How severe is GHSA-mx8g-39q3-5c79?

GHSA-mx8g-39q3-5c79 has a CVSS score of 5.3/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by GHSA-mx8g-39q3-5c79?

GHSA-mx8g-39q3-5c79 affects the following packages: webpack-dev-server (npm). Ecosystems affected: npm.

How do I fix GHSA-mx8g-39q3-5c79?

Update webpack-dev-server to 5.2.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-mx8g-39q3-5c79 is resolved across your whole dependency graph.

How do I detect GHSA-mx8g-39q3-5c79 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for webpack-dev-server, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate GHSA-mx8g-39q3-5c79 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is GHSA-mx8g-39q3-5c79 actively exploited in the wild?

No public exploit code has been indexed for GHSA-mx8g-39q3-5c79 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for GHSA-mx8g-39q3-5c79?

GHSA-mx8g-39q3-5c79 has an EPSS (Exploit Prediction Scoring System) score of 0.2%, placing it in the 13th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is GHSA-mx8g-39q3-5c79?

GHSA-mx8g-39q3-5c79 is classified as CWE-346 (CWE-346), CWE-441 (CWE-441). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was GHSA-mx8g-39q3-5c79 published, and has it been updated?

GHSA-mx8g-39q3-5c79 was published on June 17, 2026 and was last updated on September 10, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦

📦 npm

Not in CISA KEV

MEDIUM severity

webpack-dev-server vulnerable to HMR WebSocket interception via permissive user proxiesGHSA-mx8g-39q3-5c79

MEDIUMFix: facebook/create-react-app#7444

GHSA-mx8g-39q3-5c79 is a medium-severity (CVSS 5.3) CWE-346 vulnerability in webpack-dev-server. A fix is available for webpack-dev-server — see the affected versions and patch details below.

Also known asCVE-2026-9595

Published

Jun 17, 2026

Updated

Sep 10, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 23, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for GHSA-mx8g-39q3-5c79.

EPSS Exploitation Probability

via FIRST.org ↗

0.2%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs13th percentile — riskier than 13% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

GHSA-mx8g-39q3-5c79 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 395,249 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

12Kother npm packages depend on this — each one inherits the vulnerability until it's patched upstream

webpack-dev-servernpm

9.5Mdownloads / week

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 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.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`webpack-dev-server`	all versions	5.2.5`npm install webpack-dev-server@5.2.5`

Affected Products

1 product · 1 configurations

Application

webpack-dev-serverwebpack.js

< 5.2.5

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for webpack-dev-server, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update webpack-dev-server to 5.2.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-mx8g-39q3-5c79 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatImportant

This vulnerability is rated as having an Important impact because improper handling of broad proxy routes allows sensitive browser data, including session tokens and origin metadata, to be exfiltrated to backend targets while circumventing server origin checks. In Red Hat environments, webpack-dev-server is primarily…

Workaround published by Red Hat

To mitigate this issue, users should avoid configuring `webpack-dev-server` with a broad proxy context (e.g., `/`) when WebSocket forwarding (`ws: true`) is enabled. Instead, define specific paths for the proxy context. Alternatively, disable WebSocket forwarding by omitting `ws: true` from the proxy entry if WebSocket functionality is not required for the proxy target. This configuration change may require restarting the `webpack-dev-server` instance to take effect.

Source: Red Hat security advisory for GHSA-mx8g-39q3-5c79 (CC BY 4.0)

Product	Fixed in	Advisory
Red Hat AMQ Broker 7.13.6	`webpack-dev-server`	RHSA-2026:66545
Red Hat AMQ Broker 7.14.1	`webpack-dev-server`	RHSA-2026:66488
Red Hat Data Grid 8.6.2	`webpack-dev-server`	RHSA-2026:41951
Red Hat Enterprise Linux 10	`rh-podman-desktop-0:1.1.2-1.el10_2`	RHSA-2026:57590
Red Hat Ansible Automation Platform 2.1	`ansible-automation-platform/automation-portal:1787047114`	RHSA-2026:56338
Red Hat Ansible Automation Platform 2.2	`ansible-automation-platform/automation-portal:1787047188`	RHSA-2026:56357
Red Hat Ansible Automation Platform 2.5	`ansible-automation-platform-25/lightspeed-rhel8:1785430174`	RHSA-2026:50357
Red Hat Ansible Automation Platform 2.6	`ansible-automation-platform-26/lightspeed-rhel9:1785775360`	RHSA-2026:50479

Frequently Asked Questions

### 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 WebSock