CVE-2026-114063 in SvelteKit
Summary
by MITRE • 10/22/2026
SvelteKit (@sveltejs/kit) from 2.10.0 before 3.0.0 contains a path traversal vulnerability in the vite preview server on Windows that allows unauthenticated attackers to read files outside the prerendered output directory. Attackers who can reach the preview server through network access or a tunnel can send crafted requests to expose source code, configuration, or credentials readable by the server process.
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Analysis
by VulDB Data Team • 10/22/2026
The vulnerability identified in SvelteKit versions ranging from 2.10.0 up to but not including version 3.0.0 represents a critical security flaw within the vite preview server component when executed on Windows operating systems. This path traversal vulnerability stems from an insufficient validation of user-supplied input during file system access operations, allowing attackers to manipulate directory paths to escape the intended scope of the prerendered output directory. The core technical failure lies in how the server resolves relative paths and normalizes them against the base directory structure. On Windows systems, specific path handling quirks or inconsistencies in how forward slashes versus backslashes are processed can lead to a breakdown in boundary enforcement mechanisms. When an attacker constructs a request containing specially crafted URL parameters that include sequence characters such as dot-dot-slash sequences, the server fails to properly sanitize these inputs before attempting to locate and serve files. This oversight permits the retrieval of arbitrary files located anywhere on the file system where the server process has read permissions, effectively bypassing the isolation intended by the preview environment's design.
The operational impact of this vulnerability is severe for developers who utilize the vite preview server during local development or testing phases. Because the flaw allows unauthenticated access to sensitive resources, an attacker with network connectivity to the affected service can exfiltrate critical application assets. This includes source code repositories which may contain proprietary logic and intellectual property, configuration files that might store database connection strings, API keys, and other secrets, as well as environment variables loaded by the server process. The exposure of credentials is particularly dangerous as it can lead to further compromise of backend systems or cloud infrastructure if those credentials are reused elsewhere. Furthermore, access to source code facilitates reverse engineering efforts, enabling adversaries to identify additional vulnerabilities within the application logic that were not previously known. This risk is amplified in scenarios where developers expose their local development servers to external networks via tunneling tools for remote collaboration or testing purposes, thereby extending the attack surface beyond localhost boundaries.
From a classification perspective, this vulnerability aligns with CWE-22 Improper Limitation of a Pathname to a Restricted Directory and CWE-73 External Control of File Name or Path. These categories highlight the failure to enforce strict constraints on file system access based on user input. In terms of offensive security frameworks, this exploit technique corresponds to ATT&CK tactic TA0001 Initial Access under subtechnique T1564 Hidden Files and Directories if used for persistence, but more accurately fits within reconnaissance activities such as T1083 File and Directory Discovery or data exfiltration methods like T1005 Data from Local System. The exploitation vector is primarily network-based, requiring the attacker to send HTTP requests with manipulated path parameters to the preview server endpoint.
Mitigation strategies must focus on immediate patching and defensive configuration changes. The primary remediation step is to upgrade SvelteKit to version 3.0.0 or later where this specific path traversal issue has been addressed through improved input validation and stricter path normalization logic. For environments that cannot immediately update, it is imperative to restrict access to the vite preview server exclusively to localhost interfaces rather than binding to all network interfaces which exposes it to external networks. Additionally, developers should avoid using tunneling tools that expose local development servers to public internet unless absolutely necessary and even then only with robust authentication layers in place. Implementing a Web Application Firewall ruleset that detects common path traversal sequences such as dot-dot-slash patterns can provide an additional layer of defense during the transition period. Regular security audits of build tool configurations are also recommended to ensure that development servers do not inadvertently expose sensitive file system paths through misconfigured static asset serving mechanisms.