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CVE-2026-54763 critical CVSS 10.0

Vulnerability in github.com/traefik/traefik/v2 (CVE-2026-54763)

Summary

Vulnerability in github.com/traefik/traefik/v2 (CVE-2026-54763). Confidential information can be exposed externally. Exploitable via X_Auth_User. Mitigation: upgrade to 2.11.42 or later.

Original description

The description as published by the source.

Summary

There is a high severity vulnerability in Traefik's BasicAuth, DigestAuth, and ForwardAuth
middlewares. The fix for CVE-2026-33433 stripped canonical-cased spoofed identity headers
(e.g. X-Auth-User) before writing Traefik's own value, but did not account for
underscore-variant header names (e.g. X_Auth_User), which many backends normalize
identically to the dashed form. An attacker able to reach a protected route could inject
an underscore-variant header that survives Traefik's stripping and reaches the backend
alongside — or, on the unauthenticated ForwardAuth authResponseHeaders path, instead of
— the value Traefik intended to set, spoofing identity or authorization context. This is
fixed by setting the new allowHeadersWithUnderscores: false entry point option, which
strips all headers with underscores in their names before routing.

Patches

For more information

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

Original Description

Incomplete fix for CVE-2026-33433 + CVE-2026-39858 cross-cohort: headerField underscore-variant identity spoofing in BasicAuth / DigestAuth / ForwardAuth

Summary

The fix for CVE-2026-33433 (GHSA-qr99-7898-vr7c, "BasicAuth/DigestAuth Identity Spoofing via Non-Ca…

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-2026-54763 has been found in github.com/traefik/traefik/v2.
Attackers can target a specific entry point like X_Auth_User over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 10.0/10.
What to do: upgrade github.com/traefik/traefik/v2 to 2.11.42 or later.
If unsure, ask your IT team or search "github.com/traefik/traefik/v2 CVE-2026-54763" on the vendor's site.

CVE-2026-54763 (github.com/traefik/traefik/v2) — CWE-178 / CVSS v3 10.0
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: X_Auth_User / authResponseHeaders / headerField / Header.Del
Patched: 2.11.42 — 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-178) exists in github.com/traefik/traefik/v2. Attackers reach the vulnerable code path via X_Auth_User without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of github.com/traefik/traefik/v2. Attack surface: X_Auth_User / authResponseHeaders / headerField / Header.Del.

🔥 Severity

Severity: Critical (CVSS 10.0/10). Confidential information can be exposed externally.

🔧 How to fix

Update to 2.11.42.

🛡️ 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 request patterns matching this CVE's known IOCs. 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
    Apply patch patch 
    Upgrade github.com/traefik/traefik/v2 to 2.11.42

    ステージング環境で 2.11.42 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。

  3. 3
    Post-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

go github.com/traefik/traefik/v2
[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"2.11.51"}]}]
go github.com/traefik/traefik/v3
[{"type":"SEMVER","events":[{"introduced":"3.7.0"},{"fixed":"3.7.6"}]}]
Go github.com/traefik/traefik
[{"type":"SEMVER","events":[{"introduced":"0"}]}]

References

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