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webpack-dev-server vulnerable to denial of service via a malformed Host or Origin header

Moderate severity GitHub Reviewed Published Jul 3, 2026 in webpack/webpack-dev-server • Updated Jul 20, 2026

Package

npm webpack-dev-server (npm)

Affected versions

<= 5.2.5

Patched versions

5.2.6

Description

Impact

An unauthenticated peer that can reach the webpack-dev-server process can terminate it by sending either a normal HTTP request with a malformed Host header, or a WebSocket upgrade to the default /ws endpoint with a malformed Origin header. The malformed header triggers an uncaught exception in the host-validation path and crashes the dev server process.

Patches

Fixed in webpack-dev-server 5.2.6 by treating malformed Host and Origin header values as invalid rather than throwing (see PR #5699).

Workarounds

Keep the dev server bound to localhost (the default) and do not expose it to untrusted networks.

References

@UlisesGascon UlisesGascon published to webpack/webpack-dev-server Jul 3, 2026
Published by the National Vulnerability Database Jul 3, 2026
Published to the GitHub Advisory Database Jul 20, 2026
Reviewed Jul 20, 2026
Last updated Jul 20, 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
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low

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:L/PR:N/UI:N/S:U/C:N/I:N/A:L

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.
(42nd percentile)

Weaknesses

Improper Input Validation

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. Learn more on MITRE.

Uncaught Exception

An exception is thrown from a function, but it is not caught. Learn more on MITRE.

CVE ID

CVE-2026-14631

GHSA ID

GHSA-m28w-2pqf-7qgj

Source code

Credits

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