CVE-2026-26131
📋 TL;DR
This CVE describes an incorrect default permissions vulnerability in .NET that allows an authenticated attacker to escalate privileges on the local system. It affects systems running vulnerable versions of .NET where an attacker already has some level of access. The vulnerability enables local privilege escalation from a lower-privileged account to higher system privileges.
💻 Affected Systems
- .NET Framework
- .NET Core
- .NET
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
An authenticated attacker gains SYSTEM/root privileges, enabling complete system compromise, data theft, persistence establishment, and lateral movement across the network.
Likely Case
An attacker with initial access (such as a standard user account) escalates to administrative privileges, allowing them to install malware, disable security controls, and access sensitive data.
If Mitigated
With proper access controls, least privilege principles, and network segmentation, impact is limited to the compromised host with reduced lateral movement potential.
🎯 Exploit Status
Requires authenticated access; exploitation likely involves manipulating file permissions or registry keys to achieve privilege escalation.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: To be specified in Microsoft security update
Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-26131
Restart Required: Yes
Instructions:
1. Apply the latest .NET security update from Microsoft. 2. Restart affected systems. 3. Verify the update was successfully installed.
🔧 Temporary Workarounds
Implement Least Privilege Access
allRestrict user permissions to minimum required levels to reduce attack surface.
Harden File and Registry Permissions
windowsReview and tighten permissions on .NET installation directories and registry keys.
icacls "C:\Program Files\dotnet" /inheritance:r /grant:r "SYSTEM:(OI)(CI)F" "Administrators:(OI)(CI)F"
Set-Acl -Path "HKLM:\SOFTWARE\Microsoft\.NETFramework" -AclObject (Get-Acl -Path "HKLM:\SOFTWARE\Microsoft\.NETFramework")
🧯 If You Can't Patch
- Implement strict access controls and monitor for privilege escalation attempts
- Isolate vulnerable systems in segmented network zones with limited trust
🔍 How to Verify
Check if Vulnerable:
Check .NET version and compare against patched versions in Microsoft advisoryCheck Version:
dotnet --version (for .NET Core/5+) or check registry/installed programs for .NET FrameworkVerify Fix Applied:
Verify .NET version matches or exceeds patched version specified in Microsoft update📡 Detection & Monitoring
Log Indicators:
- Unexpected privilege escalation events in Windows Security logs (Event ID 4672, 4688)
- Suspicious access to .NET directories or registry keys by non-admin users
Network Indicators:
- Unusual outbound connections from previously low-privileged accounts
- Lateral movement attempts from compromised hosts
SIEM Query:
source="windows_security" event_id=4672 OR event_id=4688 | where user_account!="SYSTEM" AND user_account!="Administrator" | stats count by host, user_account