Summary
follow-redirects: Cross-realm sensitiveHeaders arrays are discarded and custom credentials can follow redirects
follow-redirects 1.16.0 and 1.16.1 validate the documented sensitiveHeaders option with instanceof Array. An array created in another JavaScript realm is silently replaced with an empty list, so a caller-declared custom credential header can be forwarded to an attacker-controlled cross-origin redirect destination.
Details
Affected versions
The sensitiveHeaders option was introduced in 1.16.0. Published 1.16.0 and 1.16.1 both reproduced, giving a tested affected range of 1.16.0 through 1.16.1. The source checkout was pinned at revision 46301256333c90b7faac7aa126effe72ec16d16e; the exact npm 1.16.1 artifact reproduced independently.
Root cause
index.js resets options.sensitiveHeaders when its local isArray() helper returns false. That helper uses value instanceof Array, which depends on realm identity. The same file already uses Array.isArray(options.headers), which correctly recognizes arrays across realms.
Suggested remediation
Use Array.isArray(value) for sensitiveHeaders, then validate and normalize each member as a header-name string. Add same-realm and node:vm cross-realm tests for cross-origin redirects, including the array-form headers representation. Verify that custom sensitive names are removed while unrelated headers remain unchanged.
Duplicate review
The public advisory history contains other sensitive-header findings, including array-form headers and regular-expression handling, but focused repository searches found no report describing cross-realm validation as of 2026-10-25. A private or differently worded report may already exist.
Proof of concept
Start two loopback HTTP servers. The first returns a 302 redirect to the second. Send X-API-Key and list that name in sensitiveHeaders, then compare a normal array with a genuine cross-realm array created by:
const vm = require('node:vm');
const sensitiveHeaders = vm.runInNewContext(`['X-API-Key']`);
Observed against both source and the exact npm 1.16.1 package:
- Same-realm ['X-API-Key']: the redirect target did not receive the key.
- Cross-realm ['X-API-Key']: Array.isArray(value) was true, value instanceof Array was false, and the redirect target received X-API-Key.
- An unrelated X-Harmless header remained present in both cases.
The complete 3.5 KB loopback-only harness and raw JSON output are available privately.
Impact
custom credential disclosure. Exploitation requires a direct caller or wrapper that preserves a cross-realm sensitiveHeaders array, a custom credential listed in that option, and an attacker-controlled or compromised endpoint that returns a cross-origin redirect. The directly demonstrated result is disclosure of the custom header value, potentially exposing an API key or service token until revocation.
Built-in Authorization, Proxy-Authorization, and Cookie protections remained effective. Exact Axios 1.20.0 with follow-redirects 1.16.1 did not reproduce because Axios normalized the array; this report does not claim that Axios is affected. No third-party service was tested.
CVE-2026-116689 has a CVSS score of 5.9 (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 (1.16.2); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
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Frequently Asked Questions
- What is CVE-2026-116689? CVE-2026-116689 is a high-severity security vulnerability in follow-redirects (npm), affecting versions >= 1.16.0, <= 1.16.1. It is fixed in 1.16.2.
- How severe is CVE-2026-116689? CVE-2026-116689 has a CVSS score of 5.9 (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.
- Which versions of follow-redirects are affected by CVE-2026-116689? follow-redirects (npm) versions >= 1.16.0, <= 1.16.1 is affected.
- Is there a fix for CVE-2026-116689? Yes. CVE-2026-116689 is fixed in 1.16.2. Upgrade to this version or later.
- Is CVE-2026-116689 exploitable, and should I be worried? Whether CVE-2026-116689 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
- What actually determines whether CVE-2026-116689 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.
- How do I fix CVE-2026-116689? Upgrade
follow-redirectsto 1.16.2 or later.