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Vulnerability details

CVE-2026-41316

ruby erb

ERB has an @_init deserialization guard bypass via def_module / def_method / def_class

CVSS 3.1
8.1High

Official 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.

CVSS scores

ScoreVersionSourceVector
8.1High 3.1 CVEProject cvelistV5 (CNA) (GitHub_M) CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
8.1High 3.1 CVEProject cvelistV5 (CNA) (redhat-SADP) CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

VendorProductVersionsSource
ruby erb < 4.0.3.1 CVEProject cvelistV5 (CNA)
ruby erb = 4.0.4 CVEProject cvelistV5 (CNA)
ruby erb >= 5.0.0, < 6.0.1.1 CVEProject cvelistV5 (CNA)
ruby erb >= 6.0.2, < 6.0.4 CVEProject cvelistV5 (CNA)

References and advisories

17
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Details

Published
2026-04-24
Last updated
2026-08-24
State
Published
Assigner (CNA)
GitHub_M

Exploit prediction (EPSS)

1.13%
Probability of exploitation in 30 days
66.5%
Percentile (among all CVEs)

SSVC assessment (CISA)

Automatable
No
Exploitation
None
Technical impact
Total

Weaknesses (CWE)

  • CWE-693
    Protection Mechanism Failure
  • CWE-502
    Deserialization of Untrusted Data