CVE-2026-42190 — rwsdk
MEDIUMCVE-2026-42190 is a medium-severity (CVSS 5.3) Cross-Site Request Forgery (CSRF) vulnerability in rwsdk. A fix is available for rwsdk — see the affected versions and patch details below.
RedwoodSDK: Same-site CSRF in in server actions
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-42190.
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.
How urgent is this, really
CVE-2026-42190 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,567 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
rwsdknpmDescription
Summary
Server actions in rwsdk apply HTTP method enforcement but no origin validation. A request originating from a different origin that the browser treats as same-site can invoke a server action with the victim's session cookie attached.
Impact
An attacker who controls any origin the browser considers same-site with the deployed app can induce an authenticated victim's browser to invoke arbitrary server actions. The exposure depends on deployment shape:
- Apps deployed on custom domains (for example
app.example.com) are exposed whenever the attacker controls any sibling subdomain under the same registrable domain. Plausible vectors include subdomain takeover of stale DNS records pointing at third-party services, cross-site scripting on a sibling application, or content served from a user-content subdomain. - Apps deployed on platform-suffix domains on the Public Suffix List (
*.workers.dev,*.pages.dev) are not exposed to the sibling-subdomain vector, because sibling subdomains under those suffixes are treated as cross-site. - In local development,
localhoston any other port is treated as same-site with the app's dev server. A separate process running on the developer's machine can invoke server actions against the dev server.
The attacker cannot read action responses (mode: "no-cors" yields opaque responses). Impact is therefore limited to side effects of action invocation: writes, state changes, and any externally observable action the application performs in response.
Cross-site requests from unrelated origins (evil.com targeting app.com) are not affected because SameSite=Lax session cookies are not attached by default in that scenario.
Affected Configurations
Applications using rwsdk server actions (serverAction() or functions invoked via the RSC action protocol) in combination with cookie-based authentication. serverQuery() is not affected because it is designed to be idempotent and is invoked via GET.
Patch
The patched release enforces an Origin/Host match for non-GET action requests. Requests whose Origin header does not match the request's own origin are rejected with HTTP 403 unless the origin is listed in a new allowedOrigins configuration option.
No application code changes are required for apps that invoke server actions from their own origin. Apps that legitimately invoke server actions from another origin must add those origins to the allowedOrigins option on defineApp.
Credits
Reported by @mthx.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | rwsdk | ≥ 1.0.0-beta.50&&< 1.2.3 | 1.2.3npm install rwsdk@1.2.3 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for rwsdk, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update rwsdk to 1.2.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-42190 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 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-42190 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-42190. 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-2026-42190 in your dependencies?
O3 Security finds CVE-2026-42190 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.