Deserialization in Ruby Erb

CVE-2026-41316

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 · last modified .

CVSS v3 metric

CVSS v3 base score 8.1 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.013 (69.4th percentile), scored .

Low probability of exploitation in the next 30 days, but still tracked. 69th percentile — 69.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-41316: held from 0.011 to 0.013.

EPSS over last 30 days · oldest: 0.011 · newest: 0.013 · change: +0.002

Affected products

  • Ruby Erb — versions < 4.0.3.1, = 4.0.4, >= 5.0.0, < 6.0.1.1

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-41316?
CVE-2026-41316 is a high-severity vulnerability in Ruby Erb, classified under Protection Mechanism Failure. CVSS score: 8.1/10. Published 2026-04-24.
How severe is CVE-2026-41316?
High severity. CVSS v3 base score is 8.1 out of 10.