CVE-2026-41316
HIGHCVE-2026-41316 is a high-severity (CVSS 8.1) CWE-693 vulnerability in erb. O3 Security confirms whether CVE-2026-41316 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
ERB has an @_init deserialization guard bypass via def_module / def_method / def_class
Blast Radius
erb💎erb💎erb💎erbReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | erb | all versions | 4.0.3.1 |
| 💎RubyGems | erb | ≥ 4.0.4&&< 4.0.4.1 | 4.0.4.1 |
| 💎RubyGems | erb | ≥ 5.0.0&&< 6.0.1.1 | 6.0.1.1 |
| 💎RubyGems | erb | ≥ 6.0.2&&< 6.0.4 | 6.0.4 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for erb. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update erb to 4.0.3.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-41316 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-41316 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-41316. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-41316 in your dependencies?
O3 detects CVE-2026-41316 across RubyGems dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.