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CVE-2020-0646

From Exploited flaws, HARD’s guide to the flaws being used in attacks · Checked
This article is about a flaw in Microsoft .NET Framework. For every flaw being used in attacks, see Exploited flaws; for Microsoft’s, see Microsoft flaws being used in attacks.

CVE-2020-0646 is a security flaw in Microsoft .NET Framework, the framework many Windows apps are built on. Attackers can run their own code on Microsoft .NET Framework. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 3 Nov 2021.[1]

Microsoft .NET Framework is in things households have, such as phones, computers, browsers and everyday apps, so the fix matters at home as much as at work. Microsoft has published a fix or advice.

Description

CISA calls it a remote code execution in Microsoft .NET Framework. In its words: “Microsoft .NET Framework contains an improper input validation vulnerability that allows for remote code execution.”[1]

The CVE record adds: “A remote code execution vulnerability exists when the Microsoft .NET Framework fails to validate input properly, aka '.NET Framework Remote Code Execution Injection Vulnerability'.”[2]

The underlying weakness is CWE-91, in MITRE’s list of common software weaknesses.

It scores 9.8 out of 10 on the Common Vulnerability Scoring System, which rates it critical, scored by NVD using CVSS 3.1.[2]

Affected versions

NVD’s record doesn’t list version ranges for it; Microsoft’s advisory has them[3]. CISA names the product as Microsoft .NET Framework.

Every device with Microsoft .NET Framework needs the update.

Exploitation

CISA added it to its catalog of known exploited vulnerabilities on 3 Nov 2021, 659 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 3 May 2022 to fix it.[1]

FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 99%. That’s in the top 1% of the flaws it scores.[4]

CISA assesses it as automatable: attackers can run it against many targets at once.

CISA doesn’t say who was attacked, or how.

Fix

Microsoft has published a fix or advice.[3] CISA’s required action: “Apply updates per vendor instructions.”[1]

  1. Update Microsoft .NET Framework now.Install the latest update from Microsoft on every device that has it, and restart when asked. Then turn on automatic updates, so the next fix arrives on its own.
  2. If there’s no update, stop using it.CISA’s advice when a flaw being used in attacks has no fix is to stop using the product until it does.

Timeline

DateEvent
The flaw is made public in the National Vulnerability Database, with a severity score of 9.8.[2]
CISA adds it to its catalog of flaws known to be used in attacks.[1]
CISA’s deadline for US government agencies to fix it.[1]
FIRST puts the odds of it being used in attacks in the next 30 days at 99%.[4]

See also

Other Microsoft .NET Framework flaws

Other Microsoft flaws

  • CVE-2026-96951, Microsoft Windows: command injection ·
  • CVE-2026-65660, Microsoft SharePoint: code injection ·
  • CVE-2026-85880, Microsoft Windows: heap-based buffer overflow ·
  • CVE-2026-81963, Microsoft Windows: link following ·
  • CVE-2019-1068, Microsoft SQL Server: remote code execution ·

Added the same day

  • CVE-2021-42258, BQE BillQuick Web Suite: SQL injection ·
  • CVE-2021-42013, Apache HTTP Server: path traversal ·
  • CVE-2021-41773, Apache HTTP Server: path traversal ·
  • CVE-2021-40539, Zoho ManageEngine: aDSelfService plus authentication bypass ·
  • CVE-2021-40444, Microsoft MSHTML: remote code execution ·

Every Microsoft flaw on CISA’s list · Everything added in November 2021

References

  1. ^ Cybersecurity and Infrastructure Security Agency. “Microsoft .NET Framework Remote Code Execution Vulnerability”. Known Exploited Vulnerabilities Catalog, added 3 Nov 2021.
  2. ^ National Institute of Standards and Technology. “CVE-2020-0646 Detail”. National Vulnerability Database, published 14 Jan 2020.
  3. ^ Microsoft. Advisories and fixes: portal.msrc.microsoft.com.
  4. ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.992, percentile 99.9, 31 Oct 2026.
  5. CVE Program. “CVE-2020-0646”. The official CVE record.

This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.