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CVE-2026-88008 critical CVSS 9.1

Vulnerability in github.com/traefik/traefik/v3 (CVE-2026-88008)

Summary

Vulnerability in github.com/traefik/traefik/v3 (CVE-2026-88008). Confidential information can be exposed externally. Exploitable via GET /public. Mitigation: upgrade to 3.7.13 or later.

Original description

The description as published by the source.

Summary

There is a high-severity request-smuggling vulnerability in Traefik's handling of the HTTP/1.1 Upgrade mechanism. Since Traefik moved to unencrypted HTTP/2 with prior knowledge (Go 1.24), a client-initiated Upgrade: h2c request header and its connection-specific HTTP2-Settings header were forwarded to the backend. A backend that honours the h2c upgrade and answers 101 Switching Protocols puts Traefik into a raw byte tunnel that bypasses the router and the entire middleware chain (authentication, IPAllowList, rate limiting) on a shared backend. The fix stops forwarding the Upgrade: h2c token and the HTTP2-Settings header; Upgrade: websocket is unaffected. Exploitation requires a backend that upgrades h2c without validating the Connection listing; common off-the-shelf servers were not exploitable in testing.

Traefik v3.4.2 through v3.6 are end-of-life and are also affected; users on those versions must upgrade to v3.7.13.

Patches

For more information

If you have any questions or comments about this advisory, please open an issue.

Original Description

Summary

Traefik's default HTTP reverse proxy forwards arbitrary Connection: Upgrade / Upgrade: requests to the backend. Upgrade tokens are not restricted to protocols explicitly supported by Traefik.

This is exploitable whe…

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-2026-88008 has been found in github.com/traefik/traefik/v3.
Attackers can target a specific entry point like GET /public over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 9.1/10.
What to do: upgrade github.com/traefik/traefik/v3 to 3.7.13 or later.
If unsure, ask your IT team or search "github.com/traefik/traefik/v3 CVE-2026-88008" on the vendor's site.

CVE-2026-88008 (github.com/traefik/traefik/v3) — CWE-444 / CVSS v3 9.1
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: GET /public / GET /admin / Upgrade / Connection
Patched: 3.7.13 — apply immediately
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.

❓ What is the problem

A vulnerability (CWE-444) exists in github.com/traefik/traefik/v3. Attackers reach the vulnerable code path via GET /public without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of github.com/traefik/traefik/v3. Attack surface: GET /public / GET /admin / Upgrade / Connection.

🔥 Severity

Severity: Critical (CVSS 9.1/10). Confidential information can be exposed externally.

🔧 How to fix

Update to 3.7.13.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual GET /public requests with malformed payloads or SQL meta-characters. Run grep -r 'github.com/traefik/traefik/v3' . 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

  1. 1
    Identify exposure identify 
    grep -r 'github.com/traefik/traefik/v3' . | 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 github.com/traefik/traefik/v3 を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Hunt for indicators of compromise detect 
    grep 'GET /public' /var/log/nginx/access.log | grep -E '(unusual_payload|sqli_pattern)'

    アクセスログで GET /public への異常なリクエスト (不正な認証ヘッダ・SQLメタ文字)を過去 30〜90日分捜索。WAF/SIEM があれば該当パスのアラート発火履歴を確認。

  3. 3
    Apply patch patch 
    Upgrade github.com/traefik/traefik/v3 to 3.7.13

    ステージング環境で 3.7.13 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と、Step 2 で見つけた異常検知の続報チェックを含めること。

  4. 4
    Post-deployment verification verify 
    Replay attack against GET /public on staging to confirm patch closes the vector

    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 Step 2 と同じログクエリでアラート再発が無いか継続監視。

Affected packages

go github.com/traefik/traefik/v3
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.7.13"}]}]
go github.com/traefik/traefik/v2
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.11.57"}]}]

References

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