MediumGHSA-f3cj-j4f6-wq85
Svelte: SSR XSS via Insecure Promise Serialization in hydratable
Published 14 May 2026 · Updated 14 May 2026
Affected package
sveltenpm
- Affected
- >=5.46.0 <5.55.7
- Fixed in
- 5.55.7
Update to the fixed version for your release line, for example:
npm install svelte@5.55.7Details
Contents of hydratable promises were not properly stringified, potentially leading to an XSS exploit. You are vulnerable if all of the following is true:
- you are using
hydratable(an experimental feature at the time of this report) - you are passing attacker-controlled input such that a synchronous value is hydrated, then a promise value, e.g.
hydratable('someKey', () => [synchronousValue, promiseValue])
Is GHSA-f3cj-j4f6-wq85 in any of your client repos?
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References
Advisory data from OSV.dev (opens OSV.dev in a new tab), refreshed daily.