How severe is CVE-2025-43855?

No CVSS score has been assigned to CVE-2025-43855 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2025-43855?

CVE-2025-43855 affects the following packages: @trpc/server (npm). Ecosystems affected: npm.

How do I fix CVE-2025-43855?

Update @trpc/server to 11.1.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-43855 is resolved across your whole dependency graph.

How do I detect CVE-2025-43855 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @trpc/server. 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.

How do I mitigate CVE-2025-43855 if there is no patch (or I can't update yet)?

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 does O3 Security protect against CVE-2025-43855?

O3 pinpoints whether CVE-2025-43855 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Is CVE-2025-43855 actively exploited in the wild?

No public exploit code has been indexed for CVE-2025-43855 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2025-43855?

CVE-2025-43855 has an EPSS (Exploit Prediction Scoring System) score of 0.3%, placing it in the 27th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2025-43855?

CVE-2025-43855 is classified as CWE-248 (CWE-248). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2025-43855 published, and has it been updated?

CVE-2025-43855 was published on April 24, 2025 and was last updated on April 2, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

CVE-2025-43855: tRPC 11 WebSocket DoS Vulnerability

EPSS Exploitation Probability

via FIRST.org ↗

0.3%probability of exploitation in next 30 days

Lower Risk27th percentile+0.06%

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

1 pkg affected

📦@trpc/server

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects npm packages — download data is not available via public APIs for these ecosystems.

Description

tRPC allows users to build & consume fully typesafe APIs without schemas or code generation. In versions starting from 11.0.0 to before 11.1.1, an unhandled error is thrown when validating invalid connectionParams which crashes a tRPC WebSocket server. This allows any unauthenticated user to crash a tRPC 11 WebSocket server. Any tRPC 11 server with WebSocket enabled with a createContext method set is vulnerable. This issue has been patched in version 11.1.1.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`@trpc/server`	≥ 11.0.0&&< 11.1.1	11.1.1

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @trpc/server. 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 @trpc/server to 11.1.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-43855 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-2025-43855 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-2025-43855. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

tRPC allows users to build & consume fully typesafe APIs without schemas or code generation. In versions starting from 11.0.0 to before 11.1.1, an unhandled error is thrown when validating invalid connectionParams which crashes a tRPC WebSocket server. This allows any unauthenticated user to crash a tRPC 11 WebSocket server. Any tRPC 11 server with WebSocket enabled with a createContext method set is vulnerable. This issue has been patched in version 11.1.1.

O3 Security · Impact-Aware SCA

Is CVE-2025-43855 in your dependencies?

O3 detects CVE-2025-43855 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

Scan my dependencies How O3 SCA works

CVE-2025-43855