Windows 10 Version 1507: Time-of-check Time-of-use (TOCTOU) Race Condition
CVE-2025-21191 is a high-severity time-of-check time-of-use (TOCTOU) race condition vulnerability in Windows 10 Version 1507 from Microsoft, with a CVSS 3.1 base score of 7.0 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists version 10.0.10240.20978 as the first without the flaw, so updating Windows 10 Version 1507 to that release or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.32% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Windows 10 Version 1507 to 10.0.10240.20978 or a later version.
- Update Windows 10 Version 1607 to 10.0.14393.7969 or a later version.
- Update Windows 10 Version 1809 to 10.0.17763.7136 or a later version.
- Read the advisory on msrc.microsoft.com for workarounds and exact fixed builds.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Microsoft | Windows 10 Version 1507 | 10.0.10240.0 up to, but not including, 10.0.10240.20978 | 10.0.10240.20978 |
| Microsoft | Windows 10 Version 1607 | 10.0.14393.0 up to, but not including, 10.0.14393.7969 | 10.0.14393.7969 |
| Microsoft | Windows 10 Version 1809 | 10.0.17763.0 up to, but not including, 10.0.17763.7136 | 10.0.17763.7136 |
| Microsoft | Windows 10 Version 21H2 | 10.0.19044.0 up to, but not including, 10.0.19044.5737 | 10.0.19044.5737 |
| Microsoft | Windows 10 Version 22H2 | 10.0.19045.0 up to, but not including, 10.0.19045.5737 | 10.0.19045.5737 |
| Microsoft | Windows 11 version 22H2 | 10.0.22621.0 up to, but not including, 10.0.22621.5189 | 10.0.22621.5189 |
| Microsoft | Windows 11 version 22H3 | 10.0.22631.0 up to, but not including, 10.0.22631.5189 | 10.0.22631.5189 |
| Microsoft | Windows 11 Version 23H2 | 10.0.22631.0 up to, but not including, 10.0.22631.5189 | 10.0.22631.5189 |
| Microsoft | Windows 11 Version 24H2 | 10.0.26100.0 up to, but not including, 10.0.26100.3775 | 10.0.26100.3775 |
| Microsoft | Windows Server 2008 R2 Service Pack 1 | 6.1.7601.0 up to, but not including, 6.1.7601.27670 | 6.1.7601.27670 |
| Microsoft | Windows Server 2008 R2 Service Pack 1 (Server Core installation) | 6.1.7601.0 up to, but not including, 6.1.7601.27670 | 6.1.7601.27670 |
| Microsoft | Windows Server 2008 Service Pack 2 | 6.0.6003.0 up to, but not including, 6.0.6003.23220 | 6.0.6003.23220 |
| Microsoft | Windows Server 2008 Service Pack 2 (Server Core installation) | 6.0.6003.0 up to, but not including, 6.0.6003.23220 | 6.0.6003.23220 |
| Microsoft | Windows Server 2012 | 6.2.9200.0 up to, but not including, 6.2.9200.25423 | 6.2.9200.25423 |
| Microsoft | Windows Server 2012 (Server Core installation) | 6.2.9200.0 up to, but not including, 6.2.9200.25423 | 6.2.9200.25423 |
| Microsoft | Windows Server 2012 R2 | 6.3.9600.0 up to, but not including, 6.3.9600.22523 | 6.3.9600.22523 |
| Microsoft | Windows Server 2012 R2 (Server Core installation) | 6.3.9600.0 up to, but not including, 6.3.9600.22523 | 6.3.9600.22523 |
| Microsoft | Windows Server 2016 | 10.0.14393.0 up to, but not including, 10.0.14393.7969 | 10.0.14393.7969 |
| Microsoft | Windows Server 2016 (Server Core installation) | 10.0.14393.0 up to, but not including, 10.0.14393.7969 | 10.0.14393.7969 |
| Microsoft | Windows Server 2019 | 10.0.17763.0 up to, but not including, 10.0.17763.7136 | 10.0.17763.7136 |
| Microsoft | Windows Server 2019 (Server Core installation) | 10.0.17763.0 up to, but not including, 10.0.17763.7136 | 10.0.17763.7136 |
| Microsoft | Windows Server 2022 | 10.0.20348.0 up to, but not including, 10.0.20348.3453 | 10.0.20348.3453 |
| Microsoft | Windows Server 2022, 23H2 Edition (Server Core installation) | 10.0.25398.0 up to, but not including, 10.0.25398.1551 | 10.0.25398.1551 |
| Microsoft | Windows Server 2025 | 10.0.26100.0 up to, but not including, 10.0.26100.3775 | 10.0.26100.3775 |
| Microsoft | Windows Server 2025 (Server Core installation) | 10.0.26100.0 up to, but not including, 10.0.26100.3775 | 10.0.26100.3775 |
Version data comes from the organisation that assigned the CVE; 10 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
- HighSuccess depends on conditions outside the attacker's control.
- Privileges required
- LowA basic user account is enough.
- User interaction
- NoneNo action by a victim is required.
- 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:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by CNA (microsoft.com).
Official description
Time-of-check time-of-use (toctou) race condition in Windows Local Security Authority (LSA) allows an authorized attacker to elevate privileges locally.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Time-of-check Time-of-use (TOCTOU) Race Condition
The product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check.
How developers prevent this class of flaw
- The most basic advice for TOCTOU vulnerabilities is to not perform a check before the use. This does not resolve the underlying issue of the execution of a function on a resource whose state and identity cannot be assured, but it does help to limit the false sense of security given by the check.
- When the file being altered is owned by the current user and group, set the effective gid and uid to that of the current user and group when executing this statement.
- Limit the interleaving of operations on files from multiple processes.
More Time-of-check Time-of-use (TOCTOU) Race Condition vulnerabilities (CWE-367)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Other vulnerabilities in Windows 10 Version 1507
- 7.0 High severity
- 7.8 High severity
- 7.0 High severity
- 7.7 High severity
- 7.0 High severity
Recent Time-of-check Time-of-use (TOCTOU) Race Condition vulnerabilities
- 7.0 High severity
- 8.6 High severity
- 8.2 High severity
- 7.5 High severity
- 8.1 High severity
- 7.0 High severity
Spotted an error? Tell us.