CVE-2020-1301: Microsoft Windows 10 SMBv1 RCE Vulnerability

CVE-2020-1301 Overview

A remote code execution vulnerability exists in the way that the Microsoft Server Message Block 1.0 (SMBv1) server handles certain requests. This vulnerability, known as the 'Windows SMB Remote Code Execution Vulnerability', allows an authenticated attacker to execute arbitrary code on a target server by sending a specially crafted request to the SMBv1 server.

Critical Impact

Successful exploitation allows authenticated attackers to execute arbitrary code with system-level privileges on vulnerable Windows systems, potentially leading to complete system compromise across a wide range of Windows client and server operating systems.

Affected Products

• Microsoft Windows 10 (multiple versions including 1607, 1709, 1803, 1809, 1903, 1909, 2004)
• Microsoft Windows 7 SP1
• Microsoft Windows 8.1
• Microsoft Windows RT 8.1
• Microsoft Windows Server 2008 SP2 and R2 SP1
• Microsoft Windows Server 2012 and R2
• Microsoft Windows Server 2016 (including versions 1803, 1903, 1909, 2004)
• Microsoft Windows Server 2019

Discovery Timeline

• June 9, 2020 - CVE-2020-1301 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-1301

Vulnerability Analysis

This vulnerability resides in Microsoft's SMBv1 protocol implementation, a legacy network file sharing protocol that has been the target of numerous high-profile attacks including WannaCry and NotPetya. The flaw occurs in how the SMBv1 server processes incoming requests from authenticated users. When the server receives a malformed or specially crafted request, improper handling of the request data can lead to arbitrary code execution.

The network-accessible nature of this vulnerability makes it particularly dangerous in enterprise environments where SMBv1 may still be enabled for legacy compatibility. An attacker who successfully exploits this vulnerability could gain the same level of access as the SMB service, typically running with elevated system privileges, enabling full compromise of the affected system.

Root Cause

The root cause of this vulnerability lies in improper request handling within the SMBv1 server component of Windows. When processing certain malformed requests, the SMBv1 server fails to properly validate or sanitize input data before processing it, leading to conditions where attacker-controlled data can influence code execution flow. Microsoft has classified this vulnerability without specific CWE information (NVD-CWE-noinfo), indicating the precise technical mechanism has not been publicly disclosed.

Attack Vector

The attack vector for CVE-2020-1301 is network-based, requiring authenticated access to the target system. An attacker must first authenticate to the SMBv1 service before sending the specially crafted request that triggers the vulnerability. This authentication requirement provides some mitigation against anonymous remote attacks, but authenticated users or compromised credentials can still be leveraged for exploitation.

The attack does not require user interaction and can be executed with low complexity once authentication is achieved. Due to the network exposure of SMB services (typically on ports 445 and 139), systems with SMBv1 enabled and accessible from untrusted networks are at significant risk.

The vulnerability is exploited by sending malformed SMB requests to the server. Due to the sensitive nature of SMB exploits and their history of widespread malicious use, specific technical details and proof-of-concept code are not publicly disclosed. See the Microsoft Security Advisory CVE-2020-1301 for official technical guidance.

Detection Methods for CVE-2020-1301

Indicators of Compromise

• Unusual SMB traffic patterns or malformed SMB packets targeting port 445 or 139
• Unexpected process spawning from SMB server processes (e.g., svchost.exe hosting the LanmanServer service)
• System event logs indicating SMBv1 authentication from suspicious or unexpected source addresses
• Memory anomalies or crashes in the SMB server service

Detection Strategies

• Deploy network intrusion detection systems (NIDS) with signatures for malformed SMBv1 requests
• Monitor Windows Security Event logs for unusual SMBv1 authentication events (Event ID 4624 with logon type 3)
• Implement endpoint detection and response (EDR) solutions to detect post-exploitation behaviors following SMB-based attacks
• Audit systems for SMBv1 usage with PowerShell: Get-WindowsOptionalFeature -Online -FeatureName SMB1Protocol

Monitoring Recommendations

• Enable enhanced SMB logging via Group Policy to capture detailed SMB session information
• Configure SIEM alerts for high-volume or anomalous SMB connection attempts from single sources
• Monitor for lateral movement patterns typically associated with SMB-based exploitation
• Track systems where SMBv1 remains enabled and prioritize them for patch deployment

How to Mitigate CVE-2020-1301

Immediate Actions Required

• Apply the Microsoft security update released in June 2020 to all affected systems immediately
• Disable SMBv1 on all systems where it is not required for legacy application compatibility
• Block SMB traffic (ports 445 and 139) at network perimeter firewalls to prevent external exploitation
• Segment networks to limit SMB exposure and contain potential lateral movement

Patch Information

Microsoft has released security updates addressing CVE-2020-1301 as part of the June 2020 Patch Tuesday release. Organizations should obtain and apply the appropriate patches from the Microsoft Security Advisory CVE-2020-1301. Patches are available for all supported versions of Windows, including Windows 7 (with Extended Security Updates), Windows 8.1, Windows 10, and all affected Windows Server versions.

Workarounds

• Disable SMBv1 protocol entirely on systems that do not require it for legacy compatibility
• Implement strict network segmentation to isolate systems that must retain SMBv1 functionality
• Use Windows Firewall rules to restrict SMB access to only authorized systems and networks
• Deploy SentinelOne Singularity to detect and block exploitation attempts in real-time

# Disable SMBv1 on Windows (PowerShell - Run as Administrator)
# For Windows 10/Server 2016 and later:
Disable-WindowsOptionalFeature -Online -FeatureName SMB1Protocol -NoRestart

# For older Windows versions, use DISM:
# dism /online /Disable-Feature /FeatureName:SMB1Protocol

# Verify SMBv1 is disabled:
Get-WindowsOptionalFeature -Online -FeatureName SMB1Protocol

# Block SMB at Windows Firewall (if external access is not needed):
New-NetFirewallRule -DisplayName "Block SMB Inbound" -Direction Inbound -LocalPort 445 -Protocol TCP -Action Block