CVE-2024-43796 in Express.js
Summary
by MITRE • 09/10/2024
Express.js minimalist web framework for node. In express < 4.20.0, passing untrusted user input - even after sanitizing it - to response.redirect() may execute untrusted code. This issue is patched in express 4.20.0.
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Analysis
by VulDB Data Team • 02/09/2026
The vulnerability described in CVE-2024-43796 represents a critical server-side code execution flaw within the Express.js web framework that affects versions prior to 4.20.0. This issue emerges from the improper handling of user input within the response.redirect() method, creating a path for malicious actors to inject and execute arbitrary code on the server. The vulnerability is particularly concerning because it can be exploited even when input has been sanitized, indicating a fundamental flaw in how the framework processes redirect parameters rather than a simple input validation issue.
The technical flaw manifests when developers pass user-provided data to the response.redirect() function without proper validation or encoding. Express.js versions before 4.20.0 fail to adequately sanitize the redirect URL parameter, allowing attackers to craft malicious URLs that contain executable code or exploit the framework's internal processing mechanisms. This vulnerability falls under CWE-74, which describes improper neutralization of special elements in output used by a downstream component, specifically within the context of HTTP redirects. The flaw enables attackers to bypass normal input sanitization measures and directly influence the server's execution flow through redirect operations.
The operational impact of this vulnerability is severe as it allows remote code execution on affected servers, potentially enabling full system compromise. Attackers can leverage this vulnerability to execute arbitrary commands, access sensitive data, modify server configurations, or establish persistent access points. The exploitability is high because the vulnerability can be triggered through standard web application interactions where user input is processed through redirect operations. This creates a significant risk for applications that utilize user-provided data in redirect functionality, which is common in authentication flows, URL forwarding, and various web application patterns.
Organizations should immediately upgrade to Express.js version 4.20.0 or later to remediate this vulnerability. Additionally, security teams should conduct comprehensive code reviews to identify all instances where response.redirect() is called with user-provided data, implementing proper input validation and encoding mechanisms. The mitigation strategy should include implementing strict validation of redirect URLs, utilizing absolute URLs only, and employing proper output encoding techniques. This vulnerability aligns with ATT&CK technique T1059.006 for command and script interpreter, as it allows for arbitrary code execution through the web application layer. Organizations should also consider implementing web application firewalls and runtime monitoring to detect potential exploitation attempts, while ensuring that all development practices follow secure coding guidelines to prevent similar issues in the future.