Details

Svelte was vulnerable to DOM clobbering of its internal framework state on elements, potentially leading to XSS attacks.

You are vulnerable if all of the following is true:

• you are using attribute spreading on a form element
• you are using attribute spreading or allow a dynamic value for the name attribute on an input or button element within that form
• both of these are simultaneously user-controllable

<form {...spread1}>
  <input {...spread2}>
</form>

Severity

• CVSS Score: Unknown
• Vector String: CVSS:4.0/AV:N/AC:H/AT:P/PR:L/UI:N/VC:L/VI:N/VA:N/SC:H/SI:H/SA:N

References

• https://github.com/sveltejs/svelte/security/advisories/GHSA-rcqx-6q8c-2c42
• https://github.com/sveltejs/svelte
• https://github.com/sveltejs/svelte/releases/tag/svelte%405.55.7

This data is provided by OSV and the GitHub Advisory Database (CC-BY 4.0).

Details

An internal regex in the Svelte runtime can take exponential time to test in <svelte:element this={tag}></svelte:element>. You are only vulnerable to this if you allow tags of unconstrained length. If your application only allows a predetermined list of tags or trims their length before passing them to svelte:element, you are safe.

Severity

• CVSS Score: Unknown
• Vector String: CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

References

• https://github.com/sveltejs/svelte/security/advisories/GHSA-9rmh-mm8f-r9h6
• https://github.com/sveltejs/svelte
• https://github.com/sveltejs/svelte/releases/tag/svelte%405.55.7

This data is provided by OSV and the GitHub Advisory Database (CC-BY 4.0).

Details

When using spread syntax to render attributes from untrusted data, event handler properties are included in the rendered HTML output. If an application spreads user-controlled or external data as element attributes, an attacker can inject malicious event handlers that execute in victims' browsers. Note that this vulnerability only triggers if the user's browser has JavaScript enabled but Svelte's hydration mechanism does not reach the vulnerable element before the event fires.

This is similar to but different from CVE-2026-27121.

Severity

• CVSS Score: Unknown
• Vector String: CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N

References

• https://github.com/sveltejs/svelte/security/advisories/GHSA-pr6f-5x2q-rwfp
• https://nvd.nist.gov/vuln/detail/CVE-2026-27121
• https://github.com/sveltejs/svelte
• https://github.com/sveltejs/svelte/releases/tag/svelte%405.55.7

This data is provided by OSV and the GitHub Advisory Database (CC-BY 4.0).

Details

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])

Severity

• CVSS Score: Unknown
• Vector String: CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N

References

• https://github.com/sveltejs/svelte/security/advisories/GHSA-f3cj-j4f6-wq85
• https://github.com/sveltejs/svelte/commit/a16ebc67bbcf8f708360195687e1b2719463e1a4
• https://github.com/sveltejs/svelte
• http://github.com/sveltejs/svelte/releases/tag/svelte%405.55.7

This data is provided by OSV and the GitHub Advisory Database (CC-BY 4.0).

v5.55.7

Compare Source

Patch Changes

• fix: prevent XSS on hydratable from user contents (a16ebc67bbcf8f708360195687e1b2719463e1a4)

• chore: bump devalue (#​18219)

• fix: disallow empty attribute names during SSR (547853e2406a2147ad7fb5ffeba95b01bd9642da)

• fix: harden regex (d2375e2ebcab5c88feb5652f1a9d621b8f06b259)

• fix: move Svelte runtime properties to symbols (e1cbbd96441e82c9eb8a23a2903c0d06d3cda991)

v5.55.6

Compare Source

Patch Changes

• fix: leave stale promises to wait for a later resolution, instead of rejecting (#​18180)

• fix: keep dependencies of $state.eager/pending (#​18218)

• fix: reapply context after transforming error during SSR (#​18099)

• fix: don't rebase just-created batches (#​18117)

• chore: allow null for pending in typings (#​18201)

• fix: flush eager effects in production (#​18107)

• fix: rethrow error of failed iterable after calling return() (#​18169)

• fix: account for proxified instance when updating bind:this (#​18147)

• fix: ensure scheduled batch is flushed if not obsolete (#​18131)

• fix: resolve stale deriveds with latest value (#​18167)

• chore: remove unnecessary increment_pending calls (#​18183)

• fix: correctly compile component member expressions for SSR (#​18192)

• fix: reset source.updated stack traces after flush (#​18196)

• fix: replacing async 'blocking' strategy with 'merging' (#​18205)

• fix: allow @debug tags to reference awaited variables (#​18138)

• fix: re-run fallback props if dependencies update (#​18146)

• fix: abort running obsolete async branches (#​18118)

• fix: ignore comments when reading CSS values (#​18153)

• fix: wrap Promise.all in save during SSR (#​18178)

• fix: ignore false-positive errors of $inspect dependencies (#​18106)

v5.55.5

Compare Source

Patch Changes

• fix: don't mark deriveds while an effect is updating (#​18124)

• fix: do not dispatch introstart event with animation of animate directive (#​18122)

v5.55.4

Compare Source

Patch Changes

• fix: never mark a child effect root as inert (#​18111)

• fix: reset context after waiting on blockers of @const expressions (#​18100)

• fix: keep flushing new eager effects (#​18102)

v5.55.3

Compare Source

Patch Changes

• fix: ensure proper HMR updates for dynamic components (#​18079)

• fix: correctly calculate @const blockers (#​18039)

• fix: freeze deriveds once their containing effects are destroyed (#​17921)

• fix: defer error boundary rendering in forks (#​18076)

• fix: avoid false positives for reactivity loss warning (#​18088)

v5.55.2

Compare Source

Patch Changes

• fix: invalidate @const tags based on visible references in legacy mode (#​18041)

• fix: handle parens in template expressions more robustly (#​18075)

• fix: disallow -- in idPrefix (#​18038)

• fix: correct types for ontoggle on <details> elements (#​18063)

• fix: don't override $destroy/set/on instance methods in dev mode (#​18034)

• fix: unskip branches of earlier batches after commit (#​18048)

• fix: never set derived.v inside fork (#​18037)

• fix: skip rebase logic in non-async mode (#​18040)

• fix: don't reset status of uninitialized deriveds (#​18054)

v5.55.1

Compare Source

Patch Changes

• fix: correctly handle bindings on the server (#​18009)

• fix: prevent hydration error on async {@​html ...} (#​17999)

• fix: cleanup superTypeParameters in ClassDeclarations/ClassExpression (#​18015)

• fix: improve duplicate module import error message (#​18016)

• fix: reschedule new effects in prior batches (#​18021)

v5.55.0

Compare Source

Minor Changes

• feat: export TweenOptions, SpringOptions, SpringUpdateOptions and Updater from svelte/motion (#​17967)

Patch Changes

• fix: ensure HMR wrapper forwards correct start/end nodes to active effect (#​17985)

v5.54.1

Compare Source

Patch Changes

• fix: hydration comments during hmr (#​17975)

• fix: null out effect.b in destroy_effect (#​17980)

• fix: group sync statements (#​17977)

• fix: defer batch resolution until earlier intersecting batches have committed (#​17162)

• fix: properly invoke iterator.return() during reactivity loss check (#​17966)

• fix: remove trailing semicolon from {@​const} tag printer (#​17962)

v5.54.0

Compare Source

Minor Changes

• feat: allow css, runes, customElement compiler options to be functions (#​17951)

Patch Changes

• fix: reinstate reactivity loss tracking (#​17801)

v5.53.13

Compare Source

Patch Changes

• fix: ensure $inspect after top level await doesn't break builds (#​17943)

• fix: resume inert effects when they come from offscreen (#​17942)

• fix: don't eagerly access not-yet-initialized functions in template (#​17938)

• fix: discard batches made obsolete by commit (#​17934)

• fix: ensure "is standalone child" is correctly reset (#​17944)

• fix: remove nodes in boundary when work is pending and HMR is active (#​17932)