Vulnerability in webpack-dev-server (CVE-2026-9595)
Summary
Vulnerability in webpack-dev-server (CVE-2026-9595). Risk of unauthorized operations or information disclosure. Exploitable via Origin. Mitigation: upgrade to 5.2.5 or later.
Original description
The description as published by the source.
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.
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-9595 has been found in webpack-dev-server.
Attackers can target a specific entry point like Origin over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 5.3/10.
What to do: upgrade webpack-dev-server to 5.2.5 or later.
If unsure, ask your IT team or search "webpack-dev-server CVE-2026-9595" on the vendor's site.
CVE-2026-9595 (webpack-dev-server) — CWE-346 / CVSS v3 5.3
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: Origin / context
Patched: 5.2.5 — apply immediately
Workaround: Scope user-defined proxy context to specific paths instead of /, or omit ws: true from the proxy entry when WebSocket forwarding is not required.
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-346) exists in webpack-dev-server. Attackers reach the vulnerable code path via Origin without authentication.
Check the vendor advisory for the affected versions of webpack-dev-server. Attack surface: Origin / context.
Severity: Medium (CVSS 5.3/10). Risk of unauthorized operations or information disclosure.
Update to 5.2.5.
Workaround: Scope user-defined proxy context to specific paths instead of /, or omit ws: true from the proxy entry when WebSocket forwarding is not required.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'webpack-dev-server' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
-
1Identify exposure identify
grep -r 'webpack-dev-server' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
webpack-dev-serverを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply temporary workaround mitigate
Scope user-defined proxy `context` to specific paths instead of `/`, or omit `ws: true` from the proxy entry when WebSocket forwarding is not required.パッチが適用されるまでの応急処置として、Scope user-defined proxy
contextto specific paths instead of/, or omitws: truefrom the proxy entry when WebSocket forwarding is not required. を実施。回避策の副作用 (機能低下) を確認した上で。 -
3Apply patch patch
Upgrade webpack-dev-server to 5.2.5ステージング環境で 5.2.5 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
4Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Ubuntu UBUNTU-CVE-2026-9595 node-webpack
References
- advisory cna.openjsf.org
- advisory github.com
- advisory nvd.nist.gov
- advisory github.com
- package github.com
- patch github.com
- patch github.com
- patch github.com
- web github.com