CVE-2024-9266: Express Response Open Redirect Vulnerability

CVE-2024-9266 Overview

CVE-2024-9266 is an open redirect vulnerability [CWE-601] affecting the Express web framework for Node.js. The flaw resides in the Express Response object and impacts versions from 3.4.5 before 4.0.0. Attackers can craft URLs that use a trusted Express-based application to redirect victims to attacker-controlled destinations. This behavior enables phishing, credential theft, and downstream social engineering attacks that abuse the trust users place in the legitimate host domain.

Critical Impact
Attackers can leverage a trusted Express application as a redirection proxy to send users to malicious sites, undermining URL-based trust decisions and enabling phishing campaigns.

Affected Products

Express versions from 3.4.5 up to (not including) 4.0.0
Node.js applications using the vulnerable Express Response redirect functionality
Downstream frameworks and services embedding affected Express releases

Discovery Timeline

2024-10-03 - CVE-2024-9266 published to the National Vulnerability Database (NVD)
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2024-9266

Vulnerability Analysis

The vulnerability is an open redirect classified under [CWE-601]. Express exposes a res.redirect() method on the Response object. Affected versions accept user-supplied input as the redirect target without sufficient validation of the destination host. An attacker who can influence the redirect argument, typically via a query parameter or path segment, can steer users to an arbitrary external URL.

Exploitation requires user interaction, such as clicking a crafted link. The resulting redirect originates from a trusted domain, so security controls that rely on host reputation or URL allowlists can be bypassed. The attack does not compromise the Express server itself but weaponizes it as a redirection primitive against its users.

Open redirects are frequently chained with phishing kits, OAuth flow abuse, and token exfiltration. The scope change reflected in the vulnerability metrics indicates that impact extends beyond the vulnerable application to affect the browsing session and any authenticated context the user reaches.

Root Cause

The root cause is insufficient validation of the destination URL passed to Express's redirect handling in the Response object. When application code forwards untrusted input directly into res.redirect() or similar patterns without allowlisting the target host, the framework returns an HTTP 302 response containing the attacker-supplied Location header.

Attack Vector

The attack vector is network-based and requires user interaction. A typical exploitation flow works as follows:

The attacker identifies an Express endpoint that echoes a redirect, next, url, or return parameter into res.redirect().
The attacker crafts a URL such as https://trusted-app.example.com/login?next=https://attacker.example/phish.
The victim clicks the link, trusting the visible host.
The Express application issues a 302 Found response with a Location header pointing at the attacker-controlled site.
The browser follows the redirect and delivers the victim to the phishing or malware page.

Refer to the HeroDevs advisory for CVE-2024-9266 for additional technical detail.

Detection Methods for CVE-2024-9266

Indicators of Compromise

HTTP 302 responses from Express endpoints where the Location header points to an external domain not on an approved allowlist.
Access log entries containing redirect query parameters, such as ?next=, ?url=, ?redirect=, or ?returnTo=, with values that decode to external URLs.
Referer headers on external phishing infrastructure that trace back to trusted Express-hosted domains.

Detection Strategies

Inventory Node.js applications and identify any dependency tree entries resolving to Express 3.4.5 through versions prior to 4.0.0.
Perform static analysis for direct use of req.query, req.params, or req.body values passed into res.redirect() without validation.
Deploy web application firewall (WAF) signatures that flag redirect parameters containing absolute URLs pointing to external hosts.

Monitoring Recommendations

Log all outbound Location header values from Express endpoints and alert on off-domain redirects.
Correlate reports of phishing emails referencing corporate domains with server-side redirect telemetry.
Monitor URL reputation feeds for corporate hostnames appearing as intermediaries in phishing chains.

How to Mitigate CVE-2024-9266

Immediate Actions Required

Upgrade Express to version 4.0.0 or later on all affected Node.js applications.
Audit application code for calls to res.redirect() that consume unvalidated user input and refactor to use a server-side allowlist.
Communicate the phishing risk to users of any application that cannot be patched immediately.

Patch Information

Upgrade the express dependency to a version at or above 4.0.0. Consult the HeroDevs advisory for CVE-2024-9266 for guidance on supported upgrade paths and long-term support options for legacy Express 3.x deployments.

Workarounds

Replace direct pass-through redirects with a lookup table that maps opaque tokens to approved internal destinations.
Validate any user-supplied redirect target against a strict allowlist of hostnames before invoking res.redirect().
Reject redirect targets that begin with //, http://, or https:// when only relative paths are expected.

bash

# Configuration example: upgrade Express to a fixed release
npm install express@^4.0.0
npm audit --production