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CVE-2020-1350

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

CVE-2020-1350 is a security flaw in Microsoft Windows, Microsoft’s operating system for PCs and servers. Attackers can run their own code on Microsoft Windows. 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 Windows 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 DNS server remote code execution in Microsoft Windows. In its words: “Microsoft Windows DNS Servers fail to properly handle requests, allowing an attacker to perform remote code execution in the context of the Local System Account. The vulnerability is also known under the moniker of SIGRed.”[1]

The underlying weakness is improper input validation (CWE-20), in MITRE’s list of common software weaknesses.[2]

It scores 10.0 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 Windows.

Every device with Microsoft Windows needs the update.

Exploitation

CISA added it to its catalog of known exploited vulnerabilities on 3 Nov 2021, 477 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 97%. 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 Windows now.On Windows: Settings, Windows Update, Check for updates, then restart. Office updates come the same way, or from any Office app: File, Account, Update Options. 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 10.0.[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 97%.[4]

See also

Other Microsoft Windows flaws

Other improper input validation flaws

  • CVE-2026-93952, Arista VeloCloud Orchestrator: improper input validation ·
  • CVE-2026-12569, PTC Windchill and FlexPLM: improper input validation ·
  • CVE-2026-34910, Ubiquiti UniFi OS: improper input validation ·
  • CVE-2026-6973, Ivanti Endpoint Manager Mobile (EPMM): improper input validation ·
  • CVE-2026-34197, Apache ActiveMQ: improper input validation ·

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 Windows DNS Server Remote Code Execution Vulnerability”. Known Exploited Vulnerabilities Catalog, added 3 Nov 2021.
  2. ^ National Institute of Standards and Technology. “CVE-2020-1350 Detail”. National Vulnerability Database, published 14 Jul 2020.
  3. ^ Microsoft. Advisories and fixes: portal.msrc.microsoft.com.
  4. ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.967, percentile 99.9, 31 Oct 2026.
  5. CVE Program. “CVE-2020-1350”. 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.