CVE-2025-21391: Microsoft Windows Storage Link Following Vulnerability

What it is

Windows Storage Elevation of Privilege Vulnerability

Exploitation evidence

First exploit evidence seen: 2025-02-11 (earliest date across the sources below).

Exploited in the wild

• CISA KEV: listed since 2025-02-11. Source

Sources: CISA KEV.

How to fix it

CISA required action

Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable. (source: CISA KEV)

Fixed versions

• microsoft windows 10 1507: upgrade to 10.0.10240.20915 or later
• microsoft windows 10 1607: upgrade to 10.0.14393.7785 or later
• microsoft windows 10 1809: upgrade to 10.0.17763.6893 or later
• microsoft windows 10 21h2: upgrade to 10.0.19044.5487 or later
• microsoft windows 10 22h2: upgrade to 10.0.19045.5487 or later
• microsoft windows 11 22h2: upgrade to 10.0.22621.4890 or later
• microsoft windows 11 23h2: upgrade to 10.0.22631.4890 or later
• microsoft windows 11 24h2: upgrade to 10.0.26100.3107 or later
• microsoft windows server 2016: upgrade to 10.0.14393.7785 or later
• microsoft windows server 2019: upgrade to 10.0.17763.6893 or later
• microsoft windows server 2022: upgrade to 10.0.20348.3148 or later
• microsoft windows server 2022 23h2: upgrade to 10.0.25398.1425 or later
• microsoft windows server 2025: upgrade to 10.0.26100.3107 or later

Derived from the NVD CPE configuration (versionEndExcluding / versionEndIncluding). Always confirm with the vendor advisory.

Vendor advisories and patches

• https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-21391 (CISA KEV notes)

MITRE ATT&CK mitigations for this chain

• M1051 Update Software (for T1068) : Update software regularly by employing patch management for internal enterprise endpoints and servers.
• M1050 Exploit Protection (for T1068) : Security applications that look for behavior used during exploitation such as Windows Defender Exploit Guard (WDEG) and the Enhanced Mitigation Experience Toolkit (EMET) can be used to mitigate some exploitation behavior. Control flow integrity checking is another way to potentially identify and stop a software exploi
• M1048 Application Isolation and Sandboxing (for T1068) : Make it difficult for adversaries to advance their operation through exploitation of undiscovered or unpatched vulnerabilities by using sandboxing. Other types of virtualization and application microsegmentation may also mitigate the impact of some types of exploitation. Risks of additional exploits and weaknesses in t
• M1019 Threat Intelligence Program (for T1068) : Develop a robust cyber threat intelligence capability to determine what types and levels of threat may use software exploits and 0-days against a particular organization.
• M1038 Execution Prevention (for T1068, T1490) : Consider blocking the execution of known vulnerable drivers that adversaries may exploit to execute code in kernel mode. Validate driver block rules in audit mode to ensure stability prior to production deployment.
• M1032 Multi-factor Authentication (for T1485) : Implement multi-factor authentication (MFA) delete for cloud storage resources, such as AWS S3 buckets, to prevent unauthorized deletion of critical data and infrastructure. MFA delete requires additional authentication steps, making it significantly more difficult for adversaries to destroy data without proper credent
• M1053 Data Backup (for T1485, T1490) : Consider implementing IT disaster recovery plans that contain procedures for taking regular data backups that can be used to restore organizational data. Ensure backups are stored off system and protected from common methods adversaries may use to gain access and destroy the backups to prevent recovery.
• M1018 User Account Management (for T1485, T1490) : In cloud environments, limit permissions to modify cloud bucket lifecycle policies (e.g., `PutLifecycleConfiguration` in AWS) to only those accounts that require it. In AWS environments, consider using Service Control policies to limit the use of the `PutBucketLifecycle` API call.
• M1028 Operating System Configuration (for T1490) : Consider technical controls to prevent the disabling of services or deletion of files involved in system recovery. Additionally, ensure that WinRE is enabled using the following command: <code>reagentc /enable</code>.

Detection Generic guidance

• Privilege Escalation: Alert on processes gaining SYSTEM/root unexpectedly, and on exploitation crashes of privileged services.
• Impact: Monitor service availability, unexpected encryption activity and mass file changes.

Response checklist Generic guidance

1. Inventory: find every instance of the affected product and version (include internet-facing and forgotten ones).
2. Patch or mitigate per the vendor advisory; if you cannot patch, remove internet exposure or apply the vendor workaround.
3. Assume compromise if the system was exposed before patching: hunt for the indicators in the advisory and review logs back to the disclosure date.
4. Rotate credentials and secrets stored on or used by the affected system if compromise cannot be ruled out.