CVE-2026-62848: Metalama: Unsafe deserialization over Metalama's Visual Studio inter-process named pipe enables local code execution

Metalama uses a local named-pipe channel to communicate between its Visual Studio processes — the Visual Studio UI process (devenv), the out-of-process Roslyn code-analysis process, and the CodeLens process. This channel deserialized messages from the pipe without restricting which CLR types could be instantiated. A local process able to write to the pipe can send a crafted message that instantiates arbitrary .NET types — a deserialization primitive in the same class as BinaryFormatter (CWE-502), and a well-known gadget-chain code-execution vector.

The flaw is present, via two successive serializers, in every Metalama release from the first public version (2023.0) up to and including 2026.1.18, and is fixed in 2026.1.19.

The pipe name is predictable: Metalama_{role}_{processId}_{hash(PackageVersion)}, derived from the public package version and a locally-enumerable process id. This channel is used by the Visual Studio integration only (Windows named pipes); it is not used for command-line / MSBuild builds.