# CVE-2020-1284: Windows SMBv3 Client/Server Denial of Service Vulnerability

CVE-2020-1284 is fixed in 4 products on 1 platform, first by KB4557957, released June 9, 2020. It is not reported as exploited, but the vendor rates exploitation more likely. Patch Radar priority: Urgent.

- Web page: https://patchblox.com/security/cve/CVE-2020-1284
- Priority: Urgent
- CVSS: 7.5 (Important)
- EPSS: 0.0705
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Vendor exploitability assessment: Exploitation More Likely
- Published: Jun 9, 2020
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2020-1284

## Description

<p>A denial of service vulnerability exists in the way that the Microsoft Server Message Block 3.1.1 (SMBv3) protocol handles certain requests. An authenticated attacker who successfully exploited this vulnerability against an SMB Server could cause the affected system to crash. An unauthenticated attacker could also exploit this this vulnerability against an SMB client and cause the affected system to crash.</p> <p>To exploit the vulnerability against a server, an authenticated attacker could send a specially crafted packet to a targeted SMBv3 server. To exploit the vulnerability against a client, an unauthenticated attacker would need to configure a malicious SMBv3 server and convince a user to connect to it.</p> <p>The security update addresses the vulnerability by correcting how the SMBv3 protocol handles these specially crafted requests.</p>

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Microsoft | Windows 10 Version 2004 for 32-bit Systems | 19041.329 | [KB4557957](https://patchblox.com/security/data/fix/microsoft/kb4557957.md) | Jun 9, 2020 |
| Microsoft | Windows 10 Version 2004 for ARM64-based Systems | 19041.329 | [KB4557957](https://patchblox.com/security/data/fix/microsoft/kb4557957.md) | Jun 9, 2020 |
| Microsoft | Windows 10 Version 2004 for x64-based Systems | 19041.329 | [KB4557957](https://patchblox.com/security/data/fix/microsoft/kb4557957.md) | Jun 9, 2020 |
| Microsoft | Windows Server, version 2004 (Server Core installation) | 19041.329 | [KB4557957](https://patchblox.com/security/data/fix/microsoft/kb4557957.md) | Jun 9, 2020 |

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Data as of 2026-11-08T00:53:09Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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