Windows NTLM
CVE-2019-1166 — Windows NTLM Tampering Vulnerability
Executive Summary
A tampering vulnerability exists in Microsoft Windows when a man-in-the-middle attacker is able to successfully bypass the NTLM MIC (Message Integrity Check) protection. An attacker who successfully exploited this vulnerability could gain the ability to downgrade NTLM security features. To exploit this vulnerability, the attacker would need to tamper with the NTLM exchange. The attacker could then modify flags of the NTLM packet without invalidating the signature. The update addresses the vulnerability by hardening NTLM MIC protection on the server-side.
Overview
5.9
CVSS MEDIUM
Important
MS Severity
Not Exploited
MS Exploit Status
Less Likely
MS Exploit Likelihood
CVSS Vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N/E:P/RL:O/RC:C
ATTACK VECTOR
Network
ATTACK COMPLEXITY
High
PRIVILEGES REQUIRED
None
USER INTERACTION
None
SCOPE
Unchanged
CONFIDENTIALITY
None
INTEGRITY
High
AVAILABILITY
None
EXPLOIT CODE MATURITY
Proof-of-Concept
REMEDIATION LEVEL
Official Fix
REPORT CONFIDENCE
Confirmed
Temporal Score: 5.3
EPSS Score
0.61676
probability of exploitation in the next 30 days
0.99084 percentile - updated 2026-07-25
View on FIRST.org
Affected Products
25 affected products
| Product | KB Article | Severity | Impact | Restart Required |
|---|---|---|---|---|
| Windows 10 for 32-bit Systems | 4520011 (Security Update) |
Important | Tampering | Yes |
| Windows 10 for x64-based Systems | 4520011 (Security Update) |
Important | Tampering | Yes |
| Windows 10 Version 1607 for 32-bit Systems | 4519998 (Security Update) |
Important | Tampering | Yes |
| Windows 10 Version 1607 for x64-based Systems | 4519998 (Security Update) |
Important | Tampering | Yes |
| Windows 10 Version 1703 for 32-bit Systems | 4520010 (Security Update) |
Important | Tampering | Yes |
| Windows 10 Version 1703 for x64-based Systems | 4520010 (Security Update) |
Important | Tampering | Yes |
| Windows 10 Version 1709 for 32-bit Systems | 4520004 (Security Update) |
Important | Tampering | Yes |
| Windows 10 Version 1709 for ARM64-based Systems | 4520004 (Security Update) |
Important | Tampering | Yes |
| Windows 10 Version 1709 for x64-based Systems | 4520004 (Security Update) |
Important | Tampering | Yes |
| Windows 10 Version 1803 for 32-bit Systems | 4520008 (Security Update) |
Important | Tampering | Yes |
| Windows 10 Version 1803 for ARM64-based Systems | 4520008 (Security Update) |
Important | Tampering | Yes |
| Windows 10 Version 1803 for x64-based Systems | 4520008 (Security Update) |
Important | Tampering | Yes |
| Windows 10 Version 1809 for 32-bit Systems | 4519338 (Security Update) |
Important | Tampering | Yes |
| Windows 10 Version 1809 for ARM64-based Systems | 4519338 (Security Update) |
Important | Tampering | Yes |
| Windows 10 Version 1809 for x64-based Systems | 4519338 (Security Update) |
Important | Tampering | Yes |
| Windows 10 Version 1903 for 32-bit Systems | 4517389 (Security Update) |
Important | Tampering | Yes |
| Windows 10 Version 1903 for ARM64-based Systems | 4517389 (Security Update) |
Important | Tampering | Yes |
| Windows 10 Version 1903 for x64-based Systems | 4517389 (Security Update) |
Important | Tampering | Yes |
| Windows 7 for 32-bit Systems Service Pack 1 4519976 (Monthly Rollup) 4520003 (Security Only) Important Tampering 4524157 Base: 5.9 Temporal: 5.3 Vector: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N/E:P/RL:O/RC:C Yes None Windows 7 for x64-based Systems Service Pack 1 4519976 (Monthly Rollup) 4520003 (Security Only) Important Tampering 4524157 Base: 5.9 Temporal: 5.3 Vector: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N/E:P/RL:O/RC:C Yes None Windows 8.1 for 32-bit systems 4520005 (Monthly Rollup) 4519990 (Security Only) Important Tampering 4524156 Base: 5.9 Temporal: 5.3 Vector: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N/E:P/RL:O/RC:C Yes None Windows 8.1 for x64-based systems 4520005 (Monthly Rollup) 4519990 (Security Only) Important Tampering 4524156 Base: 5.9 Temporal: 5.3 Vector: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N/E:P/RL:O/RC:C Yes None Windows RT 8.1 | 4520005 (Monthly Rollup) |
Important | Tampering | Yes |
| Windows Server 2008 for 32-bit Systems Service Pack 2 4520002 (Monthly Rollup) 4520009 (Security Only) Important Tampering 4516026 Base: 5.9 Temporal: 5.3 Vector: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N/E:P/RL:O/RC:C Yes None Windows Server 2008 for 32-bit Systems Service Pack 2 (Server Core installation) 4520002 (Monthly Rollup) 4520009 (Security Only) Important Tampering 4516026 Base: 5.9 Temporal: 5.3 Vector: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N/E:P/RL:O/RC:C Yes None Windows Server 2008 for Itanium-Based Systems Service Pack 2 4520002 (Monthly Rollup) 4520009 (Security Only) Important Tampering 4516026 Base: 5.9 Temporal: 5.3 Vector: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N/E:P/RL:O/RC:C Yes None Windows Server 2008 for x64-based Systems Service Pack 2 4520002 (Monthly Rollup) 4520009 (Security Only) Important Tampering 4516026 Base: 5.9 Temporal: 5.3 Vector: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N/E:P/RL:O/RC:C Yes None Windows Server 2008 for x64-based Systems Service Pack 2 (Server Core installation) 4520002 (Monthly Rollup) 4520009 (Security Only) Important Tampering 4516026 Base: 5.9 Temporal: 5.3 Vector: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N/E:P/RL:O/RC:C Yes None Windows Server 2008 R2 for Itanium-Based Systems Service Pack 1 4519976 (Monthly Rollup) 4520003 (Security Only) Important Tampering 4524157 Base: 5.9 Temporal: 5.3 Vector: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N/E:P/RL:O/RC:C Yes None Windows Server 2008 R2 for x64-based Systems Service Pack 1 4519976 (Monthly Rollup) 4520003 (Security Only) Important Tampering 4524157 Base: 5.9 Temporal: 5.3 Vector: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N/E:P/RL:O/RC:C Yes None Windows Server 2008 R2 for x64-based Systems Service Pack 1 (Server Core installation) 4519976 (Monthly Rollup) 4520003 (Security Only) Important Tampering 4524157 Base: 5.9 Temporal: 5.3 Vector: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N/E:P/RL:O/RC:C Yes None Windows Server 2012 4520007 (Monthly Rollup) 4519985 (Security Only) Important Tampering 4524154 Base: 5.9 Temporal: 5.3 Vector: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N/E:P/RL:O/RC:C Yes None Windows Server 2012 (Server Core installation) 4520007 (Monthly Rollup) 4519985 (Security Only) Important Tampering 4524154 Base: 5.9 Temporal: 5.3 Vector: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N/E:P/RL:O/RC:C Yes None Windows Server 2012 R2 4520005 (Monthly Rollup) 4519990 (Security Only) Important Tampering 4524156 Base: 5.9 Temporal: 5.3 Vector: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N/E:P/RL:O/RC:C Yes None Windows Server 2012 R2 (Server Core installation) 4520005 (Monthly Rollup) 4519990 (Security Only) Important Tampering 4524156 Base: 5.9 Temporal: 5.3 Vector: CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N/E:P/RL:O/RC:C Yes None Windows Server 2016 | 4519998 (Security Update) |
Important | Tampering | Yes |
| Windows Server 2016 (Server Core installation) | 4519998 (Security Update) |
Important | Tampering | Yes |
| Windows Server 2019 | 4519338 (Security Update) |
Important | Tampering | Yes |
| Windows Server 2019 (Server Core installation) | 4519338 (Security Update) |
Important | Tampering | Yes |
| Windows Server, version 1803 (Server Core Installation) | 4520008 (Security Update) |
Important | Tampering | Yes |
| Windows Server, version 1903 (Server Core installation) | 4517389 (Security Update) |
Important | Tampering | Yes |
Patches
8 patches
| Article | Type | Restart |
|---|---|---|
4520011 |
Security Update | Yes |
4519998 |
Security Update | Yes |
4520010 |
Security Update | Yes |
4520004 |
Security Update | Yes |
4520008 |
Security Update | Yes |
4519338 |
Security Update | Yes |
4517389 |
Security Update | Yes |
4520005 |
Monthly Rollup | Yes |
Known Exploits
No known exploits have been linked for this CVE yet. When available, exploit references will be sourced from public repositories and may be unverified, incomplete, or non-functional. Always review code carefully before use in any environment.
Acknowledgments
Yaron Zinar from Preempt
References
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