CVE-2026-69439

Overview

.NET is a free, open-source, cross-platform framework for building modern apps and powerful cloud services. It consists of a runtime and a developer platform made up of tools, programming languages, and libraries for building many different types of applications.

An elevation of privilege vulnerability (CVE-2026-69439) has been identified in Microsoft.DiaSymReader.Native, the native symbol reader that the .NET shared framework carries on Windows. Microsoft describes the issue as an out of bounds write that can occur when parsing a Portable PDB file. HeroDevs investigation traced the .NET 6 exposure to the runtime's MicrosoftDiaSymReaderNativeVersion pin, which has sat inside the advisory's range since Microsoft's final .NET 6.0 release.

Per CWE-122: Heap-based Buffer Overflow, the weakness is a buffer overflow in which the buffer that is overwritten is allocated on the heap.

Every .NET 6 release up to and including NES for .NET 6.0.45 carries an affected version of the component. It ships in-box in the Microsoft.NETCore.App shared framework rather than as an opt-in package, and it is Windows-only, so Linux and macOS layouts do not carry it at all. Exploitation requires user interaction: something must read a crafted PDB. Microsoft also serviced supported releases in its September 8, 2026 security updates for .NET 8.0, .NET 9.0, and .NET 10.0. Additionally, if you've deployed self-contained applications targeting any of the impacted versions, these applications are also vulnerable and must be recompiled and redeployed.

Details

Module Info

• Product: .NET
• Affected packages: Microsoft.DiaSymReader.Native (in-box in the Microsoft.NETCore.App shared framework at runtimes/win/native/, not an opt-in package)
• Affected versions:
  
  • >=6.0.0 <=6.0.45
  • Microsoft.DiaSymReader.Native >=17.10.0-beta1.24272.1, <=18.9.0-beta1.26405.1
• Package manager: NuGet, Windows Installer, Docker
• GitHub repository: https://github.com/dotnet/runtime
• Published packages: Download .NET, Microsoft.DiaSymReader.Native on NuGet
• Fixed in:
  
  • NES for .NET 6.0.46

Vulnerability Info

This High-severity vulnerability is found in the native symbol reader carried by the Microsoft.NETCore.App shared framework on Windows, in versions of Microsoft.DiaSymReader.Native before 18.9.0-beta1.26405.2.

The component reads Portable PDB debug symbols on behalf of the runtime and tooling. While composing source information for a PDB, PortablePDB::ComposeSrcInfo truncated a 64-bit length value to 32 bits and then used the truncated value to size a write into a native heap allocation. A crafted Portable PDB carrying a length that wraps when narrowed produces a write past the end of that allocation. Because the write length and contents both derive from the file, this is an attacker-influenced heap corruption rather than a simple crash, which is why Microsoft scores it 8.8 with a High confidentiality, integrity, and availability impact.

CVE-2026-69439, CVE-2026-69522 and CVE-2026-71328 were reported separately and are addressed together by the single Microsoft.DiaSymReader.Native package update in NES for .NET 6.0.46.

The advisory's lower bound, 17.10.0-beta1.24272.1, is the exact version Microsoft pinned in its own final .NET 6.0 release, so the weakness is present in every .NET 6 release from that point forward and likely earlier.

Mitigation

.NET 6 is End-of-Life and will not receive any updates to address this issue. For more information see .NET and .NET Core official support policy.

Users of the affected components should apply one of the following mitigations:

• Upgrade affected applications to one of: .NET Runtime >=8.0.31, .NET Runtime >=9.0.20, .NET Runtime >=10.0.12.
• Where an application references Microsoft.DiaSymReader.Native directly, update that reference to 18.9.0-beta1.26405.2 or later.
• Leverage a commercial support partner like HeroDevs for post-EOL security support, including NES for .NET 6.0.46 or later.