PostSharp Metalama: Unsafe deserialization in Visual Studio named pipes (CVE-2026-62848)

Metalama's Visual Studio integration utilizes inter-process communication (IPC) via local Windows named pipes to exchange data between the Visual Studio UI process (devenv), Roslyn analysis processes, and CodeLens. These pipes perform unsafe deserialization of incoming messages without an allow-list, enabling arbitrary .NET type instantiation.

The vulnerability manifests through two primary deserialization mechanisms:

1. Newtonsoft.Json with TypeNameHandling.All (Metalama 2023.0 through 2026.0.x).
2. Typeless MessagePack (Metalama 2026.1.0 through 2026.1.18).

Both mechanisms leverage predictable pipe names (Metalama_{role}_{processId}_{hash(PackageVersion)}). Because the pipe access is restricted to the same logged-in user via default Windows ACLs, successful exploitation allows an attacker already executing code under the developer's context to achieve code execution within the Visual Studio process.

Impact

Successful exploitation results in arbitrary code execution within the Visual Studio UI, Roslyn analysis, or CodeLens processes. This grants the attacker full control over the process context, including the ability to access data and modify developer environment states, limited to the permissions of the current logged-in user.

Recommendation

• Upgrade Metalama.Framework to version 2026.1.19 or later.
• Update the PostSharpTechnologies.PostSharp Visual Studio extension to version 2026.1.5 or later.
• Uninstall retired extensions PostSharpTechnologies.Metalama and PostSharpTechnologies.caravela and migrate to the maintained PostSharp extension (>= 2026.1.5).
• Prioritize these updates for developer workstations where the Metalama extension is active.