CVE-2023-29003 is a high-severity (CVSS 8.8) CWE-184 vulnerability in @sveltejs/kit. 1 public exploit reference exists, so weaponization risk is real. A fix is available for @sveltejs/kit — see the affected versions and patch details below.
SvelteKit has Insufficient Cross-Site Request Forgery Protection
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA’s SSVC triage for CVE-2023-29003.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2023-29003 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,567 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
@sveltejs/kitnpmDescription
Summary
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 it’s users. The protection is implemented at kit/src/runtime/server/respond.js#L52. While the implementation does a sufficient job in mitigating common CSRF attacks, the protection can be bypassed by simply specifying a different Content-Type header value.
Details
The CSRF protection is implemented using the code shown below.
const forbidden =
// (1)
request.method === 'POST' &&
// (2)
request.headers.get('origin') !== url.origin &&
// (3)
is_form_content_type(request);
if (forbidden) {
// (4)
const csrf_error = error(403, `Cross-site ${request.method} form submissions are forbidden`);
if (request.headers.get('accept') === 'application/json') {
return json(csrf_error.body, { status: csrf_error.status });
}
return text(csrf_error.body.message, { status: csrf_error.status });
}
If the incoming request specifies a POST method (1), the protection will compare the server’s origin with the value of the HTTP Origin header (2). A mismatch between these values signals that a potential attack has been detected. The final check is performed on the request’s Content-Type header (3) whether the value is either application/x-www-form-urlencoded or multipart/form-data (kit/src/utils/http.js#L71). If all the previous checks pass, the request will be rejected with an 403 error response (4).
The is_form_content_type validation is not sufficient to mitigate all possible variations of this type of attack. If a CSRF attack is performed with the Content-Type header set to text/plain, the protection will be circumvented and the request will be processed by the endpoint handler.
Impact
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.
Remediation
SvelteKit 1.15.1 updates the is_form_content_type function call in the CSRF protection logic to include text/plain.
As additional hardening of the CSRF protection mechanism against potential method overrides, SvelteKit 1.15.1 is now performing validation on PUT, PATCH and DELETE methods as well. This latter hardening is only needed to protect users who have put in some sort of ?_method= override feature themselves in their handle hook, so that the request that resolve sees could be PUT/PATCH/DELETE when the browser issues a POST request.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @sveltejs/kit | all versions | 1.15.1npm install @sveltejs/kit@1.15.1 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @sveltejs/kit, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update @sveltejs/kit to 1.15.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-29003 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2023-29003 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2023-29003. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2023-29003 in your dependencies?
O3 Security finds CVE-2023-29003 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.