Vulnerability-Lookup

GHSA-MX8G-39Q3-5C79

Vulnerability from github – Published: 2026-06-17 18:13 – Updated: 2026-06-17 18:13

Summary

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

Details

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.

Severity

5.3 (Medium)


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

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JSON

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{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "webpack-dev-server"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "5.2.5"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-9595"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-346",
      "CWE-441"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-17T18:13:31Z",
    "nvd_published_at": "2026-06-15T16:16:35Z",
    "severity": "MODERATE"
  },
  "details": "### Impact\n\nWhen a user-configured proxy on `webpack-dev-server` has a broad context (e.g. `/`) and `ws: true`, it also intercepts the dev server\u0027s own HMR WebSocket and forwards it to the proxy target. This leaks the browser\u0027s cookies and `Origin` header to the backend, bypasses the dev server\u0027s Host/Origin validation, and corrupts the HMR socket (both HMR and the proxy end up writing to the same socket).\n\n### Patches\n\nFixed in `webpack-dev-server` 5.2.5.\n\n### Workarounds\n\nScope user-defined proxy `context` to specific paths instead of `/`, or omit `ws: true` from the proxy entry when WebSocket forwarding is not required.",
  "id": "GHSA-mx8g-39q3-5c79",
  "modified": "2026-06-17T18:13:32Z",
  "published": "2026-06-17T18:13:31Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/webpack/webpack-dev-server/security/advisories/GHSA-mx8g-39q3-5c79"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-9595"
    },
    {
      "type": "WEB",
      "url": "https://github.com/facebook/create-react-app/pull/7444"
    },
    {
      "type": "WEB",
      "url": "https://github.com/webpack/webpack-dev-server/pull/4316"
    },
    {
      "type": "WEB",
      "url": "https://github.com/vuejs/vue-cli/commit/72ba7505aff2a8314e82aa5082379a77504a1fcb"
    },
    {
      "type": "WEB",
      "url": "https://cna.openjsf.org/security-advisories.html"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/webpack/webpack-dev-server"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "webpack-dev-server vulnerable to HMR WebSocket interception via permissive user proxies"
}

CVE-2026-9595 (GCVE-0-2026-9595)

Vulnerability from cvelistv5 – Published: 2026-06-15 15:00 – Updated: 2026-06-15 16:08

Title

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

Summary

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.

Severity

5.3 (Medium)


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

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-06-15 16:08 UTC

CWE

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

Assigner

openjs redhat root

References

5 references

URL	Tags
https://github.com/webpack/webpack-dev-server/sec…
https://cna.openjsf.org/security-advisories.html
https://github.com/webpack/webpack-dev-server/pull/4316
https://github.com/vuejs/vue-cli/commit/72ba7505a…
https://github.com/facebook/create-react-app/pull/7444

Impacted products

1 product

Vendor	Product	Version
webpack-dev-server	webpack-dev-server	Affected: 0 , < 5.2.5 (semver) Unaffected: 5.2.5 (semver)

Credits

bjohansebas UlisesGascon ajhyndman

Show details on NVD website

JSON

To clipboard

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                "role": "CISA Coordinator",
                "timestamp": "2026-06-15T16:08:24.761216Z",
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Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

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