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CVE-2026-88011 high CVSS 8.1

Vulnerability in github.com/traefik/traefik/v2 (CVE-2026-88011)

Summary

Vulnerability in github.com/traefik/traefik/v2 (CVE-2026-88011). Confidential information can be exposed externally. Exploitable via GET /probe. Mitigation: upgrade to 2.11.56 or later.

Original description

The description as published by the source.

Summary

There is a medium severity vulnerability in Traefik's handling of request headers whose name aliases another header name. Go canonicalizes header names on dashes only, so X-Auth-User, X_Auth_User and X.Auth.User are three distinct headers to Traefik, while backends that derive variable names from header names (CGI, WSGI, PHP, NGINX, and others) collapse all of them into the same variable. A client can therefore smuggle an alias of a header that Traefik manages past the middleware managing it — for example a dot-form X.Authenticated.User alongside the canonical X-Authenticated-User written by the ForwardAuth middleware — and have such a backend read the client-supplied value instead of the identity Traefik asserted. Any header Traefik sets is exposed, not only ForwardAuth's. This is an incomplete-fix sibling of GHSA-x677-9fxg-v5c5, which blocked only the underscore form.

The mitigation is the new aliasHeadersStrategy entry point option. It defaults to keep, which preserves the previous behavior for backwards compatibility, so it must be explicitly set to delete or reject to take effect.

Traefik v1.x, the v2 releases up to v2.11.55 and the v3 releases from v3.0.0 to v3.7.11 are affected. The unmaintained lines among them will not receive a patch of their own, and the remedy for their users is to upgrade to v2.11.56 or v3.7.12 and set aliasHeadersStrategy.

Patches

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-2026-88011 has been found in github.com/traefik/traefik/v2.
Attackers can target a specific entry point like GET /probe over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 8.1/10.
What to do: upgrade github.com/traefik/traefik/v2 to 2.11.56 or later.
If unsure, ask your IT team or search "github.com/traefik/traefik/v2 CVE-2026-88011" on the vendor's site.

CVE-2026-88011 (github.com/traefik/traefik/v2) — CWE-290 / CVSS v3 8.1
Attack vector: remote (network-reachable) / no user interaction
Attack surface: GET /probe / X_Auth_User / X.Auth.User / X.Authenticated.User
Patched: 2.11.56 — 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-290) exists in github.com/traefik/traefik/v2. Attackers reach the vulnerable code path via GET /probe.

📍 Affected scope

Check the vendor advisory for the affected versions of github.com/traefik/traefik/v2. Attack surface: GET /probe / X_Auth_User / X.Auth.User / X.Authenticated.User.

🔥 Severity

Severity: High (CVSS 8.1/10). Confidential information can be exposed externally.

🔧 How to fix

Update to 2.11.56.

🛡️ 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 /probe requests with malformed payloads or SQL meta-characters. Run grep -r 'github.com/traefik/traefik/v2' . 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/v2' . | 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/v2 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 /probe' /var/log/nginx/access.log | grep -E '(unusual_payload|sqli_pattern)'

    アクセスログで GET /probe 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/v2 to 2.11.56

    ステージング環境で 2.11.56 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 /probe 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/v2
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.11.56"}]}]
go github.com/traefik/traefik/v3
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.7.12"}]}]

References

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