CVE-2024-28121 is a high-severity (CVSS 8.8) CWE-470 vulnerability in stimulus_reflex. O3 Security confirms whether CVE-2024-28121 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Reflex arbitrary method call in stimulus_reflex
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, a proxy for how much of the ecosystem is exposed.
stimulus_reflexnpmDescription
stimulus_reflex is a system to extend the capabilities of both Rails and Stimulus by intercepting user interactions and passing them to Rails over real-time websockets. In affected versions more methods than expected can be called on reflex instances. Being able to call some of them has security implications. To invoke a reflex a websocket message of the following shape is sent: \"target\":\"[class_name]#[method_name]\",\"args\":[]. The server will proceed to instantiate reflex using the provided class_name as long as it extends StimulusReflex::Reflex. It then attempts to call method_name on the instance with the provided arguments. This is problematic as reflex.method method_name can be more methods that those explicitly specified by the developer in their reflex class. A good example is the instance_variable_set method. This vulnerability has been patched in versions 3.4.2 and 3.5.0.rc4. Users unable to upgrade should: see the backing GHSA advisory for mitigation advice.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | stimulus_reflex | ≥ 3.5.0-pre0&&< 3.5.0-rc4 | 3.5.0-rc4 |
| 📦npm | stimulus_reflex | all versions | 3.4.2 |
| 💎RubyGems | stimulus_reflex | ≥ 3.5.0.pre0&&< 3.5.0.rc4 | 3.5.0.rc4 |
| 💎RubyGems | stimulus_reflex | all versions | 3.4.2 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for stimulus_reflex. 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 stimulus_reflex to 3.5.0-rc4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2024-28121 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-2024-28121 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-2024-28121. 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-2024-28121 in your dependencies?
O3 detects CVE-2024-28121 across npm, RubyGems dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.