---
id: "CVE-2026-62847"
kind: "vulnerability"
aliases: ["CVE-2026-62847"]
title: "Metalama: predictable temp directories let local users run planted code"
severity: "high"
cvss: 8.2
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["ci", "csharp", "dotnet", "linux", "macos", "metalama", "package"]
not_affected_if: ["fixed-version", "single-user-machine", "windows-default-temp"]
published_at: "2026-10-30T21:17:13+00:00"
first_seen_at: "2026-10-30T21:25:53+00:00"
updated_at: "2026-10-30T21:26:36+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-62847", "first_seen_at": "2026-10-30T21:25:53+00:00"}]
---

# Metalama: predictable temp directories let local users run planted code

Metalama.Framework and Metalama.Tool trust compile-time DLLs in predictable temporary directories on Linux and macOS. A local unprivileged user can plant a malicious DLL that runs inside the compiler, IDE or MSBuild as a higher-privileged developer or build account.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the Metalama.Framework and Metalama.Tool package versions in the project files and lockfiles
- Check whether builds run on shared Linux or macOS machines or CI agents where other local users can write to the temp directory
- Check whether the build process uses a non-default temp location: unknown

## Fix

- Metalama.Framework and Metalama.Tool: move to `2025.1.18`, `2026.0.25` or `2026.1.19`, depending on the release line in use

## Timeline

- 2026-10-30T21:25:53+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-62847

## From the sources

Metalama is a Roslyn-based open-source patterns and architecture toolkit for C#. Prior to 2025.1.18, 2026.0.25 and 2026.1.19, Metalama.Framework and Metalama.Tool load and execute compile-time assemblies, auxiliary executable tools and embedded helper assemblies from predictable temporary directories. On `Linux` and `macOS`, the default `Path.GetTempPath()` location is world-writable, and existing artifacts are trusted based on sentinel or `.completed` marker files rather than integrity verification. A local unprivileged user on a shared machine or CI/build agent can pre-create the deterministic directory structure and plant a malicious DLL with the matching sentinel. When a higher-privileged developer or build account subsequently builds, Metalama skips regeneration and executes the planted artifact in the compiler, IDE or MSBuild process as the building user. This permits cross-user privilege escalation, reading source and secrets, supply-chain tampering with build output, or disrupting builds. Default Windows per-user temporary directories are protected by ACLs and are not affected. Deployer-selected insecure cache locations are outside the vulnerability's scope. This issue is fixed in versions 2025.1.18, 2026.0.25 and 2026.1.19.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_