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The vulnerability resides in the native component Microsoft.DiaSymReader.Native, a library responsible for parsing Portable PDB (Program Database) files that contain debugging symbol information for .NET assemblies. When processing a maliciously crafted Portable PDB, the library performs insufficient bounds checking on variable-length data streams embedded within the file format, leading to an out‑of‑bounds write into the heap. This is classified as CWE‑122 (Heap‑based Buffer Overflow). The attack vector is network‑based (AV:N) because the PDB file can be delivered via a download, email attachment, or network share. The attack complexity is low (AC:L) – no special conditions are required beyond crafting the malformed PDB. No privileges are needed (PR:N) to send the file, but user interaction (UI:R) is mandatory – the victim must open a project, compile code, or attach a debugger that loads the malicious symbols. The scope remains unchanged (S:U), as the vulnerable component does not cross security boundaries. The impact on confidentiality, integrity, and availability is high (C:H/I:H/A:H) – an attacker can read sensitive memory, execute arbitrary code, and crash the process. The CVSS base score is 8.8, rated High. The affected platforms are Windows, covering all architectures (x86, x64, ARM64). All .NET versions from 8.0 up to 11 RC1 are vulnerable when they reference affected package versions: for .NET 8, 9, and 10, the vulnerable range is Microsoft.DiaSymReader.Native >= 17.12.0‑beta1.24603.5 and <= 18.9.0‑beta1.26405.1; for .NET 11 RC1, the range is >= 17.10.0‑beta1.24272.1 and <= 18.9.0‑beta1.26405.1. The root cause stems from improper handling of the PDB’s metadata directory, where a crafted length field causes the parser to write beyond the allocated buffer during the copying of symbol records. Exploitation can be triggered by simply opening a solution or running a `dotnet` command that loads symbols, giving the attacker code execution with the privileges of the current user – which may be elevated if the user runs Visual Studio as administrator. Microsoft released version 18.9.0‑beta1.26405.2, which corrects the bounds calculations. The advisory was published on September 8, 2026, and users are strongly advised to update their package references, runtime, or Visual Studio installation immediately. Restarting all affected applications after the update is mandatory for the fix to take effect, as the native library is loaded into memory at process startup. No workarounds other than updating are provided, underscoring the criticality of applying the patch.
DailyCVE Form:
Platform: Windows .NET 8-11
Version: Specific package versions
Vulnerability: Heap-based Buffer Overflow
Severity: High CVSS 8.8
date: September 8 2026
Prediction: Patched version available
What Undercode Say:
Detect vulnerable package references in all .csproj files
find . -name ".csproj" -exec grep -H "Microsoft.DiaSymReader.Native" {} \;
Check for known vulnerable versions using dotnet CLI
dotnet list package --vulnerable --include-transitive
Show detailed package info including versions
dotnet list package --outdated --include-transitive | grep -A 5 DiaSymReader
Update the package to the patched version in a specific project
dotnet add package Microsoft.DiaSymReader.Native -v 18.9.0-beta1.26405.2
Verify current .NET SDK and runtime versions
dotnet --info
To force a full clean and rebuild after update
dotnet clean && dotnet build --no-incremental
Exploit: (Educational Purposes!)
An attacker creates a Portable PDB file where the stream directory advertises a large data length for a particular table, but the actual payload contains more bytes than the allocated heap chunk. When the native parser reads the table, it copies the oversized data into the fixed‑size buffer, overwriting adjacent heap metadata and function pointers. By carefully crafting the overwritten data, the attacker redirects execution flow to shellcode embedded elsewhere in the PDB. The malicious PDB is then distributed via a phishing link or placed in a project’s output folder. When a developer opens the project in Visual Studio or runs dotnet run, the debugging symbols are loaded, triggering the overflow and spawning a reverse shell with the developer’s privileges.
Protection: from this CVE
- Immediately update the Microsoft.DiaSymReader.Native package to version 18.9.0‑beta1.26405.2 or later in all projects.
- Install the latest .NET SDK and Visual Studio updates released after September 8, 2026.
- Restart all running .NET applications and Visual Studio instances to unload the vulnerable native DLL.
- For CI/CD pipelines, ensure the patched version is enforced via Directory.Packages.props or NuGet locking.
- Block untrusted PDB files from being downloaded or opened until the patch is applied.
Impact:
Successful exploitation grants an unauthenticated attacker the ability to execute arbitrary code with elevated privileges on the target Windows machine. This can lead to full system compromise, including data theft, installation of malware, or lateral movement within an enterprise network. Development environments and build servers are particularly at risk because they often run with administrative rights and handle numerous external symbols, making them prime targets for supply‑chain attacks. The high CVSS score (8.8) reflects the severe consequences, although user interaction is required to trigger the malicious parse.
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Sources:
Reported By: github.com
Extra Source Hub:
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