Description

SvelteKit before 2.69.1 fails to properly validate remote form function payload sizes, allowing attackers to crash the Node process by sending large payloads. Repeated exploitation causes denial of service by repeatedly crashing the application process.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "5.3",
  "pubDate": "2026-08-28T12:16:38.457Z",
  "pubdate": "2026-08-28T12:16:38.457Z",
  "executiveSummary": "SvelteKit versions prior to 2.69.1 are susceptible to a Denial of Service (DoS) vulnerability originating from insufficient validation of remote form function payload sizes.\nThe vulnerability allows an unauthenticated remote attacker to trigger an application crash by submitting maliciously crafted, oversized form payloads.\nUpon receiving an excessively large payload, the underlying Node.js process fails to handle the memory or processing demand, leading to an immediate termination of the process.\nContinuous exploitation of this flaw can result in sustained service unavailability, impacting the overall availability of the affected web application.\nThe attack does not require prior authentication, making it a critical threat to public-facing SvelteKit instances.\nOrganizations using affected versions are at risk of resource exhaustion and service disruption, necessitating an urgent update to SvelteKit 2.69.1 or later.",
  "technicalDetails": "The vulnerability resides within the SvelteKit framework's mechanism for handling remote form function submissions. The root cause is identified as an improper validation logic applied to the size of incoming form payloads before they are processed by the framework's internal request handlers.\nIn a standard SvelteKit form action flow, the framework parses the request body to facilitate server-side state transitions. When a remote form function is invoked, the application expects structured data; however, the framework's implementation in versions before 2.69.1 fails to enforce strict size constraints on these serialized payloads.\nAn attacker can exploit this by crafting a POST request containing an abnormally large payload directed at a valid form action endpoint. Because the validation layer is deficient, the SvelteKit runtime allocates excessive resources—or enters an error state that it cannot gracefully recover from—when attempting to deserialize or parse the input stream.\nThe exploitation flow proceeds as follows: First, the attacker identifies an active form action endpoint exposed by the SvelteKit application. Second, the attacker transmits an HTTP request with a Content-Length header far exceeding expected business logic limits. Third, the Node.js server receives the oversized buffer; the SvelteKit framework attempts to process this payload, triggering an unhandled exception or critical memory pressure that forces the Node.js process to exit. Because Node.js is a single-threaded event-loop architecture for each process instance, the termination of the process renders the entire application instance unresponsive.\nThis vulnerability is particularly dangerous because the attack can be automated. An attacker can repeatedly send these oversized requests to ensure that every time the application process is restarted by a process manager (such as PM2 or systemd), it is immediately crashed again. This effectively creates a persistent, distributed, or single-source Denial of Service condition.\nThe impact is strictly limited to service availability; there is no evidence suggesting this vulnerability facilitates remote code execution or data exfiltration. However, by bypassing typical input size sanity checks, the attacker forces the framework into an unstable state, effectively circumventing the application's stability mechanisms and leading to total service disruption."
}