CVE-2026-62871: Microsoft .NET RCE Vulnerability

CVE-2026-62871 Overview

CVE-2026-62871 is an out-of-bounds write vulnerability [CWE-122] in Microsoft .NET that allows an unauthorized attacker to execute code locally. The flaw affects .NET runtime components shipped with Windows, macOS, and Linux, as well as Visual Studio 2022 and Visual Studio 2026. Exploitation requires user interaction on the target system. Successful exploitation leads to full compromise of confidentiality, integrity, and availability on the affected host. Microsoft published the advisory on August 11, 2026, and updated it on August 13, 2026.

Critical Impact
An attacker who convinces a user to open a crafted file or run a malicious .NET payload can execute arbitrary code in the context of the current user, resulting in local host compromise.

Affected Products

Microsoft .NET (multiple versions across Windows, macOS, and Linux)
Microsoft Visual Studio 2022
Microsoft Visual Studio 2026

Discovery Timeline

2026-08-11 - CVE-2026-62871 published to NVD
2026-08-11 - Microsoft releases security update for CVE-2026-62871
2026-08-13 - Last updated in NVD database

Technical Details for CVE-2026-62871

Vulnerability Analysis

CVE-2026-62871 is a heap-based out-of-bounds write in the .NET runtime. The runtime writes data beyond the bounds of an allocated buffer on the heap, corrupting adjacent memory structures. An attacker who controls the size or contents of the input that triggers the flawed write can overwrite object headers, function pointers, or vtable entries within the .NET process.

Exploitation requires local access and user interaction, meaning the victim must open a crafted file, load a malicious assembly, or run a hostile project in Visual Studio. Because the attack executes in the context of the running .NET process, the attacker inherits the privileges of the current user. This includes access to user files, credentials cached by the process, and any tokens the process holds.

The vulnerability spans .NET installations on Windows, macOS, and Linux, indicating the defect lies in cross-platform runtime code rather than a platform-specific loader. Visual Studio 2022 and 2026 are affected because they bundle vulnerable .NET components.

Root Cause

The root cause is missing or incorrect bounds validation before a heap write inside the .NET runtime. When the runtime processes attacker-controlled input, it computes a destination offset or length that exceeds the allocated buffer, producing a classic heap corruption primitive [CWE-122].

Attack Vector

The attack vector is local with required user interaction. An attacker delivers a malicious file, assembly, or project that the victim opens with an affected .NET runtime or Visual Studio instance. Delivery channels include phishing attachments, malicious Git repositories, and NuGet packages containing crafted payloads.

No verified public exploit code exists for CVE-2026-62871 at the time of writing. Refer to the Microsoft Security Update CVE-2026-62871 for authoritative technical details.

Detection Methods for CVE-2026-62871

Indicators of Compromise

Unexpected dotnet.exe, dotnet, or devenv.exe child processes spawning shells, powershell.exe, or cmd.exe shortly after a user opens a file or project.
Crash dumps or Windows Error Reporting entries referencing access violations inside coreclr.dll, clrjit.dll, or System.Private.CoreLib.
Unsigned or unusual .NET assemblies loaded from user-writable directories such as %TEMP%, %APPDATA%, or /tmp.

Detection Strategies

Hunt for .NET processes performing outbound network connections or writing to autorun locations immediately after project or file open events.
Correlate Visual Studio and dotnet process launches with subsequent LOLBin execution such as rundll32.exe, regsvr32.exe, or bash invocations.
Alert on newly registered NuGet feeds or MSBuild task assemblies loaded from untrusted paths.

Monitoring Recommendations

Enable EDR telemetry for module loads and child-process creation on all developer workstations and build servers.
Monitor authenticode signatures on .NET runtime binaries and flag installations that diverge from the patched baseline.
Track opening of .sln, .csproj, .dll, and .nupkg files sourced from email, chat, or untrusted repositories.

How to Mitigate CVE-2026-62871

Immediate Actions Required

Apply the Microsoft security update referenced in MSRC advisory CVE-2026-62871 to all Windows, macOS, and Linux hosts running .NET.
Update Visual Studio 2022 and Visual Studio 2026 to the latest release through the Visual Studio Installer.
Inventory build agents, CI/CD runners, and developer laptops to confirm every .NET SDK and runtime version is patched.

Patch Information

Microsoft has released fixes for CVE-2026-62871 across supported .NET versions and Visual Studio 2022 and 2026. Consult the Microsoft Security Update CVE-2026-62871 for the specific build numbers that address the out-of-bounds write. On Linux, update through the distribution package manager or the Microsoft package feed. On macOS, install the updated dotnet-sdk and dotnet-runtime packages.

Workarounds

Restrict execution of untrusted .NET assemblies and projects on developer and end-user systems until patching completes.
Use application allow-listing to block dotnet execution of binaries from user-writable directories.
Train users to avoid opening .sln, .csproj, or .dll files received from untrusted sources.

bash

# Verify installed .NET runtime versions on Linux/macOS
dotnet --list-runtimes
dotnet --list-sdks

# Windows: check installed .NET versions
dotnet --info

# After applying the Microsoft update, confirm the runtime version
# matches the patched build listed in the MSRC advisory for CVE-2026-62871