GHSA-M6WQ-39M7-9XPP
Vulnerability from github – Published: 2026-10-14 19:24 – Updated: 2026-10-14 19:24Summary
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_TEMPenvironment 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": [
{
"package": {
"ecosystem": "NuGet",
"name": "Metalama.Framework"
},
"ranges": [
{
"events": [
{
"introduced": "2026.1.0-preview"
},
{
"fixed": "2026.1.19"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "NuGet",
"name": "Metalama.Tool"
},
"ranges": [
{
"events": [
{
"introduced": "2026.1.0-preview"
},
{
"fixed": "2026.1.19"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "NuGet",
"name": "Metalama.Framework"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "2025.1.18"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "NuGet",
"name": "Metalama.Tool"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "2025.1.18"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "NuGet",
"name": "Metalama.Tool"
},
"ranges": [
{
"events": [
{
"introduced": "2026.0.0-preview"
},
{
"fixed": "2026.0.25"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "NuGet",
"name": "Metalama.Framework"
},
"ranges": [
{
"events": [
{
"introduced": "2026.0.0-preview"
},
{
"fixed": "2026.0.25"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-62847"
],
"database_specific": {
"cwe_ids": [
"CWE-377",
"CWE-427"
],
"github_reviewed": true,
"github_reviewed_at": "2026-10-14T19:24:53Z",
"nvd_published_at": null,
"severity": "MODERATE"
},
"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 \u2014 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\u0027s 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 \u2014 affected.** The shipped default uses the world-writable system temp directory.\n- **Windows, default configuration \u2014 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 \u003c 2026.1.19, \n- Metalama.Tool \u003c 2026.1.19\n\nInternal tracking: metalama/Metalama#1650.",
"id": "GHSA-m6wq-39m7-9xpp",
"modified": "2026-10-14T19:24:53Z",
"published": "2026-10-14T19:24:53Z",
"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"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H",
"type": "CVSS_V3"
},
{
"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",
"type": "CVSS_V4"
}
],
"summary": "Metalama allows local code execution through DLL planting in shared temporary directories"
}
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