CVE-2026-9595: Impact: When a user-configured proxy on webpack-dev-server has a broad context (e.g

Q: How do I fix CVE-2026-9595?

webpack-dev-server: upgrade to 5.2.5. Exact commands for each OS are on this page.

Q: Is CVE-2026-9595 being exploited?

CVE-2026-9595 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-9595 affect?

CVE-2026-9595 affects webpack-dev-server. Severity is medium (CVSS 5.3). 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 hea

Q: How urgent is CVE-2026-9595?

Priority 25/100. Remotely exploitable, no login, no user action

Routine

MEDIUM 5.3REMOTEUPGRADE

CVE-2026-9595 is a medium-severity flaw (CVSS 5.3) affecting webpack-dev-server. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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. Workar

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.2% (top 95%)
CISA exploited list	No
Weakness	CWE-346, CWE-441
Published	2026-06-15
Last modified	2026-06-17

Publisher (CNA): openjs · Vendor: webpack.js

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-06-15 16:16 UTCPublished CVE record published
2026-06-17 11:05 UTCUpdated Record last modified

webpack.js webpack-dev-server UPGRADE

Affected: < 5.2.5

Fixed in: 5.2.5

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy webpack-dev-server || rpm -q webpack-dev-server || webpack-dev-server --version

2. UPGRADE to 5.2.5 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade webpack-dev-server

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade webpack-dev-server

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-9595?

webpack-dev-server: upgrade to 5.2.5. Exact commands for each OS are on this page.

Is CVE-2026-9595 being exploited?

CVE-2026-9595 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-9595 affect?

CVE-2026-9595 affects webpack-dev-server. Severity is medium (CVSS 5.3). 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 hea

How urgent is CVE-2026-9595?

Priority 25/100. Remotely exploitable, no login, no user action

Software pages

Webpack vulnerabilities

Related CVEs

CVE-2026-14620 MEDIUM 4.7 UPGRADE webpack-dev-server versions 5.2.5 and earlier expose two internal developer endpoints, /webpack-dev-server/ope
CVE-2026-14631 MEDIUM 5.3 UPGRADE webpack-dev-server versions 5.2.5 and earlier terminate the whole Node.js process when an unauthenticated peer

References

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