CVE-2026-65810 Overview
CVE-2026-65810 is a relative path traversal vulnerability in Microsoft .NET Framework that enables local privilege escalation. An unauthorized attacker with local access can leverage improper path handling to elevate privileges on affected systems. The flaw is classified under [CWE-23] (Relative Path Traversal) and requires user interaction to trigger successful exploitation.
Critical Impact
A local attacker who convinces a user to interact with a crafted file or path can gain elevated privileges, resulting in high impact to confidentiality, integrity, and availability of the host.
Affected Products
- Microsoft .NET Framework (specific supported versions per Microsoft advisory)
- Windows systems with vulnerable .NET Framework runtimes installed
- Applications built on affected .NET Framework versions
Discovery Timeline
- 2026-08-11 - CVE-2026-65810 published to the National Vulnerability Database (NVD)
- 2026-08-12 - Last updated in NVD database
Technical Details for CVE-2026-65810
Vulnerability Analysis
The vulnerability stems from improper validation of file path inputs within .NET Framework components. When a component resolves a relative path, it fails to normalize sequences such as ..\ before performing file operations. An attacker can craft input that escapes the intended directory scope. This allows the attacker to redirect file operations to privileged locations controlled by higher-integrity processes.
Successful exploitation requires local access and user interaction. Once triggered, the flaw enables the attacker to place or manipulate files in locations they should not reach. The result is code execution or file replacement in the context of a higher-privileged process. Impact spans confidentiality, integrity, and availability.
Root Cause
The root cause is insufficient canonicalization of relative path segments in .NET Framework file-handling logic. The affected code paths accept user-influenced strings and pass them to file APIs without stripping traversal sequences. This maps directly to the [CWE-23] weakness class. Microsoft's advisory documents the affected components and patched versions.
Attack Vector
Attackers exploit CVE-2026-65810 through a local vector that requires user interaction. A typical scenario involves a low-privileged user opening a crafted archive, project file, or configuration payload processed by a vulnerable .NET Framework component. The component then writes or reads outside the intended directory, targeting paths used by higher-privileged services. The attacker leverages this file operation to overwrite trusted binaries, drop DLLs into search paths, or manipulate configuration used by SYSTEM-level processes.
No public proof-of-concept exploit is available at time of publication. Refer to the Microsoft Security Update Guide for authoritative technical details on the affected components and exploitation preconditions.
Detection Methods for CVE-2026-65810
Indicators of Compromise
- File creation or modification events in system directories originating from .NET Framework processes such as dotnet.exe, mscorsvw.exe, or application hosts running as elevated users
- Presence of traversal sequences (..\ or ..%2F) in file paths passed to .NET applications through command lines, archives, or project files
- Unexpected DLLs or executables written to directories used by privileged services shortly after a user opens a document or archive
Detection Strategies
- Monitor process telemetry for .NET Framework binaries performing file writes to C:\Windows\System32, Program Files, or service-owned directories
- Correlate user interaction events (file open, archive extraction) with subsequent privilege transitions to SYSTEM or elevated service accounts
- Inspect archives, .csproj, .sln, and configuration files handled by build or runtime tooling for embedded relative path traversal patterns
Monitoring Recommendations
- Enable Windows audit policies for file system object access on sensitive directories and forward events to a centralized log platform
- Track child-process creation from .NET Framework hosts and flag execution originating from user-writable paths
- Alert on integrity-level transitions where a medium-integrity process influences file operations executed by a high-integrity service
How to Mitigate CVE-2026-65810
Immediate Actions Required
- Apply the Microsoft security update referenced in the Microsoft Security Update Guide for CVE-2026-65810 across all systems running affected .NET Framework versions
- Inventory endpoints and servers to identify installed .NET Framework versions and prioritize patch deployment on multi-user and privileged systems
- Restrict local logon rights on high-value hosts to reduce the population of accounts capable of triggering the local attack vector
Patch Information
Microsoft has published guidance and updates via the Microsoft Security Response Center. Administrators should consult the Microsoft Security Update Guide entry for CVE-2026-65810 to identify the correct cumulative update for each affected .NET Framework version and Windows release. Apply updates through Windows Update, WSUS, or the Microsoft Update Catalog according to standard change management procedures.
Workarounds
- No official vendor workaround is documented; patching is the supported remediation path
- Reduce exposure by blocking untrusted archives, project files, and configuration payloads from being opened by users on systems where the update has not yet been deployed
- Enforce application allowlisting to prevent execution of binaries written to non-standard locations by exploited .NET components
# Verify installed .NET Framework release on Windows hosts
reg query "HKLM\SOFTWARE\Microsoft\NET Framework Setup\NDP\v4\Full" /v Release
# Deploy the Microsoft security update via PowerShell (example)
wusa.exe C:\Updates\windows10.0-kb-x64.msu /quiet /norestart
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
