Summary
Feathers has an open redirect in OAuth callback enables account takeover
Description
The redirect query parameter is appended to the base origin without validation, allowing attackers to steal access tokens via URL authority injection. This leads to full account takeover, as the attacker obtains the victim's access token and can impersonate them.
The application constructs the final redirect URL by concatenating the base origin with the user-supplied redirect parameter:
// https://github.com/feathersjs/feathers/blob/dove/packages/authentication-oauth/src/service.ts#L158C3-L176C4
const { redirect } = query;
...
session.redirect = redirect;
// https://github.com/feathersjs/feathers/blob/dove/packages/authentication-oauth/src/strategy.ts#L98
const redirectUrl = `${redirect}${queryRedirect}`;
Where:
redirect= base origin from config (e.g.,https://target.com)queryRedirect= user input from?redirect=parameter
This is exploitable when the origins array is configured and origin values do not end with /. An attacker can supply @attacker.com as the redirect value results in https://[email protected]#access_token=..., where the browser interprets attacker.com as the host, leading to full account takeover.
Credits: Abdelwahed Madani Yousfi (@vvxhid) / Edoardo Geraci (@b0-n0-b0) / Thomas Rinsma (@ThomasRinsma) From Codean Labs.
Impact
Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites. Typical impact: phishing and credential harvesting via a trusted domain.
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-2026-27191? CVE-2026-27191 is a high-severity open redirect vulnerability in @feathersjs/authentication-oauth (npm), affecting versions <= 5.0.39. It is fixed in 5.0.40. Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites.
- Which versions of @feathersjs/authentication-oauth are affected by CVE-2026-27191? @feathersjs/authentication-oauth (npm) versions <= 5.0.39 is affected.
- Is there a fix for CVE-2026-27191? Yes. CVE-2026-27191 is fixed in 5.0.40. Upgrade to this version or later.
- Is CVE-2026-27191 exploitable, and should I be worried? Whether CVE-2026-27191 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-2026-27191 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-2026-27191? Upgrade
@feathersjs/authentication-oauthto 5.0.40 or later.