CVE-2026-34077 is a high-severity (CVSS 7.5) CWE-770 vulnerability in react-router. A fix is available for react-router — see the affected versions and patch details below.
React Router vulnerable to Denial of Service via reflected user input in single-fetch
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- 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-2026-34077.
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-2026-34077 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 379,145 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.
react-routernpmturbo-streamnpmDescription
A DoS vulnerability exists in the React Router v7 Framework Mode, as well as Remix v2.9.0+ with Single Fetch enabled. In some scenarios the underlying serialization algorithm can become a bottleneck when encoding specific types of data into server responses. Please upgrade to React Router v7.14.0 or later.
[!NOTE] This does not impact your React Router application if you are using Declarative Mode (
<BrowserRouter>) or Data Mode (createBrowserRouter/<RouterProvider>).
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | react-router | ≥ 7.0.0&&< 7.14.0 | 7.14.0npm install react-router@7.14.0 |
| 📦npm | turbo-stream | all versions | 3.0.0npm install turbo-stream@3.0.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for react-router, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update react-router to 7.14.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-34077 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-34077 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-34077. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
React Router is vulnerable to client-side XSS in unstable RSC redirect handling when redirects come from untrusted sources. A remote unauthenticated attacker who can cause a victim to follow a crafted redirect (user interaction required) may execute script in the browser context, leading to denial of service. Only…
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Data Grid 8.6.2 | react-router | RHSA-2026:41951 |
Frequently Asked Questions
Is CVE-2026-34077 in your dependencies?
O3 Security finds CVE-2026-34077 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.