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webpack-dev-server vulnerable to cross-origin source code exposure on non-HTTPS origins

Moderate severity GitHub Reviewed Published May 11, 2026 in webpack/webpack-dev-server • Updated May 18, 2026

Package

npm webpack-dev-server (npm)

Affected versions

<= 5.2.3

Patched versions

5.2.4

Description

Impact

When webpack-dev-server is running on a non-HTTPS origin (the default), cross-origin requests from malicious websites can load the dev server's JavaScript bundles via <script> tags. The fix introduced in v5.2.1 (CVE-2025-30359) relied on Sec-Fetch-Mode and Sec-Fetch-Site request headers to block these requests, but browsers only send these headers for potentially trustworthy origins. Over plain HTTP, the headers are absent and the check is bypassed.

An attacker who knows the dev server's host, port, and output path can exfiltrate all module source code by intercepting the webpack runtime's module registration.

This does not affect Chrome 142+ (and other Chromium-based browsers) due to local network access restrictions.

Patches

Patched in webpack-dev-server >= 5.2.4 by setting Cross-Origin-Resource-Policy: same-origin on responses.

Workarounds

Run the dev server with HTTPS enabled (--https or server.type: 'https' in config).

Resources

References

@alexander-akait alexander-akait published to webpack/webpack-dev-server May 11, 2026
Published by the National Vulnerability Database May 12, 2026
Published to the GitHub Advisory Database May 18, 2026
Reviewed May 18, 2026
Last updated May 18, 2026

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:N/A:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(27th percentile)

Weaknesses

Exposed Dangerous Method or Function

The product provides an Applications Programming Interface (API) or similar interface for interaction with external actors, but the interface includes a dangerous method or function that is not properly restricted. Learn more on MITRE.

CVE ID

CVE-2026-6402

GHSA ID

GHSA-79cf-xcqc-c78w

Source code

Credits

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