CVE-2023-29008

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 victims 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 doesnt 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.

Weakness

The web application does not, or can not, sufficiently verify whether a well-formed, valid, consistent request was intentionally provided by the user who submitted the request.

Affected Software

Potential Mitigations

• Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
• For example, use anti-CSRF packages such as the OWASP CSRFGuard. [REF-330]
• Another example is the ESAPI Session Management control, which includes a component for CSRF. [REF-45]
• Use the “double-submitted cookie” method as described by Felten and Zeller:
• When a user visits a site, the site should generate a pseudorandom value and set it as a cookie on the user’s machine. The site should require every form submission to include this value as a form value and also as a cookie value. When a POST request is sent to the site, the request should only be considered valid if the form value and the cookie value are the same.
• Because of the same-origin policy, an attacker cannot read or modify the value stored in the cookie. To successfully submit a form on behalf of the user, the attacker would have to correctly guess the pseudorandom value. If the pseudorandom value is cryptographically strong, this will be prohibitively difficult.
• This technique requires Javascript, so it may not work for browsers that have Javascript disabled. [REF-331]

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/111.html
• https://cwe.mitre.org/data/definitions/462.html
• https://cwe.mitre.org/data/definitions/467.html
• https://cwe.mitre.org/data/definitions/62.html

References

• https://github.com/sveltejs/kit/commit/ba436c6685e751d968a960fbda65f24cf7a82e9f
• https://github.com/sveltejs/kit/security/advisories/GHSA-gv7g-x59x-wf8f