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

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.

Timeline

  1. ID reserved

    By GitHub_M

  2. · 4 days later

    Published

  3. · 4 months later

    Record updated

Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.

Scores

CVSS scores of CVE-2026-41316, by who scored it
Scored byCVSSScoreVector
GitHub_MCNA (assigner)3.1High8.1CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
redhat-SADPADP (enrichment)3.1High8.1CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
NVDNVD · Deferred3.1High8.1CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS (exploitation in 30 days)
1.1% · top 33% of all CVEs (12 Nov 2026)
CISA SSVC
Exploitation: none · Automatable: no · Technical impact: total
Loading the EPSS history…

The list uses the assigner's score when there is one, then CISA's, then NVD's: High 8.1.

Affected products

  • ruby · erb

    • affected < 4.0.3.1
    • affected = 4.0.4
    • affected >= 5.0.0, < 6.0.1.1
    • affected >= 6.0.2, < 6.0.4

Affected packages

From reviewed advisories of the GitHub Advisory Database.

References

References17

Sources

The same CVE in the primary databases and aggregators, to check against.

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Record last updated .