Vulnerability in undici (CVE-2026-9675)
Summary
Vulnerability in undici (CVE-2026-9675). Risk of unauthorized operations or information disclosure. Exploitable via maxPayloadSize. Mitigation: upgrade to 8.5.0 or later.
Original description
The description as published by the source.
Impact
The undici WebSocket client enforces maxPayloadSize per-frame but does not enforce the cumulative size of fragmented uncompressed messages. A malicious WebSocket server can stream many small fragments that each pass per-frame validation but collectively exceed the configured limit, causing unbounded memory growth in the client process. The result is memory exhaustion and a denial of service.
Affected applications are those using the undici WebSocket client (new WebSocket(...)) that can be induced to connect to an attacker-controlled or compromised WebSocket endpoint.
This is a regression specific to undici 8.1.0. The 6.25.0 line shipped the equivalent cumulative check from the start and is unaffected. The 7.x line never had the maxPayloadSize feature and is also unaffected.
Patches
Upgrade to undici >= 8.5.0.
Workarounds
No workaround is available. The fix must be applied through an upgrade.
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-2026-9675 has been found in undici.
Attackers can target a specific entry point like maxPayloadSize over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 7.5/10.
What to do: upgrade undici to 8.5.0 or later.
If unsure, ask your IT team or search "undici CVE-2026-9675" on the vendor's site.
CVE-2026-9675 (undici) — CWE-400 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: maxPayloadSize
Patched: 8.5.0 — apply immediately
Workaround: No workaround is available.
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-400) exists in undici. Attackers reach the vulnerable code path via maxPayloadSize without authentication.
Check the vendor advisory for the affected versions of undici. Attack surface: maxPayloadSize.
Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.
Update to 8.5.0.
Workaround: No workaround is available.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'undici' . 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 'undici' . | 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
undici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
No workaround is available.パッチが適用されるまでの応急処置として、No workaround is available. 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 undici to 8.5.0ステージング環境で 8.5.0 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-2026-9675 node-undici
References
- advisory nvd.nist.gov
- package github.com
- web cna.openjsf.org
- web github.com
- web github.com