mediumCVSS 5.3Vulnerability
CVE-2026-9595
### 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.
Properties
- severity
- medium
- summary
- webpack-dev-server vulnerable to HMR WebSocket interception via permissive user proxies
- epss_score
- 0.00163
- cvss_score
- 5.3
- ghsa_published
- 2026-06-17T18:13:31Z
- source_url
- https://github.com/advisories/GHSA-mx8g-39q3-5c79
- ghsa_updated
- 2026-06-17T18:13:33Z
- ghsa_id
- GHSA-mx8g-39q3-5c79
- cve_id
- CVE-2026-9595
- cvss_vector
- CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
- signal_observed_at
- 2026-09-11T17:55:57+00:00
- is_ghsa_only
- false
- epss_percentile
- 0.05843
Related Entities (6)
ENRICHED_BY (1)
→[Source]FIRST EPSS
REPORTED_BY (1)
→[Source]GitHub Advisory Database
VULNERABLE_TO (1)
←[Software]npm/webpack-dev-server
AFFECTS (1)
→[Software]npm/webpack-dev-server
HAS_WEAKNESS (2)
→[Weakness]Origin Validation Error
→[Weakness]Unintended Proxy or Intermediary ('Confused Deputy')
Explore deeper with Ninja Signal's threat intelligence graph