CVE-2026-93903 in LiteSpeed Web Server
Summary
by MITRE • 09/30/2026
LiteSpeed Web Server (LSWS) before 6.3.7 build 1 mishandles internal redirect URL validation in a certain "corner case."
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Analysis
by VulDB Data Team • 09/30/2026
The vulnerability identified in LiteSpeed Web Server versions prior to 6.3.7, specifically affecting builds earlier than the fixed version, centers on an improper handling of internal redirect URL validation within specific edge cases. This flaw resides in the core request processing logic where the server manages URI redirections internally before serving content or forwarding requests to backend applications. The issue arises when the web server processes a sequence of redirects that involve complex path manipulations or non-standard URI structures, leading to a state where the internal redirect mechanism fails to adequately sanitize or validate the target URL against expected security boundaries. This misconfiguration allows an attacker to exploit the gap in validation logic by crafting specific HTTP requests that trigger unintended redirection behaviors, potentially bypassing access controls or exposing sensitive server internals.
From a technical perspective, this vulnerability is classified under CWE-20 Improper Input Validation and often relates to path traversal concepts found in CWE-22 if it leads to unauthorized file system access, although the primary impact here is likely related to request routing integrity. The ATT&CK framework categorizes such behaviors under techniques involving resource hijacking or potential privilege escalation depending on how the redirect is leveraged within the application architecture. When an internal redirect occurs, the server typically strips certain headers and resets parts of the request context. If the URL validation logic is flawed in these corner cases, it may allow for header injection, open redirection to malicious external sites, or more critically, bypassing authentication mechanisms that rely on specific URI patterns being strictly enforced before reaching backend handlers like PHP-FPM or application servers.
The operational impact of this vulnerability can vary significantly based on the deployment configuration and the sensitivity of the hosted applications. In a typical web hosting environment, an attacker could potentially use crafted redirect chains to evade Web Application Firewalls that inspect only initial request URIs but not subsequent internal redirects. This evasion technique allows malicious payloads to reach backend services without triggering standard security rules. Furthermore, if the server is configured with sensitive administrative interfaces or API endpoints protected by IP whitelisting or specific URI patterns, an attacker might manipulate the redirect logic to access these resources from unauthorized networks. In severe scenarios involving misconfigured document roots, this could lead to information disclosure where internal files not intended for public access are served due to incorrect path resolution during the redirect process.
Mitigation strategies primarily involve upgrading the LiteSpeed Web Server software to version 6.3.7 build or later, which contains the necessary patches to correct the URL validation logic in these edge cases. Administrators should verify their current build number through the server status page and ensure that automatic updates are enabled if available within their licensing tier. In environments where immediate patching is not feasible due to compatibility concerns with existing applications, temporary mitigations include implementing strict input filtering at a reverse proxy layer such as Nginx or Apache in front of LiteSpeed to sanitize redirect headers before they reach the vulnerable server component. Additionally, reviewing and hardening access control lists for sensitive directories can reduce the risk profile associated with potential bypass attempts until the software is fully updated. Regular security audits focusing on how redirects are handled within custom configurations will also help identify any residual risks or misconfigurations that could exacerbate this vulnerability class.