 packages in euvd

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

The root cause class is CWE-125 (Out-of-bounds Read), and telemetry tags it as a buffer over-read class issue in the Windows Update service/component on the Windows platform. An out-of-bounds read occurs when code indexes past the end of an allocated buffer (heap or stack), causing adjacent memory to be interpreted as valid data and potentially returned or logged back to the caller; in a service context this can leak pointers, heap metadata, or incomplete memory structures that are useful for reconnaissance and, in a chained scenario, for defeating ASLR. The CVSS 3.1 vector CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N confirms the exposure is local (AV:L) and requires low-privileged authenticated access on the host (PR:L), with no user interaction (UI:N), scope unchanged (S:U), and a strictly confidential-impact profile (C:H, I:N, A:N). Because the vulnerable component is reached only from the local machine, there is no network-facing attack surface and no path to elevation of privilege or remote code execution through this defect by itself. The affected builds (per ENISA EUVD cross-reference for EUVD-2026-99855) share the Windows 10.0.22xxx/26xxx/28xxx kernel base, spanning Windows 11 23H2, 24H2, 25H2, 26H1 and 26H2 as well as Windows Server 2025 and its Server Core installation.

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  • Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

Vendor (microsoft) PRIMARY 5.5 MEDIUM
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
vuln.today AI 5.5 MEDIUM

Local authorized attacker (AV:L, PR:L) triggers an out-of-bounds read with low complexity and no user interaction; impact is confidentiality-only, so I:N and A:N.

3.1 AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
4.0 AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Primary rating from Vendor (microsoft).

CVSS VectorVendor: microsoft

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

Lifecycle Timeline

2
Patch available
Oct 13, 2026 - 20:20 EUVD
CVE Published
Oct 13, 2026 - 19:19 cve.org
MEDIUM 5.5

DescriptionCVE.org

Out-of-bounds read in Windows Update allows an authorized attacker to disclose information locally.

Threat Intelligence Overview

EPSS Score
0.4%
Top 66% exploitable
Prevalence
Ubiquitous
Windows 11 and Windows Server 2025 run in a huge fraction of environments
Vendor Status
Publicly Disclosed:No
Exploited:No
Latest Software Release:Exploitation Less Likely
Data Quality
4 sources
Confidence: Medium

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity MEDIUM
CISA KEV No
Public POC No
EPSS 0.4%
Patch available Yes
Active threat No
Deciding rule
MEDIUM severity (CVSS 4.0-6.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Defer
Exploitation
None
System Exposure· derived
Small
Automatable
No
Human Impact· derived
Medium
Technical Impact
Partial

Priority Score

28
Low Medium High Critical
KEV: 0
EPSS: 0
CVSS: +28
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

A buffer overflow occurs when a program writes more data to a memory buffer than it was allocated to hold, causing the excess data to spill into adjacent memory regions.

Information disclosure occurs when an application unintentionally exposes sensitive data that aids attackers in reconnaissance or directly compromises security.

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