Answer in brief
CVE-2026-9595 records a Medium severity (CVSS 5.3) vulnerability in webpack-dev-server vulnerable to HMR WebSocket interception via permissive user proxies. The current sources do not mark it as known exploited. The current feed maps webpack-dev-server (npm), webpack-dev-server (npm). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 5.3. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps webpack-dev-server (npm), webpack-dev-server (npm). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| webpack-dev-servernpm | <5.2.5 | 5.2.5 |
| webpack-dev-servernpm | >=0 <5.2.5 | 5.2.5 |
Published upstream
Jun 17, 2026
Evidence: source:osv:source_dates:source-dates:recordSource modified
Sep 10, 2026
Evidence: source:osv:source_dates:source-dates:recordFirst seen by HOL
Jun 19, 2026
### Impact When a user-configured proxy on `webpack-dev-server` has a broad context (e.g. `/`) and `ws: true`, it also intercepts the dev server's own HMR WebSocket and forwards it to the proxy target. This leaks the browser's cookies and `Origin` header to the backend, bypasses the dev server's Host/Origin validation, and corrupts the HMR socket (both HMR and the proxy end up writing to the same socket). ### Patches Fixed in `webpack-dev-server` 5.2.5. ### Workarounds Scope user-defined proxy `context` to specific paths instead of `/`, or omit `ws: true` from the proxy entry when WebSocket forwarding is not required.
Quoted source text, attributed separately from HOL analysis.