CyberSecBulletin
CVE-2026-21510Exploited in the wildNVD status: Analyzed

Microsoft Windows Shell Protection Mechanism Failure

Published Updated By the CyberSecBulletin desk

CVE-2026-21510 is a high-severity protection mechanism failure vulnerability in Windows 10 Version 1607 from Microsoft, with a CVSS 3.1 base score of 8.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, but only if a user takes part, for example by opening a link or file. The record lists version 10.0.14393.8868 as the first without the flaw, so updating Windows 10 Version 1607 to that release or later removes the exposure. CISA added it to the Known Exploited Vulnerabilities catalogue on February 10, 2026, which means attacks have been observed in the wild.

Patch now

Attackers are already exploiting this vulnerability, according to CISA.

What to do

  1. Update Windows 10 Version 1607 to 10.0.14393.8868 or a later version.
  2. Update Windows 10 Version 1809 to 10.0.17763.8389 or a later version.
  3. Update Windows 10 Version 21H2 to 10.0.19044.6937 or a later version.
  4. CISA's required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
  5. Read the advisory on msrc.microsoft.com for workarounds and exact fixed builds.
  6. Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
  7. Because the attack needs a user to take part, warn users about unexpected links and files related to this product until it is patched.

Affected products and versions

VendorProductAffected versionsFixed in
MicrosoftWindows 10 Version 160710.0.14393.0 up to, but not including, 10.0.14393.886810.0.14393.8868
MicrosoftWindows 10 Version 180910.0.17763.0 up to, but not including, 10.0.17763.838910.0.17763.8389
MicrosoftWindows 10 Version 21H210.0.19044.0 up to, but not including, 10.0.19044.693710.0.19044.6937
MicrosoftWindows 10 Version 22H210.0.19045.0 up to, but not including, 10.0.19045.693710.0.19045.6937
MicrosoftWindows 11 version 22H310.0.22631.0 up to, but not including, 10.0.22631.664910.0.22631.6649
MicrosoftWindows 11 Version 23H210.0.22631.0 up to, but not including, 10.0.22631.664910.0.22631.6649
MicrosoftWindows 11 Version 24H210.0.26100.0 up to, but not including, 10.0.26100.784010.0.26100.7840
MicrosoftWindows 11 Version 25H210.0.26200.0 up to, but not including, 10.0.26200.784010.0.26200.7840
MicrosoftWindows 11 version 26H110.0.28000.0 up to, but not including, 10.0.28000.157510.0.28000.1575
MicrosoftWindows Server 20126.2.9200.0 up to, but not including, 6.2.9200.259236.2.9200.25923
MicrosoftWindows Server 2012 (Server Core installation)6.2.9200.0 up to, but not including, 6.2.9200.259236.2.9200.25923
MicrosoftWindows Server 2012 R26.3.9600.0 up to, but not including, 6.3.9600.230226.3.9600.23022
MicrosoftWindows Server 2012 R2 (Server Core installation)6.3.9600.0 up to, but not including, 6.3.9600.230226.3.9600.23022
MicrosoftWindows Server 201610.0.14393.0 up to, but not including, 10.0.14393.886810.0.14393.8868
MicrosoftWindows Server 2016 (Server Core installation)10.0.14393.0 up to, but not including, 10.0.14393.886810.0.14393.8868
MicrosoftWindows Server 201910.0.17763.0 up to, but not including, 10.0.17763.838910.0.17763.8389
MicrosoftWindows Server 2019 (Server Core installation)10.0.17763.0 up to, but not including, 10.0.17763.838910.0.17763.8389
MicrosoftWindows Server 202210.0.20348.0 up to, but not including, 10.0.20348.477310.0.20348.4773
MicrosoftWindows Server 2022, 23H2 Edition (Server Core installation)10.0.25398.0 up to, but not including, 10.0.25398.214910.0.25398.2149
MicrosoftWindows Server 202510.0.26100.0 up to, but not including, 10.0.26100.3237010.0.26100.32370
MicrosoftWindows Server 2025 (Server Core installation)10.0.26100.0 up to, but not including, 10.0.26100.3237010.0.26100.32370
MicrosoftWindows 10 1607before 10.0.14393.886810.0.14393.8868
MicrosoftWindows 10 1809before 10.0.17763.838910.0.17763.8389
MicrosoftWindows 10 21h2before 10.0.19044.693710.0.19044.6937
MicrosoftWindows 10 22h2before 10.0.19045.693710.0.19045.6937

Version data comes from the organisation that assigned the CVE; 4 further products are omitted here. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
NetworkCan be exploited remotely over a network, including the internet.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
NoneNo account or login is needed.
User interaction
RequiredA user must take an action such as opening a file or link.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
HighData or code can be modified at will.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H. Scored by CNA (microsoft.com).

Official description

Protection mechanism failure in Windows Shell allows an unauthorized attacker to bypass a security feature over a network.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Protection Mechanism Failure

The product does not use or incorrectly uses a protection mechanism that provides sufficient defense against directed attacks against the product.

More Protection Mechanism Failure vulnerabilities (CWE-693)

Timeline

  1. CVE record published.
  2. Added to CISA's Known Exploited Vulnerabilities catalogue.
  3. CISA published its SSVC assessment (exploitation: active, automatable: no, technical impact: total).
  4. Deadline for US federal agencies to remediate, set by CISA.
  5. Record last changed materially (score, affected products, status or references).

References

Third-party and government advisories

Recent Protection Mechanism Failure vulnerabilities

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