ERB has an @_init deserialization guard bypass via def_module / def_method / def_class_CVE-2026-41316

{
    "lastseen": "",
    "description": "ERB is a templating system for Ruby. Ruby 2.7.0 (before ERB 2.2.0 was published on rubygems.org) introduced an `@_init` instance variable guard in `ERB#result` and `ERB#run` to prevent code execution when an ERB object is reconstructed via `Marshal.load` (deserialization). However, three other public methods that also evaluate `@src` via `eval()` were not given the same guard: `ERB#def_method`, `ERB#def_module`, and `ERB#def_class`. An attacker who can trigger `Marshal.load` on untrusted data in a Ruby application that has `erb` loaded can use `ERB#def_module` (zero-arg, default parameters) as a code execution sink, bypassing the `@_init` protection entirely. ERB 4.0.3.1, 4.0.4.1, 6.0.1.1, and 6.0.4 patch the issue.",
    "published": "2026-04-24T02:35:41.160Z",
    "modified": "2026-04-24T02:35:41.160Z",
    "type": "cve",
    "title": "ERB has an @_init deserialization guard bypass via def_module / def_method / def_class",
    "source": "GitHub_M",
    "references": "https://github.com/ruby/erb/security/advisories/GHSA-q339-8rmv-2mhv",
    "id": "CVE-2026-41316",
    "bulletinFamily": "",
    "cwe": [
        "CWE-693"
    ],
    "cvelist": null,
    "sourceData": "ruby erb < 4.0.3.1\nruby erb = 4.0.4\nruby erb >= 5.0.0, < 6.0.1.1\nruby erb >= 6.0.2, < 6.0.4",
    "sourceHref": "",
    "cvss": {
        "score": 8.1,
        "severity": "HIGH",
        "vector": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H",
        "version": "3.1"
    },
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        "confidentialityImpact": "",
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        "cvssV3": {
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    },
    "href": "",
    "category_name": "CVE",
    "post_link": "",
    "product": "erb",
    "version": "< 4.0.3.1",
    "vendor": "ruby",
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}