CVE-2026-22803 — @sveltejs/kit
Fix: sveltejs/kit@8ed8155CVE-2026-22803 is a CWE-789 vulnerability in @sveltejs/kit. A fix is available for @sveltejs/kit — see the affected versions and patch details below.
SvelteKit has a memory amplification DoS in Remote Functions binary form deserializer
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-22803.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
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 experimental form remote function uses a binary data format containing a representation of submitted form data. A specially-crafted payload can cause the server to allocate a large amount of memory, causing DoS via memory exhaustion.
Details
When a form is submitted to a remote function endpoint, the SvelteKit client encodes the data using a custom format, and POSTs it to the endpoint as a request with an application/x-sveltekit-formdata content type.
The first few bytes of the request body encode the length of the data. SvelteKit will attempt to read the request body up until the specified offset, but if the body is not yet available then an array buffer of that size will be created eagerly to accommodate it as it arrives.
An attacker can force this code path by sending a small payload that specifies a large data length, then stalling the connection. The resulting array buffer will be held in memory, potentially causing memory exhaustion.
Impact
- Vulnerability type: Availability / memory exhaustion (memory amplification).
- Who is impacted: SvelteKit apps with
experimental.remoteFunctionsenabled, and that expose a reachable Remote Form endpoint. - Attack: an unauthenticated attacker can repeatedly open connections, send only the 8-byte header/prefix (with large data_length), and stall the body to hold large allocations, exhausting memory.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @sveltejs/kit | ≥ 2.49.0&&< 2.49.5 | 2.49.5npm install @sveltejs/kit@2.49.5 |
Affected Products
kitsvelteDetection & 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 2.49.5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-22803 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
Frequently Asked Questions
Is CVE-2026-22803 in your dependencies?
Find it across npm, including transitive dependencies.