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CVE-2026-55553 high CVSS 7.5

Information Disclosure in urllib (CVE-2026-55553)

Summary

Vulnerability in urllib (CVE-2026-55553). Confidential information can be exposed externally. Exploitable via Cookie header. Mitigation: upgrade to 2.44.1 or later.

Original description

The description as published by the source.

Summary

urllib supports redirect-following through followRedirect, which is expected behavior for an HTTP client. The issue is that, when following a redirect to a different origin, urllib preserves the caller-supplied request headers verbatim, including credential-bearing headers such as Authorization, Cookie, Proxy-Authorization, and custom auth headers (x-api-key, x-auth-token, x-access-token).

If the redirect target is attacker-controlled or outside the trust boundary of the original target, credentials intended for the original origin can be delivered to the redirected origin. In a local multi-library reproduction, urllib v4.9.0 was the only tested client that stripped no headers on cross-origin redirect.

Affected behavior

Confirmed against urllib v4.9.0. The relevant code is in #requestInternal (src/HttpClient.ts:639-656):

     // https://developer.mozilla.org/en-US/docs/Web/HTTP/Redirections
      if (RedirectStatusCodes.includes(res.statusCode) && maxRedirects > 0 && requestContext.redirects < maxRedirects) {
        if (res.headers.location) {
          requestContext.redirects++;
          const nextUrl = new URL(res.headers.location, requestUrl.href);
          // Ensure the response is consumed
          await response.body.arrayBuffer();
          debug(
            'Request#%d got response, status: %s, headers: %j, timing: %j, redirect to %s',…

Source: GitHub Security Advisories (Global) 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-2026-55553 has been found in urllib.
Attackers can target a specific entry point like Cookie header over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 7.5/10.
What to do: upgrade urllib to 2.44.1 or later.
If unsure, ask your IT team or search "urllib CVE-2026-55553" on the vendor's site.

CVE-2026-55553 (urllib) — CWE-200 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: Cookie header / followRedirect / Authorization / Cookie
Patched: 2.44.1 — 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

Information disclosure (CWE-200) exists in urllib. Attackers reach the vulnerable code path via Cookie header without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of urllib. Attack surface: Cookie header / followRedirect / Authorization / Cookie.

🔥 Severity

Severity: High (CVSS 7.5/10). Confidential information can be exposed externally.

🔧 How to fix

Update to 2.44.1.

🛡️ 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 'urllib' . 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 'urllib' . | 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 urllib 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 urllib to 2.44.1

    ステージング環境で 2.44.1 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

npm urllib
[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"2.44.1"}]}]

References

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