ADV180022 — Windows Denial of Service Vulnerability

Executive Summary

Microsoft is aware of a denial of service vulnerability (named "FragmentSmack" CVE-2018-5391) affecting Windows systems. An attacker could send many 8-byte sized IP fragments with random starting offsets, but withhold the last fragment and exploit the worst-case complexity of linked lists in reassembling IP fragments. A system under attack would become unresponsive with 100% CPU utilization but would recover as soon as the attack terminated. To protect your system from this vulnerability, Microsoft recommends that you take the following actions: 1. What workaround(s) exist for this vulnerability? The following commands disable packet reassembly. Any out-of-order packets are dropped. There is a potential for packet loss when discarding out-of-order packets. Valid scenarios should not exceed more than 50 out-of-order fragments. We recommend testing prior to updating production systems. Further netsh guidance can be found at netsh . 2. Is Azure affected? Azure fabric layer protections mitigate this vulnerability. This is blocked before traffic reaches Azure VMs. 3. What can I do at the perimeter to block this attack? Review the perimeter device guidance and modify reassembly packet limits similar to the commands listed in FAQ #1 .

Overview

Important

MS Severity

Not Exploited

MS Exploit Status

Less Likely

MS Exploit Likelihood

Category Denial of Service

Released Sep 11 2018

Last Updated Sep 11 2018

Publicly Disclosed No

CISA KEV Not Listed

Known Exploits None Known

EPSS Score

No EPSS score available for this CVE.

View on FIRST.org

Affected Products

15 affected products

Product	KB Article	Severity	Impact	Restart Required
Windows 10 for 32-bit Systems	`4457132 (Security Update)`	Important	Denial of Service	Yes
Windows 10 for x64-based Systems	`4457132 (Security Update)`	Important	Denial of Service	Yes
Windows 10 Version 1607 for 32-bit Systems	`4457131 (Security Update)`	Important	Denial of Service	Yes
Windows 10 Version 1607 for x64-based Systems	`4457131 (Security Update)`	Important	Denial of Service	Yes
Windows 10 Version 1703 for 32-bit Systems	`4457138 (Security Update)`	Important	Denial of Service	Yes
Windows 10 Version 1703 for x64-based Systems	`4457138 (Security Update)`	Important	Denial of Service	Yes
Windows 10 Version 1709 for 32-bit Systems	`4457142 (Security Update)`	Important	Denial of Service	Yes
Windows 10 Version 1709 for x64-based Systems	`4457142 (Security Update)`	Important	Denial of Service	Yes
Windows 10 Version 1803 for 32-bit Systems	`4457128 (Security Update)`	Important	Denial of Service	Yes
Windows 10 Version 1803 for x64-based Systems	`4457128 (Security Update)`	Important	Denial of Service	Yes
Windows 7 for 32-bit Systems Service Pack 1 4457144 (Monthly Rollup) 4457145 (Security Only) Important Denial of Service 4343900 Base: N/A Temporal: N/A Vector: N/A Yes None Windows 7 for x64-based Systems Service Pack 1 4457144 (Monthly Rollup) 4457145 (Security Only) Important Denial of Service 4343900 Base: N/A Temporal: N/A Vector: N/A Yes None Windows 8.1 for 32-bit systems 4457129 (Monthly Rollup) 4457143 (Security Only) Important Denial of Service 4343898 Base: N/A Temporal: N/A Vector: N/A Yes None Windows 8.1 for x64-based systems 4457129 (Monthly Rollup) 4457143 (Security Only) Important Denial of Service 4343898 Base: N/A Temporal: N/A Vector: N/A Yes None Windows RT 8.1	`4457129 (Monthly Rollup)`	Important	Denial of Service	Yes
Windows Server 2008 for 32-bit Systems Service Pack 2 4458010 (Monthly Rollup) 4457984 (Security Only) Important Denial of Service Base: N/A Temporal: N/A Vector: N/A Yes None Windows Server 2008 for 32-bit Systems Service Pack 2 (Server Core installation) 4458010 (Monthly Rollup) 4457984 (Security Only) Important Denial of Service Base: N/A Temporal: N/A Vector: N/A Yes None Windows Server 2008 for Itanium-Based Systems Service Pack 2 4458010 (Monthly Rollup) 4457984 (Security Only) Important Denial of Service Base: N/A Temporal: N/A Vector: N/A Yes None Windows Server 2008 for x64-based Systems Service Pack 2 4458010 (Monthly Rollup) 4457984 (Security Only) Important Denial of Service Base: N/A Temporal: N/A Vector: N/A Yes None Windows Server 2008 for x64-based Systems Service Pack 2 (Server Core installation) 4458010 (Monthly Rollup) 4457984 (Security Only) Important Denial of Service Base: N/A Temporal: N/A Vector: N/A Yes None Windows Server 2008 R2 for Itanium-Based Systems Service Pack 1 4457144 (Monthly Rollup) 4457145 (Security Only) Important Denial of Service 4343900 Base: N/A Temporal: N/A Vector: N/A Yes None Windows Server 2008 R2 for x64-based Systems Service Pack 1 4457144 (Monthly Rollup) 4457145 (Security Only) Important Denial of Service 4343900 Base: N/A Temporal: N/A Vector: N/A Yes None Windows Server 2008 R2 for x64-based Systems Service Pack 1 (Server Core installation) 4457144 (Monthly Rollup) 4457145 (Security Only) Important Denial of Service 4343900 Base: N/A Temporal: N/A Vector: N/A Yes None Windows Server 2012 4457135 (Monthly Rollup) 4457140 (Security Only) Important Denial of Service 4343901 Base: N/A Temporal: N/A Vector: N/A Yes None Windows Server 2012 (Server Core installation) 4457135 (Monthly Rollup) 4457140 (Security Only) Important Denial of Service 4343901 Base: N/A Temporal: N/A Vector: N/A Yes None Windows Server 2012 R2 4457129 (Monthly Rollup) 4457143 (Security Only) Important Denial of Service 4343898 Base: N/A Temporal: N/A Vector: N/A Yes None Windows Server 2012 R2 (Server Core installation) 4457129 (Monthly Rollup) 4457143 (Security Only) Important Denial of Service 4343898 Base: N/A Temporal: N/A Vector: N/A Yes None Windows Server 2016	`4457131 (Security Update)`	Important	Denial of Service	Yes
Windows Server 2016 (Server Core installation)	`4457131 (Security Update)`	Important	Denial of Service	Yes
Windows Server, version 1709 (Server Core Installation)	`4457142 (Security Update)`	Important	Denial of Service	Yes
Windows Server, version 1803 (Server Core Installation)	`4457128 (Security Update)`	Important	Denial of Service	Yes

Patches

6 patches

Article	Type	Restart
`4457132`	Security Update	Yes
`4457131`	Security Update	Yes
`4457138`	Security Update	Yes
`4457142`	Security Update	Yes
`4457128`	Security Update	Yes
`4457129`	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

Juha-Matti Tilli of Aalto University Department of Communications and Networking

References

MSRC Advisory MITRE NVD