webpack-dev-server vulnerable to HMR WebSocket interception via permissive user proxies

MITRE NVD CVE.ORG JSON API Print: PDF PDF

Summary

CVECVE-2026-9595
StatePUBLISHED
Assigneropenjs
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-06-15 16:16:35 UTC
Updated2026-06-16 17:24:37 UTC
DescriptionImpact: 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.

Risk And Classification

Primary CVSS: v3.1 4.3 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

EPSS: 0.001630000 probability, percentile 0.057790000 (date 2026-06-23)

Problem Types: CWE-346 | CWE-441 | CWE-346 CWE-346: Origin Validation Error | CWE-441 CWE-441: Unintended Proxy or Intermediary ('Confused Deputy')

VersionSourceTypeScoreSeverityVector
3.1[email protected]Primary4.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
3.1ce714d77-add3-4f53-aff5-83d477b104bbSecondary5.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
3.1CNACVSS5.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Webpack.js Webpack-dev-server All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Webpack-dev-server Webpack-dev-server affected 5.2.5 semver Not specified
CNA Webpack-dev-server Webpack-dev-server unaffected 5.2.5 semver Not specified

References

ReferenceSourceLinkTags
cna.openjsf.org/security-advisories.html ce714d77-add3-4f53-aff5-83d477b104bb cna.openjsf.org Vendor Advisory
github.com/webpack/webpack-dev-server/security/advisories/GHSA-mx8g-39q3... ce714d77-add3-4f53-aff5-83d477b104bb github.com Mitigation, Vendor Advisory
github.com/facebook/create-react-app/pull/7444 ce714d77-add3-4f53-aff5-83d477b104bb github.com Issue Tracking, Patch
github.com/webpack/webpack-dev-server/pull/4316 ce714d77-add3-4f53-aff5-83d477b104bb github.com Issue Tracking, Patch
github.com/vuejs/vue-cli/commit/72ba7505aff2a8314e82aa5082379a77504a1fcb ce714d77-add3-4f53-aff5-83d477b104bb github.com Patch
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: bjohansebas (en)

CNA: UlisesGascon (en)

CNA: ajhyndman (en)

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