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CVE-2026-88004 high CVSS 7.4

Vulnerability in github.com/traefik/traefik/v3 (CVE-2026-88004)

Summary

Vulnerability in github.com/traefik/traefik/v3 (CVE-2026-88004). Confidential information can be exposed externally. Exploitable via aliasHeadersStrategy. Mitigation: upgrade to 3.7.13 or later.

Original description

The description as published by the source.

Summary

Traefik's entrypoint defenses against spoofed trusted header names — aliasHeadersStrategy / underscoreHeadersStrategy in delete or reject mode, and the default forwardedHeaders stripping of client-supplied X-Forwarded-* — scan req.Header only and never req.Trailer. An unauthenticated client can therefore smuggle a sanitized name (an aliasing spelling such as X_Auth_User, or a trusted name such as X-Forwarded-Prefix) as an HTTP/1.1 chunked trailer or an HTTP/2 trailer: reject does not return its documented 400, delete does not remove the name, and Traefik's reverse proxy forwarded the trailer to the backend — with an attacker-chosen value whenever a body-buffering middleware (the retry middleware with status codes, or the buffering middleware) reads the body before the proxy clone. Backends that merge trailers into their header namespace then act on the smuggled name. The fix stops forwarding request trailer values to the backend; the declared trailer names are still forwarded as permitted by RFC 9110 section 6.6.2.

Traefik v2 is not affected: the defect is in the custom reverse proxy introduced in v3 (pkg/proxy/httputil), and v2 uses the Go standard library's httputil.ReverseProxy, which does not forward request trailer values to the backend. Affected v3 lines from v3.2.0 through v3.7.12 include the end-of-life v3.2 through v3.6 lines, which will not receive a fix on their own line; the remedy for those users is to upgrade to v3.…

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-2026-88004 has been found in github.com/traefik/traefik/v3.
Attackers can target a specific entry point like aliasHeadersStrategy over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 7.4/10.
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-2026-88004" on the vendor's site.

CVE-2026-88004 (github.com/traefik/traefik/v3) — CWE-436 / CVSS v3 7.4
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: aliasHeadersStrategy / underscoreHeadersStrategy / delete / reject
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-436) exists in github.com/traefik/traefik/v3. Attackers reach the vulnerable code path via aliasHeadersStrategy without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of github.com/traefik/traefik/v3. Attack surface: aliasHeadersStrategy / underscoreHeadersStrategy / delete / reject.

🔥 Severity

Severity: High (CVSS 7.4/10). 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 request patterns matching this CVE's known IOCs. 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
    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/v3
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.7.13"}]}]

References

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