CyberSecBulletin
CVE-2026-21525Exploited in the wildNVD status: Analyzed

Microsoft Windows NULL Pointer Dereference

Published Updated By the CyberSecBulletin desk

CVE-2026-21525 is a medium-severity NULL pointer dereference vulnerability in Windows 10 Version 1607 from Microsoft, with a CVSS 3.1 base score of 6.2 out of 10. It can be exploited with local access to the system by an unauthenticated attacker, without any action from a user. 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.

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
LocalThe attacker needs local access or must trick a user into running something.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
NoneNo account or login is needed.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
NoneNo data is disclosed.
Integrity
NoneNothing can be modified.
Availability
HighThe component can be taken down completely.

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

Official description

Null pointer dereference in Windows Remote Access Connection Manager allows an unauthorized attacker to deny service locally.

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

The underlying weakness: NULL Pointer Dereference

The product dereferences a pointer that it expects to be valid but is NULL.

How developers prevent this class of flaw

  • For any pointers that could have been modified or provided from a function that can return NULL, check the pointer for NULL before use. When working with a multithreaded or otherwise asynchronous environment, ensure that proper locking APIs are used to lock before the check, and unlock when it has finished.
  • Select a programming language that is not susceptible to these issues.
  • Check the results of all functions that return a value and verify that the value is non-null before acting upon it.

More NULL Pointer Dereference vulnerabilities (CWE-476)

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: partial).
  4. Deadline for US federal agencies to remediate, set by CISA.
  5. Record last changed materially (score, affected products, status or references).

References

Recent NULL Pointer Dereference vulnerabilities

Spotted an error? Tell us.