CVE-2026-62847: Metalama.Framework Metalama Allows Local Code Execution Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-m6wq-39m7-9xpp",
  "modified" : "2026-10-14T19:24:53Z",
  "published" : "2026-10-14T19:24:53Z",
  "aliases" : [ "CVE-2026-62847" ],
  "summary" : "Metalama allows local code execution through DLL planting in shared temporary directories",
  "details" : "## Summary\n\nMetalama 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.\n\nA 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.\n\nAffected load-and-execute paths:\n- the cache of compile-time assemblies that Metalama generates from your aspects;\n- auxiliary executable tools that Metalama extracts to a local directory and then launches;\n- embedded .NET helper assemblies that Metalama extracts to a local directory and loads into the build / IDE process.\n\n## Impact\n\nArbitrary 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.\n\n## Affected configurations\n\n- **Linux and macOS, default configuration — affected.** The shipped default uses the world-writable system temp directory.\n- **Windows, default configuration — not affected.** The default per-user temporary directory is protected by OS ACLs, so cross-user planting is not possible.\n- 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.\n\n## Severity\n\nCVSS 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).\n\nCVSS 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.\n\n## Fix\n\nCaches 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**.\n\n## Weaknesses\n\n- CWE-377: Insecure Temporary File\n- CWE-427: Uncontrolled Search Path Element\n\n## Affected packages\n\n- Metalama.Framework < 2026.1.19, \n- Metalama.Tool < 2026.1.19\n\nInternal tracking: metalama/Metalama#1650.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H"
  }, {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "NuGet",
      "name" : "Metalama.Framework"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2026.1.0-preview"
      }, {
        "fixed" : "2026.1.19"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "NuGet",
      "name" : "Metalama.Tool"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2026.1.0-preview"
      }, {
        "fixed" : "2026.1.19"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "NuGet",
      "name" : "Metalama.Framework"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2025.1.18"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "NuGet",
      "name" : "Metalama.Tool"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "2025.1.18"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "NuGet",
      "name" : "Metalama.Tool"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2026.0.0-preview"
      }, {
        "fixed" : "2026.0.25"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "NuGet",
      "name" : "Metalama.Framework"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2026.0.0-preview"
      }, {
        "fixed" : "2026.0.25"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/metalama/Metalama/security/advisories/GHSA-m6wq-39m7-9xpp"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/metalama/Metalama/pull/1719"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/metalama/Metalama/commit/09911349a916e82194b1cfaa6d0a38acad928fc9"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/metalama/Metalama/commit/92c4feecfce86d18fcb007ab6d3a1b4383326a2e"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/metalama/Metalama/commit/ab9407263203c66d7c5680a34c28dba31f9951c9"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/metalama/Metalama"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-377", "CWE-427" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-10-14T19:24:53Z",
    "nvd_published_at" : null
  }
}