CVE-2024-28121
HIGHReflex arbitrary method call in stimulus_reflex
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
stimulus_reflex📦stimulus_reflex💎stimulus_reflex💎stimulus_reflexReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects npm, RubyGems packages — download data is not available via public APIs for these ecosystems.
Description
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.