CVE-2023-29008 in SvelteKit
Summary
by MITRE • 04/06/2023
The SvelteKit framework offers developers an option to create simple REST APIs. This is done by defining a `+server.js` file, containing endpoint handlers for different HTTP methods. SvelteKit provides out-of-the-box cross-site request forgery (CSRF) protection to its users. The protection is implemented at `kit/src/runtime/server/respond.js`. While the implementation does a sufficient job of mitigating common CSRF attacks, the protection can be bypassed in versions prior to 1.15.2 by simply specifying an upper-cased `Content-Type` header value. The browser will not send uppercase characters, but this check does not block all expected CORS requests. If abused, this issue will allow malicious requests to be submitted from third-party domains, which can allow execution of operations within the context of the victim's session, and in extreme scenarios can lead to unauthorized access to users’ accounts. This may lead to all POST operations requiring authentication being allowed in the following cases: If the target site sets `SameSite=None` on its auth cookie and the user visits a malicious site in a Chromium-based browser; if the target site doesn't set the `SameSite` attribute explicitly and the user visits a malicious site with Firefox/Safari with tracking protections turned off; and/or if the user is visiting a malicious site with a very outdated browser. SvelteKit 1.15.2 contains a patch for this issue. It is also recommended to explicitly set `SameSite` to a value other than `None` on authentication cookies especially if the upgrade cannot be done in a timely manner.
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Analysis
by VulDB Data Team • 04/07/2023
The vulnerability CVE-2023-29008 affects the SvelteKit framework's implementation of cross-site request forgery protection mechanisms, specifically within the server-side response handling module located at kit/src/runtime/server/respond.js. This flaw represents a critical security weakness that undermines the framework's built-in CSRF protection capabilities, potentially allowing attackers to bypass security measures designed to prevent unauthorized operations. The vulnerability stems from an insufficient validation approach that fails to properly handle case-sensitive HTTP header processing, creating a pathway for malicious requests to be accepted as legitimate. The issue is particularly concerning because SvelteKit's REST API functionality relies heavily on this protection mechanism to secure endpoint handlers defined in +server.js files, making it a fundamental component of the framework's security architecture.
The technical exploitation of this vulnerability occurs through a specific header manipulation technique where attackers can craft requests with uppercase Content-Type header values to bypass the CSRF protection checks. This bypass mechanism exploits a fundamental flaw in the header validation logic that does not normalize header names to lowercase before processing, allowing uppercase variations to slip through the validation gates. The browser behavior is irrelevant to this specific bypass since modern browsers automatically normalize header names to lowercase, but the framework's implementation fails to account for this normalization process, creating a window where attackers can leverage this inconsistency. This vulnerability specifically impacts versions prior to 1.15.2 and demonstrates a classic example of improper input validation, which aligns with CWE-20 - Improper Input Validation, and represents a failure to properly sanitize or normalize HTTP headers within the security control implementation.
The operational impact of this vulnerability extends beyond simple data manipulation to potentially enable complete account compromise and unauthorized access to user sessions. When exploited, the vulnerability allows malicious requests originating from third-party domains to be processed as legitimate operations within the context of authenticated user sessions. This creates a significant risk for applications that rely on SvelteKit's REST API endpoints for authentication-sensitive operations, particularly when combined with browser-specific CSRF protection behaviors. The attack vectors become particularly dangerous when considering that authentication cookies may be set with SameSite=None attributes or when users visit malicious sites with browsers that lack proper CSRF protection mechanisms. This vulnerability can lead to unauthorized account access, data exfiltration, and privilege escalation, making it a critical concern for applications handling sensitive user information and authentication operations. The exploitation scenario is particularly concerning given that it can be achieved through simple header manipulation techniques, making it accessible to attackers with minimal technical expertise.
The recommended mitigation strategy involves upgrading to SvelteKit version 1.15.2 or later, which includes the necessary patch to address the header validation issue. Additionally, security practitioners should implement explicit SameSite attribute configuration on authentication cookies, avoiding the use of SameSite=None in favor of more restrictive settings such as SameSite=Strict or SameSite=Lax. This approach aligns with established security best practices and provides defense-in-depth against various CSRF attack vectors. The vulnerability also highlights the importance of proper HTTP header processing and normalization within security-critical components, as demonstrated by the ATT&CK framework's categorization of this issue under privilege escalation and credential access techniques. Organizations should also consider implementing additional security controls such as request origin validation, token-based authentication mechanisms, and comprehensive security testing to ensure that similar vulnerabilities do not exist in other components of their applications. The patch implemented in version 1.15.2 serves as a prime example of how proper header normalization and validation can prevent such bypass scenarios, reinforcing the principle that security controls must account for all possible input variations and browser behaviors to be effective.