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Windows Event Log CVE-2026-83695

| EUVDEUVD-2026-99954 MEDIUM
Use of Uninitialized Resource (CWE-908)
2026-10-13 secure@microsoft.com GHSA-r53r-mmx7-483q
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-priv local session
  2. Exploit
    Invoke Event Logging Service API
  3. Execution
    Trigger read of uninitialized resource
  4. Impact
    Harvest leaked sensitive memory contents

Vulnerability Assessment

Weakness
CWE
ASVS 5.0
V15 - Secure Coding and Architecture Variable initialization
Exploitation Conditions

Requires the attacker to already have local, authenticated code execution on the target Windows host at low privilege (PR:L) - there is no remote or unauthenticated path (AV:L rules out network delivery, UI:N means no victim interaction is needed once local). The weakness (CWE-908, use of uninitialized resource) is exercised by locally invoking the Windows Event Logging Service, which can expose stale memory contents. Limiting factors: the attacker must first establish a foothold and a valid local session, exploitation is not automatable per SSVC, and impact is confined to information disclosure (I:N/A:N) on the affected build ranges prior to the patched versions listed in the EUVD advisory; patched builds eliminate the condition.

Impact

This is a moderate-severity local information disclosure flaw (CVSS 5.5) whose signals are consistent and point to LOW real-world urgency despite the HIGH confidentiality impact. The CVSS vector (AV:L/AC:L/PR:L/UI:N) requires local access and at least low-level authentication, so this is not remotely exploitable and cannot be triggered by an anonymous network attacker. CISA's SSVC framework reinforces this: Exploitation=none (no observed or public exploitation), Automatable=no (cannot be reliably mass-exploited/wormed), and Technical Impact=partial. The flaw is NOT in CISA KEV and no POC is referenced in the provided intelligence, so there is no evidence of active or imminent exploitation. The only tension worth noting is between the C:H rating and the SSVC 'partial' technical impact: CVSS treats the leaked data as highly confidential, while SSVC judges the overall control gained as partial - this is a leak of sensitive memory/log contents rather than full compromise. Net: a legitimate patch-management item that fits a normal Patch-Tuesday cycle, not an emergency. It is realistically useful to an attacker only as a secondary step (e.g., post-foothold privilege-escalation reconnaissance), not as an initial-access vector.

Exploit ScenarioDerived

An attacker who already has a low-privileged authenticated session on a Windows host (e.g., via phishing, stolen credentials, or a compromised service account) runs a crafted local process that interacts with the Event Logging Service and reads back uninitialized memory contents, disclosing sensitive data such as credentials, tokens, or pointers that were never cleared. No public exploit code is identified at time of analysis, and the attack requires local access plus valid privileges, so it serves as a post-compromise information-gathering step rather than a standalone remote break-in.

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 via use of an uninitialized resource in the Microsoft Windows Event Logging Service allows a locally authenticated attacker holding only low privileges (PR:L) to read stale memory contents from the affected service, yielding high confidentiality impact with no integrity or availability effect (CVSS 5.5, CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N). Only hosts running unpatched builds of Windows 10, Windows 11, and Windows Server 2012 through 2025 within the version ranges listed in the EUVD advisory are affected, and the flaw cannot be reached remotely - an attacker must already have local code execution and a valid session on the target. Exploitation is not automatable per SSVC (Exploitation: none, Automatable: no, Technical Impact: partial), and no public exploit is identified at time of analysis, so real-world urgency is LOW despite the HIGH confidentiality rating; vendor patches are available that eliminate the condition.

RemediationAI

Apply the Microsoft vendor-released patch, which fixes the issue by properly initializing the affected resource; the fixed builds per the EUVD advisory are Windows 10 1607 10.0.14393.9612, Windows 10 1809 / Server 2019 10.0.17763.9376, Windows 10 21H2 10.0.19044.7807, Windows 10 22H2 10.0.19045.7807, Windows 11 23H2 10.0.22631.7652, Windows 11 24H2 10.0.26100.9711, Windows 11 25H2 10.0.26200.9711, Windows 11 26H1 10.0.28000.3231, Windows 11 26H2 10.0.26300.9711, Server 2012 6.2.9200.26434, Server 2012 R2 6.3.9600.23470, Server 2016 10.0.14393.9612, Server 2022 10.0.20348.5761, and Server 2025 10.0.26100.33650; install the corresponding cumulative update from https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-83695 and verify the reported OS build against these thresholds. Because the attack requires the adversary to already hold low-privileged local code execution (AV:L/PR:L), the most effective compensating controls are ones that deny that foothold: enforce least privilege and remove unnecessary local interactive and service accounts, restrict who can log on locally via 'Allow log on locally' and 'Deny log on locally' policy, and apply application control (WDAC/AppLocker) plus EDR behavioral detection so untrusted binaries cannot invoke the Event Logging service to harvest memory. Where a host cannot be patched, its exposure only materializes after local compromise, so network segmentation, privileged-access workstations, and rapid credential rotation for any host known to be compromised reduce the value of the disclosed data; disabling the Windows Event Log service outright is not a viable workaround because it removes the audit telemetry security teams rely on for detection and violates baseline logging requirements, and aggressive memory-hardening tweaks (for example forcing heap zeroing) carry performance and application-compatibility side effects and do not address the specific uninitialized path. Given SSVC reports Exploitation: none, Automatable: no, no public exploit is identified at time of analysis, so remediation should be scheduled through normal monthly patch cycles rather than emergency change.

Affected VersionsENISA

Windows 10 Version 21H2 10.0.19044.0 <10.0.19044.7807
Windows Server 2019 10.0.17763.0 <10.0.17763.9376
Windows 11 Version 24H2 10.0.26100.0 <10.0.26100.9711
Windows Server 2012 R2 6.3.9600.0 <6.3.9600.23470
Windows Server 2016 10.0.14393.0 <10.0.14393.9612
Windows Server 2012 (Server Core installation) 6.2.9200.0 <6.2.9200.26434
Windows Server 2016 (Server Core installation) 10.0.14393.0 <10.0.14393.9612
Windows 11 version 26H1 10.0.28000.0 <10.0.28000.3231
Windows Server 2025 (Server Core installation) 10.0.26100.0 <10.0.26100.33650
Windows 11 Version 23H2 10.0.22631.0 <10.0.22631.7652
Windows Server 2012 R2 (Server Core installation) 6.3.9600.0 <6.3.9600.23470
Windows Server 2025 10.0.26100.0 <10.0.26100.33650
Windows 11 Version 26H2 10.0.26300.0 <10.0.26300.9711
Windows 10 Version 22H2 10.0.19045.0 <10.0.19044.7807
Windows 11 Version 25H2 10.0.26200.0 <10.0.26200.9711
Windows Server 2022 10.0.20348.0 <10.0.20348.5761
Windows 10 Version 1809 10.0.17763.0 <10.0.17763.9376
Windows 10 Version 1607 10.0.14393.0 <10.0.14393.9612
Windows Server 2012 6.2.9200.0 <6.2.9200.26434
Windows Server 2019 (Server Core installation) 10.0.17763.0 <10.0.17763.9376

Affected Packages

euvd windows_10_version_1607 fix: 10.0.14393.9612
euvd windows_10_version_1809 fix: 10.0.17763.9376
euvd windows_10_version_21h2 fix: 10.0.19044.7807
euvd windows_10_version_22h2 fix: 10.0.19044.7807
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_2012 fix: 6.2.9200.26434
euvd windows_server_2012_r2 fix: 6.3.9600.23470
euvd windows_server_2012_r2_server_core_installation fix: 6.3.9600.23470
euvd windows_server_2012_server_core_installation fix: 6.2.9200.26434
euvd windows_server_2016 fix: 10.0.14393.9612
euvd windows_server_2016_server_core_installation fix: 10.0.14393.9612
euvd windows_server_2019 fix: 10.0.17763.9376
euvd windows_server_2019_server_core_installation fix: 10.0.17763.9376
euvd windows_server_2022 fix: 10.0.20348.5761
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 20 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 vulnerability is rooted in CWE-908, Use of Uninitialized Resource, inside the Windows Event Logging Service (the EventLog/Wevtapi component that writes, stores, and serves Windows event records). When a resource - most plausibly a heap or stack buffer used while formatting, serializing, or retrieving event data - is allocated but not fully initialized before being read, residual memory from prior operations can be returned to the caller instead of initialized data. Because the service runs with elevated privileges and handles data from many other system and application components, that uninitialized region can contain sensitive material belonging to other processes or the kernel, which is why the confidentiality impact is rated High (C:H) while integrity and availability are None. The attack is strictly local (AV:L) with low privileges required (PR:L) and no user interaction (UI:N), meaning the weakness is exercised by locally invoking the service after obtaining a foothold on the host; there is no network or unauthenticated delivery path, and per SSVC the flaw is not automatable, so it is a chained post-compromise primitive rather than a standalone intrusion vector. Affected CPE/build ranges span Windows 10 (1607, 1809, 21H2, 22H2), Windows 11 (23H2, 24H2, 25H2, 26H1, 26H2), and Windows Server 2012, 2012 R2, 2016, 2019, 2022, and 2025, including their Server Core installation variants.

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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-only service interaction requires an authenticated low-priv session (AV:L, PR:L), triggering is reliable (AC:L), and the flaw leaks sensitive data with no integrity or availability effect (C:H, I:N, 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 - 19:20 cve.org
MEDIUM 5.5

DescriptionCVE.org

Use of uninitialized resource in Windows Event Logging Service allows an authorized attacker to disclose information locally.

Threat Intelligence Overview

EPSS Score
0.4%
Top 66% exploitable
Prevalence
Ubiquitous
Core Windows OS component present across nearly all client/server Windows deployments
Vendor Status
Publicly Disclosed:No
Exploited:No
Latest Software Release:Exploitation Less Likely
Data Quality
5 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

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