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CVE-2026-90711 critical CVSS 9.1

Vulnerability in proxy-addr (CVE-2026-90711)

Summary

Vulnerability in proxy-addr (CVE-2026-90711). Confidential information can be exposed externally. Exploitable via req.ip. Mitigation: upgrade to 2.0.8 or later.

Original description

The description as published by the source.

Impact

proxy-addr determines which network hops are trusted proxies so that X-Forwarded-For can be believed. When an application configures a trust subnet as an IPv4-mapped IPv6 address with a short prefix, such as ::ffff:10.0.0.0/8 (the correct spelling is ::ffff:10.0.0.0/104), the subnet compiles with all-zero leading bits and matches every IPv4 address instead of the block it names. The same happens for any IPv6 trust subnet with zero leading bits, such as ::/1.

Every unauthenticated client is then trusted as a proxy at hop 0, so proxyaddr(req, trust), and therefore req.ip and req.ips in Express, returns whatever the client sends in X-Forwarded-For. This defeats IP-based access control, rate limiting, geolocation, and audit logging. The misconfiguration compiles without any error, and the same block written correctly behaves correctly, so the difference is not visible from the configuration.

Patches

Upgrade to proxy-addr 2.0.8. An IPv4 address now matches an IPv6 trust subnet only when that subnet is a genuine IPv4-mapped subnet whose prefix covers the mapped marker.

Workarounds

Write IPv4 trust subnets in plain IPv4 notation (for example 10.0.0.0/8). If IPv4-mapped IPv6 notation is required, use the full form so the prefix covers the mapped marker (for example ::ffff:10.0.0.0/104 for the 10.0.0.0/8 block).

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-2026-90711 has been found in proxy-addr.
Attackers can target a specific entry point like req.ip over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 9.1/10.
What to do: upgrade proxy-addr to 2.0.8 or later.
If unsure, ask your IT team or search "proxy-addr CVE-2026-90711" on the vendor's site.

CVE-2026-90711 (proxy-addr) — CWE-290 / CVSS v3 9.1
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: req.ip / req.ips
Patched: 2.0.8 — apply immediately
Workaround: Write IPv4 trust subnets in plain IPv4 notation (for example 10.0.0.0/8).
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 proxy-addr. Attackers reach the vulnerable code path via req.ip without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of proxy-addr. Attack surface: req.ip / req.ips.

🔥 Severity

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

🔧 How to fix

Update to 2.0.8.

🛡️ Workaround

Workaround: Write IPv4 trust subnets in plain IPv4 notation (for example 10.0.0.0/8).

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'proxy-addr' . 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 'proxy-addr' . | 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 proxy-addr 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 temporary workaround mitigate 
    Write IPv4 trust subnets in plain IPv4 notation (for example `10.0.0.0/8`).

    パッチが適用されるまでの応急処置として、Write IPv4 trust subnets in plain IPv4 notation (for example 10.0.0.0/8). を実施。回避策の副作用 (機能低下) を確認した上で。

  3. 3
    Apply patch patch 
    Upgrade proxy-addr to 2.0.8

    ステージング環境で 2.0.8 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。

  4. 4
    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

npm proxy-addr
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.0.8"}]}]

References

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