---
id: CVE-2026-62847
aliases:
  - GHSA-m6wq-39m7-9xpp
title: >-
  Metalama allows local code execution through DLL planting in shared temporary
  directories
summary: >-
  Metalama allows local code execution through DLL planting in shared temporary
  directories
severity: medium
cvss: 8.2
cwe:
  - CWE-377
  - CWE-427
vendor: Metalama
product: Metalama.Framework
ecosystem: nuget
affected:
  - 'Metalama.Framework >= 2026.1.0-preview, < 2026.1.19'
  - 'Metalama.Tool >= 2026.1.0-preview, < 2026.1.19'
  - Metalama.Framework < 2025.1.18
  - Metalama.Tool < 2025.1.18
  - 'Metalama.Tool >= 2026.0.0-preview, < 2026.0.25'
  - 'Metalama.Framework >= 2026.0.0-preview, < 2026.0.25'
patched:
  - Metalama.Framework 2026.1.19
  - Metalama.Tool 2026.1.19
  - Metalama.Framework 2025.1.18
  - Metalama.Tool 2025.1.18
  - Metalama.Tool 2026.0.25
  - Metalama.Framework 2026.0.25
published: '2026-10-14'
updated: '2026-10-14'
sourceUpdated: '2026-10-14T19:24:55Z'
source: GHSA
sourceUrl: 'https://github.com/advisories/GHSA-m6wq-39m7-9xpp'
references:
  - url: >-
      https://github.com/metalama/Metalama/security/advisories/GHSA-m6wq-39m7-9xpp
  - url: 'https://github.com/metalama/Metalama/pull/1719'
  - url: >-
      https://github.com/metalama/Metalama/commit/09911349a916e82194b1cfaa6d0a38acad928fc9
  - url: >-
      https://github.com/metalama/Metalama/commit/92c4feecfce86d18fcb007ab6d3a1b4383326a2e
  - url: >-
      https://github.com/metalama/Metalama/commit/ab9407263203c66d7c5680a34c28dba31f9951c9
  - url: 'https://github.com/advisories/GHSA-m6wq-39m7-9xpp'
tags:
  - ghsa
  - nuget
ingestedAt: '2026-10-14T19:49:57.617Z'
---

## Overview

## Summary

Metalama loaded and executed compile-time assemblies, auxiliary executable tools, and embedded helper assemblies from predictable temporary directories. On Linux and macOS the default cache location was the world-writable system temporary directory (`Path.GetTempPath()`, i.e. `/tmp`), and previously-generated artifacts were trusted based on the presence of a sentinel/`.completed` marker file rather than on any integrity verification.

A local, unprivileged user on a shared machine or CI/build agent can pre-create the deterministic cache directory structure and plant a malicious DLL together with the matching sentinel file. When a higher-privileged user (or build/service account) subsequently runs a build, Metalama finds the sentinel, skips regeneration, and loads and executes the attacker-supplied assembly inside the compiler / IDE / MSBuild process.

Affected load-and-execute paths:
- the cache of compile-time assemblies that Metalama generates from your aspects;
- auxiliary executable tools that Metalama extracts to a local directory and then launches;
- embedded .NET helper assemblies that Metalama extracts to a local directory and loads into the build / IDE process.

## Impact

Arbitrary code execution in the security context of the building user — i.e. a local privilege escalation across user accounts on shared POSIX systems (multi-user developer machines, CI/build agents). The attacker obtains code execution as the victim without holding the victim's privileges, and can read source/secrets, tamper with build output (supply-chain injection), or disrupt builds.

## Affected configurations

- **Linux and macOS, default configuration — affected.** The shipped default uses the world-writable system temp directory.
- **Windows, default configuration — not affected.** The default per-user temporary directory is protected by OS ACLs, so cross-user planting is not possible.
- The `METALAMA_TEMP` environment variable is a deployer-controlled override and is **out of scope**: pointing it at an insecure (e.g. world-writable or attacker-owned) location is a deployment misconfiguration, not a defect in the product.

## Severity

CVSS v3.1: `AV:L/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H` = **8.2 (High)** for the affected POSIX default configuration (Scope:Changed reflects the cross-user privilege escalation).

CVSS v4.0 cross-check: `CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:P/VC:L/VI:H/VA:L/SC:L/SI:H/SA:H` = 6.0 (Medium), which more granularly attributes low impact to the cache itself and high impact to the subsequent build process. The honest range is therefore Medium-High depending on the scoring model and platform.

## Fix

Caches and extraction directories were relocated from the world-writable system temp directory to per-user application-data locations (`$XDG_CACHE_HOME` / `~/.cache/Metalama` on POSIX), relying on OS-enforced per-user ownership as the trust boundary. Fixed in **2026.1.19**.

## Weaknesses

- CWE-377: Insecure Temporary File
- CWE-427: Uncontrolled Search Path Element

## Affected packages

- Metalama.Framework < 2026.1.19, 
- Metalama.Tool < 2026.1.19

Internal tracking: metalama/Metalama#1650.

## Affected packages

- `Metalama.Framework >= 2026.1.0-preview, < 2026.1.19`
- `Metalama.Tool >= 2026.1.0-preview, < 2026.1.19`
- `Metalama.Framework < 2025.1.18`
- `Metalama.Tool < 2025.1.18`
- `Metalama.Tool >= 2026.0.0-preview, < 2026.0.25`
- `Metalama.Framework >= 2026.0.0-preview, < 2026.0.25`

## Remediation

Upgrade to a patched release:

- `Metalama.Framework 2026.1.19`
- `Metalama.Tool 2026.1.19`
- `Metalama.Framework 2025.1.18`
- `Metalama.Tool 2025.1.18`
- `Metalama.Tool 2026.0.25`
- `Metalama.Framework 2026.0.25`