CVE-2026-9595
webpack-dev-server vulnerable to HMR WebSocket interception via permissive user proxies
- 5.3MediumCVSS base score
- 0.16%Exploitation in 30 daysEPSS · top 94% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
Description
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 [email protected]. 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.
Timeline
ID reserved
By openjs
- 20 days later
· 20 days later
Published
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| openjsCNA (assigner) | 3.1 | Medium5.3 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L |
| NVDNVD · Analyzed | 3.1 | Medium4.3 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L |
- EPSS (exploitation in 30 days)
- 0.16% · top 94% of all CVEs (11 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: yes · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 5.3.
Affected products
webpack-dev-server · webpack-dev-server
- affected < 5.2.5
- unaffected 5.2.5
Affected packages
From reviewed advisories of the GitHub Advisory Database.
- npmwebpack-dev-serverGHSA-mx8g-39q3-5c79 (opens in a new tab)
References
References5
- https://github.com/webpack/webpack-dev-server/security/advisories/GHSA-mx8g-39q3-5c79 (opens in a new tab)
- https://cna.openjsf.org/security-advisories.html (opens in a new tab)
- https://github.com/webpack/webpack-dev-server/pull/4316 (opens in a new tab)
- https://github.com/vuejs/vue-cli/commit/72ba7505aff2a8314e82aa5082379a77504a1fcb (opens in a new tab)
- https://github.com/facebook/create-react-app/pull/7444 (opens in a new tab)
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2026-36729 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisory GHSA-mx8g-39q3-5c79 (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2026-9595)Record last updated .