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High, CVSS 8.7amended

tRPC 11 WebSocket DoS Vulnerability

CVE-2025-43855GHSA-pj3v-9cm8-gvj8

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (@trpc/server 11.1.1), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
8.7 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N · score source
EPSS
  • CVE-2025-43855: 0.42% estimated exploitation activity in the next 30 days; percentile 36.65 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary 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. Details Any tRPC 11 server with WebSocket enabled with a createContext method set is vulnerable. Here is an example: https://github.com/user-attachments/assets/ce1b2d32-6103-4e54-8446-51535b293b05 I have a working reproduction here if you would like to test: https://github.com/lukechilds/trpc-vuln-reproduction The connectionParams logic introduced in https://github.com/trpc/trpc/pull/5839 does not safely handle invalid connectionParams objects. During validation if the object does not match an expected shape an error will be thrown: https://github.com/trpc/trpc/blob/8cef54eaf95d8abc8484fe1d454b6620eeb57f2f/packages/server/src/unstable-core-do-not-import/http/parseConnectionParams.ts#L27-L33 This is called during WebSocket connection setup inside createCtxPromise() here:…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-pj3v-9cm8-gvj8

  2. Revision 2 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  3. Revision 1 · created ·

    Published from osv record GHSA-pj3v-9cm8-gvj8

Agent brief

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# Patch Next advisory brief: CVE-2025-43855

Advisory: tRPC 11 WebSocket DoS Vulnerability
IDs: CVE-2025-43855, GHSA-pj3v-9cm8-gvj8
Record: https://patchnext.com/advisories/cve-2025-43855 (revision 3, source checked 26 Oct 2026, 12:37 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @trpc/server 11.1.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @trpc/server: affected >= 11.0.0, < 11.1.1; fixed in 11.1.1

## Suggested inspection (read-only)
- `npm ls @trpc/server --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on @trpc/server.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-pj3v-9cm8-gvj8 (OSV record GHSA-pj3v-9cm8-gvj8 lists affected ranges: npm @trpc/server >=11.0.0 <11.1.1 (fixed))
- Verified: https://github.com/advisories/GHSA-pj3v-9cm8-gvj8 (GitHub-reviewed advisory GHSA-pj3v-9cm8-gvj8 lists affected ranges: npm @trpc/server >=11.0.0 <11.1.1)

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